Module 5 – Communication, Homeostasis & Energy

Question 1

C13) what is the definition of homoeostasis

Answer 1

The function of organs must be coordinated in order to maintain a relatively constant internal environment

Question 2

C13) what is cell signalling

Answer 2

Communication at a cellular level where one cell releases a chemical which has an affect on another cell called a target cell

Question 3

C13) What is the structure of a neurone

Answer 3

Cell body- contains the nucleus surrounded by cytoplasm. The cytoplasm contains large amounts of endoplasmic reticulum and mitochondria involved in the production of neurotransmitters, the chemicals used to pass signals from one Neurone onto the next

Dendrons- are short extensions which come from the cell body. Extensions divide into smaller and smaller branches known as dendrites responsible for transmitting electrical impulses towards cell body

Axons- singular, elongated nerve fibres that transmit impulses away from the cell body. These fibres can be very long, cylindrical in shape consisting of very narrow regions of cytoplasm

Question 4

C13) What is an myelinated neurones

Answer 4

The axons of some neurons are covered in a myelin sheath, made of many layers of plasma membrane.

Special cells called schwann cells produce the layers of membrane by Growing around the axon.

each time they grow around of the axon a double layer of phospholipid bilayer is laid down

When the cells stop growing there may be more than 20 layers of membrane

Between myelin sheath there is a gap called the node of ranvier

Question 5

C13) What is the importance of myelin sheath

Answer 5

Act as an insulating layer and allows these neurons to conduct the electrical impulses at a much faster speed

As the myelin sheath is an insulator the electrical impulse jumps from one node of ranvier to the next as it travels along the neuron allowing for faster transmission of current

In non-myelinated Neurons the impulse does not jump but transmits continuously along the neuron fibre so is much slower

Question 6

C13)What are the features of a sensory receptor

Answer 6

Specific to a single type of stimulus

They act as a transducer – convert a stimulus into a neuron impulse

Question 7

C13) How does a sensory receptor become a transducer

Answer 7

They detect a range of different stimulus. The receptor converts the stimulus into a nervous impulse called a generator potential

Question 8

C13) what is the purpose of cell signalling

Answer 8

Transfer signals locally. For example between neurons and synapses using neurotransmitters

Transfer signals across long distances using hormones. For example the pictureIt tree gland secretes ADH to act on the kidneys to maintain water balance

Question 9

C13) how does the pacinian corpuscle work

Answer 9

A specific sensory receptors that detect mechanical pressure located in your skin, fingers and the soles of your feet

The end of the sensory neuron is found within the centre of the corpuscle founded by connective tissue each layer of tissue is separated by layers of gel

The membrane of the neuron has sodium ion channels responsible for transporting sodium ions across the membrane but this sodium ion channel is special because it is stretch mediated

Question 10

C13) how does a pacinian corpuscle convert mechanical pressure into a nerve impulse

Answer 10

In its normal state the stretch mediated sodium ion channels in the sensory neurones membrane are too narrow to allow sodium ions to pass. It has a resting potential

When pressure is applied to the corpuscle it changes shape causing the membrane surrounding it’s neutrons to stretch

When the membrane stretches the sodium ion channels present widen allowing sodium ions to diffuse into the neuron

The influx of positive sodium ions changes the potential of the membrane it becomes depolarised resulting in a generator potential

The generator potential creates an action potential that passes along the sensory neuron. Action potential will be transmitted along neurons to the central nervous system

Question 11

C13) what is resting potential

Answer 11

When in your own is not transmitting and impose the potential difference across the membrane is known as a resting potential.

The outside of the membrane is more positively charged than the inside of the axon.

The membrane is said to be polarised as there is a potential difference across it

Normally about -70 mV

Question 12

C13) how is the resting potential created

Answer 12

Sodium ions (Na+) are actively transported out of the axon but the potassium ions (K+) are actively transported into the axon by a the sodium-potassium pump

For every 3 sodium ions pumped out, 2 potassium ions are pumped in therefore there are more sodium ions outside the membrane than inside the axon cytoplasm and also more potassium ions in the cytoplasm than outside the axon

So sodium ions diffused back into the axon down its electrochemical gradient whereas potassium ions diffused out of the axon but the gated sodium ion channels are closed preventing the movement of sodium ions but the potassium ion channels are open allowing potassium ions to defuse out of the axon as a result more positively charged ions are outside the axon than inside.

The inside is negative relative to the outside

Question 13

C13) What is depolarisation of the axon membrane

Answer 13

The energy of the stimulus temporarily reverses the charge on the axon membrane

The potential difference across the membrane rapidly changes and becomes positively charged at approximately 40mV.

A change in potential difference from negative to positive

Question 14

C13) What is the repolarisation of the axon membrane

Answer 14

After depolarisation, the membrane repolarisation occurs

A change in potential difference from positive back to negative returning to arresting potential

Question 15

C13) What is the sequence of events that takes place during an action potential

Answer 15

1) The nerve has a resting potential-not transmitting an impulse. Potassium ion channels are open but sodium voltage gated ion channels are closed
2) The stimulus triggers some sodium voltage gated ion channels to open making the membrane more permeable to sodium ions, diffusing into the axon down the electrochemical gradient making the inside of the neuron less negative
3) The change in charge causes more sodium ion channels to open allowing more sodium ions to diffuse into the axon-positive feedback
4) When the potential difference reaches 40mV the voltage gated sodium ion channels close and voltage gated potassium ion channels open. Sodium ions no longer into the axon but the membrane is now permeable to potassium ions
5) Potassium ions diffused out of the Exon down there electro chemical gradient reducing the charge resulting in the inside of the axon becoming more negative than the outside
6) Initially loads of potassium ions diffused out of the axon resulting in the inside of the axon becoming more negative than its normal resting potential- hyper polarisation. Voltage gated potassium channels close. The sodium potassium pump causes sodium ions to move out of the cell and potassium ions to move in the axon returns to its resting potential and is polarised

Question 16

C13) How is an action potential propagated along the axon to the end of a myelinated nerve

Answer 16

Initial stimulus causes an action potential in the sensory receptor.

So the first region of the axon membrane is depolarised acting as a stimulus for the depolarisation of the next region of the membrane through the use of localised electrical circuit

Process continues along the length of the axon forming a wave of depolarisation

Once sodium ions are inside the axon they are attracted by the negative change ahead and the concentration gradient to defuse further along inside the axon triggers the depolarisation of the next section

The region of the membrane which has been depolarised as the action potential passes along undergo Repolarisation to return to its resting potential

Question 17

C13) How does a propagation of action potential occur in a non-myelinated nerve

Answer 17

A stimulus causes a sudden influx of sodium ion and reverses the charge on the axon membrane causing an action potential and the membrane to depolarised

The localised Electrical circuit established by the influx of sodium ions cause the opening of sodium voltage gated channels a little further along the axon causing depolarisation. Behind the new region of depolarisation the sodium voltage gated channels close and potassium ones open. Potassium ions leave the axon along the electrochemical gradient

Continues along the length of the axon, Repolarisation occurs behind action potential

The axon as a result of repolarisation returns to normality

Question 18

C13) What is the refectory period of a neuron

Answer 18

After an Action potential there is a short time when the axon cannot be excited again

During this time The voltage gated sodium ion channels remain closed and prevent the movement of sodium ions into the axon

Question 19

C13) what is the importance of refractory period of a neuron

Answer 19

Because it prevents the propagation of an action potential backwards along the axon as well as forwards

Make sure action potentials are unidirectional

Insures that action potentials do not overlap and occur as a discrete impulse

Question 20

C13) how does saltatory conduction work

Answer 20

Myelinated axons transfer impulses faster than non-myelinated axons because depolarisation of the axon membrane can only happen at the node of Ranvier

this is the only place sodium ions can pass through the protein channels into the membrane

Larger localised circuits arise between adjacent roads allowing action potential then to jump from one load to another this called saltatory conduction

Question 21

C13) How does saltatory conduction increase the speed of an electrical impulse

Answer 21

Every time channels open and ions move it takes time so reducing the number of cases this happens speeds up the process

Long term it is more energy-efficient Repolarisation uses ATP in the sodium pump so reducing the amount of repolarisation needed makes the conduction of impulses more efficient

Question 22

C13) What factors affect the speed at which an action potential travels

Answer 22

Axon diameter – the bigger the axon diameter the faster the impulse transmits because there is less resistance to the flow of ions in the cytoplasm

Temperature-the higher the temperature the faster the nerve impulse because Ions always diffuse faster at high temperatures because up to about 40°C

Question 23

C13) what is the all or nothing principal of the transmission of an electrical impulse in a neuron

Answer 23

A certain level of stimulus (threshold value) always triggers a response.

If this threshold is reached an action potential is created no matter how large the stimulus is the same sized action potential is triggered. If the threshold is not reached there is no action potential

The size of the stimulus affects the number of action potential is generated in a given time. Large the stimulus the more frequent the action potentials are.

Question 24

C13) What are the structural components of a synapse

Answer 24

Synaptic cleft- the gap which separates the axon of one neuron from the dendrite of the next neurone

Presynaptic Neurone- Neurone along which the impulse has arrived

Postsynaptic Neurone- Neuron that receives the neurotransmitter

Synaptic knob- The end of the presynaptic Neuron containing mitochondria and endoplasmic reticulum to manufacture neurotransmitters

Synaptic vesicles- vehicles containing neurotransmitters. They fuse with the presynaptic membrane and release their contents into the synaptic cleft

Neurotransmitter receptors- receptor molecules which the neurotransmitter binds to in the postsynaptic membrane

Question 25

C13) What are the different types of neurotransmitters

Answer 25

Excitatory- neurotransmitters result in the depolarisation Of the postsynaptic nerve by triggering a action potential (acetylcholine) Inhibitory- neurotransmitters results in the hyperpolarisation of the postsynaptic membrane preventing an action potential to be triggered

Question 26

C13) How does a impulse transmit across the synapse

Answer 26

Action potential reaches the end of the presynaptic nerve Depolarisation of the presynaptic membrane causes calcium ion channels to open Calcium ions diffused into the presynaptic knob Causes synaptic vesiclesContaining neurotransmitters to fuse with the presynaptic membrane. Neurotransmitters are released into the synaptic class by exocytosis Neurotransmitters diffuse across the synaptic cleft and binds with the specific receptor molecules on the postsynaptic membrane Causing sodium ion channels to open allowing sodium ions to defuse into the postsynaptic neurone Triggering an action potential and the impulse is propagated along the postsynaptic neurone Neurotransmitters are removed by the stimulus not being maintained. So that other stimulus can arrive and affect the synapse Neurotransmitters left in the synaptic cleft is removed.

Question 27

C13) What happens to the neurotransmitter after an action potential is triggered in the postsynaptic neurone

Answer 27

Neurotransmitters are removed by the stimulus not being maintained. So that other stimulus can arrive and affect the synapse Neurotransmitters left in the synaptic cleft is removed. acetylcholine is broken down by enzymes, they also release them from the receptors of the postsynaptic membrane They are take back into the presynaptic knob The removal of neurotransmitters prevent the response from happening again and allows the neurotransmitters to be recycled

Question 28

C13) What is the cholinergic synapses and where can it be found

Answer 28

They use the neurotransmitter acetylcholine Common in the central nervous system of vertebra and at neuromuscular junction where a motoneuron and a muscle cell meet

Question 29

C13) what is the process of transmission across the cholinergic synapses

Answer 29

1) The arrival of the action potential at the end of the presynaptic nerve causes calcium ion channels to open and calcium ion enters the synaptic knob 2) The increase in calcium ions in the presynaptic neurone causes synaptic vehicles to fuse with the presynaptic membrane therefore releasing acetylcholine into the synaptic cleft 3) acetylcholine Molecules fuse with the receptor sites on the sodium ion channels in the membrane of the postsynaptic Neurone causing the sodium ion channels to open allowing sodium Ions to diffuse in along a concentration gradient 4) The sodium ions generate a new action potential in the postsynaptic nerve 5) acetylcholinesterase hydrolyse acetylcholine into choline and acetyl, They diffuse back into the presynaptic Neurone for recycling and to prevent generating a new action potential in the postsynaptic Neurone 6) ATP is used to re-combine choline and acetyl into acetylcholineStored in vesicles for future use. Sodium ion channels close because of the absence of acetylcholine

Question 30

C13) What is the role of the signups in the nervous system

Answer 30

Ensure impulses are unidirectional as neurotransmitter receptors are only present on the postsynaptic membrane impulses can only travel from the presynaptic nerve to the postsynaptic nerve Allow an impulse from one Neurone to be transmitted to a number of Neurons at multiple synapses resulting in a single stimulus creating in number of simultaneous responses A number of neurons may feed into the same synapse with a single postsynaptic Neurone resulting in a give stimuli from different receptors interacting to produce a single result

Question 31

C13) what is summation and control of a synapse

Answer 31

Stimulus from a presynaptic Neuron causes the release of some neurotransmitters Into the synapse. Some synapses however, the amount of neurotransmitters from a single impulse is not enough to trigger an action potential in the postsynaptic neurone because the threshold level isn’t reached Summation: If the amount of neurotransmitters build up significantly to reach the threshold then it will trigger an action potential

Question 32

C13) What is spatial summation of a synapse

Answer 32

Occurs when a number of presynaptic neurons connect to one postsynaptic neuron. Each releases neurotransmitters which build up to a high level to trigger an action potential

Question 33

C13) what is temporal summation of a synapse

Answer 33

Occurs when a single presynaptic nerve releases neurotransmitters as a result of an action potential several times in a short period. The buildup in the synapse reaches the threshold value and triggers the action potential in the postsynaptic neurone

Question 34

C13) what are the structural organisations of the nervous system of a mammal

Answer 34

Central nervous system- consists of the brain and the spinal cord peripheralNervous system- consists of all the Neurons that connects to the central nervous system to the rest of the body (sensory neurons, Motor neurons

Question 35

C13) What are the functional organisations of the nervous system in a mammal

Answer 35

Somatic nervous system- system is under conscious control. Used when you voluntarily decide to do something. (Contraction of muscles to move the arm) Autonomic nervous system- works constantly. Under subconscious control and is used when the body does something automatically without you deciding – involuntary (causes the heartbeat by carrying nerve impulses to the Cardiac muscle)

Question 36

C13) how is the Autonomic nervous system further organised functionally

Answer 36

Sympathetic nervous system- is if the outcome increases activity (increase heart rate) Parasympathetic nervous system- if the outcome decreases activity (a decrease in heart or breathing rate after exercise)

Question 37

C13) what is the gross structure of the Brain

Answer 37

Surrounded by a protective membrane called the meninges Cerebrum- controls voluntary activities such as learning, memory, personality and conscious thought Cerebellum- controls unconscious functions such as posture, balance and non-voluntary movement Medulla oblongata -used in autonomic control for example it controls heart rate and breathing rate Hypothalamus-regulatory control for temperature and water balance Pituitary gland-stores and releases hormones that regulate many body functions

Question 38

C13) what is the important information about the cerebrum

Answer 38

Receives sensory information and then sends impulses along motoneurons to affecters to produce a response Responsible for coordinating the body voluntary response Highly convoluted which increases its surface area considerably therefore increasing its capacity for complex activities The left and right halves are known as the cerebral hemisphere. Each hemisphere has specific functions devoted to specific areas The outer layer of the cerebral hemisphere is known as the cerebral cortex.

Question 39

C13) what is the importance of the frontal and pro frontal lobe of the cerebral cortex

Answer 39

Sophisticated processes such as reasoning and decision-making occur in the frontal and profrontal lobe of the cerebral cortex

Question 40

C13) what is the importance of sensory areas within the cerebral hemisphere

Answer 40

Sensory areas within cerebral hemispheres receive information from receptor cells in sensory organs. The size of the sensory area is proportional to the number of receptor cells present in that part of the body Then is passed onto the part of the brain known as the associated area to be analysed and acted upon Impulses then come to the motor area where motoneurons send out impulses The size of the motor area is proportional to the relative number of motor endings in it The main region that controls movement is the primary motor cortex located at the back of the frontal lobe

Question 41

C13) What happens at the base of the brain

Answer 41

Impulses from each side of the brain cross. The left hemisphere receives impulses from the right hand side of the body and the right hemisphere receives impulses from the left hand side of the body Impulses from the eye pass to the visual area in the occupational lobe. Impulses from the right side of the field of view in each eye are sent to the visual cortex in the left hemisphere and vice versa

Question 42

C13) what is the important information about the Cerebellum

Answer 42

Concerned with the control of muscular movement, body posture and balance – does not initiate movement but coordinates it If this part of the brain is damaged a person suffers from Jackie and uncoordinated movement Receives information from organs of balance in the ears and information about the tone of muscle and tendons Relate this information to the cerebral cortex, to the area of motor control

Question 43

C13) what is the important information about the Medela oblongata

Answer 43

Contains many important regulatory centres of the autonomic nervous system Controls reflex actions such as ventilation and heart rate Controls activities such as swallowing and coughing

Question 44

C13) what is the important information about the hypothalamus

Answer 44

Main controlling region for the autonomic nervous system Two controls- one for the parasympathetic and one for the sympathetic nervous system Functions include: Controlling complex patterns of behaviour such as feeding, sleeping and aggression Monitoring the composition of blood plasma such as the concentration of blood and blood glucose Producing hormones –it is an endocrine gland so it produces hormones such as antidiuretic hormone

Question 45

C13) what is the important information about the pituitary gland

Answer 45

Found at the base of the hypothalamus Control most of the glands in the body Divided into two sections: Anterior pituitary –produces six hormones including follicle-stimulating hormone which is involved in the reproduction and growth hormones Posterior pituitary- Stores and releases hormones produced by the hypothalamus, such as antidiuretic hormone

Question 46

C13) How does a knee-jerk reflects occur

Answer 46

A spinal reflex meaning that the natural circuit only goes up to the spinal-cord The latest tap just below the kneecap Stretches the patellar tendon and acts as a stimulus. Stimulus initiates a reflex arc that causes the extensor muscle on top of the thigh to contract At the same time a relay neurone inhibits the motor neuron of the flexor muscle causing it to relax The contraction coordinated with the relaxation of the antagonistic flexor hamstring Causing the leg to kick The absence of the reflex may indicate nervous problems and Multiple Sclerosis of the legs

Question 47

C13) why does a blinking reflects occur

Answer 47

Because of the cornea is stimulated to prevent it from being damaged due to foreign bodies this type of response is known as a corneal reflex Blink reflex also occurs when sounds great than 40 to 60 dB are heard or as a result of very bright light to protect the lens and retinal is known as an optical reflex A blinking reflex is a cranial reflex, occurs in the brain

Question 48

C13) how does a blinking reflex occur

Answer 48

When the cornea is irritated by foreign bodies, The stimulus triggers an impulse along a sensory Neuron The impulse then passes through a relay neuron in the lower brainstem Impulses are then sent along branches of the motor neuron to initiate a motor response to close the eyelids The reflex initiates a consensual response- means that both eyes are closed in response to the stimulus Doctors test for blinking reflexes when examining unconscious patients. If the reflexes present it indicates the lower brainstem is functioning. Used to determine whether patient is brain-dead

Question 49

C13) why are reflexes considered important for survival

Answer 49

Reflexes avoid the body from being harmed or reduce the severity of any damages. For example the iris constricts the pupil to prevent light from damaging the retina Bringing involuntary responses- the decision-making region of the brain is not involved therefore the brain is able to deal with more complex responses preventing the brain being overloaded Not have to Learned- they are present at birth and therefore provide immediate protection Extremely fast- the reflex arc is very short normally involves one or two synapses Many reflexes are considered to be everyday actions such as the control of digestion

Question 50

C13) What are the types of muscle

Answer 50

Skeletal muscle - makes up the bulk of body muscle tissue. The cells responsible for movement for example the biceps and triceps Cardiac muscle - are found only in the heart. Are myogenic meaning they contract without the need for a nervous stimulus causing the heart to beat in a regular rhythm Involuntary muscle (smooth-muscle)- found in many parts of the body for example the walls of hollow organs such as the stomach and bladder

Question 51

C13) what are the differences between skeletal, cardiac and involuntary muscle

Answer 51

The appearance of fibre in skeletal muscle is striated while cardiac muscle have specialised striated tissue and within involuntary muscle it is non-striated Control of skeletal muscle is conscious and voluntary while cardiac muscle and involuntary muscles are in voluntarily controlled Arrangement of fibres in skeletal muscle is regular so that muscles can contract in One Direction. They arrangement of the fibres in the cardiac muscle is branched and interconnected resulting in simultaneous contraction. In voluntary muscles have no regular arrangement different cells can contract in different directions The structure of skeletal muscle is striated and fibre are tubular and multinucleated. The cardiac muscle does have striations but are more fainter than skeletal muscle and Fibres are branched and uninuclated. In voluntary muscles have no cross-section striations and fibres are spindle shaped and uninuclated

Question 52

C13) what is the structure of a muscle fibre

Answer 52

Skeletal muscle is made up of bundles of muscle fibres Muscle fibres are enclosed within a plasma membrane known as the sarcolemma Muscle fibres contain nuclei which are longer than normal cells formed because of individual embryonic muscle cells fusing together allowing the muscle to be stronger as the junctions between adjacent cells are a point of weakness The shared cytoplasm within a muscle fibre is called sarcoplasm Parts of the sarcolemmal are folded inwards known as transverse to help spread electrical impulses throughout the sarcoplasm Allows the whole fibre to receive the impulse to contract at the same time Muscle fibre have loads of mitochondria to provide the ATP needed for muscle contraction they have a modified version of endoplasmic reticulum known as the sarcoplasmic reticulum. Contains calcium ions require for muscle contraction and is throughout the whole muscle fibre

Question 53

C13) what is the structure of myofibrils

Answer 53

Every muscle fibre contains many myofibrils They are long cylindrical organelles made of proteins and specialised for contraction. On the phone they provide almost no force but collectively they are very powerful. Myofibrils all lined up in parallel to provide maximum force when they contract together

Question 54

C13) what type of proteins make up myofibrils

Answer 54

Actin- the thinner filament. Consists of two strands twisted around each other Myosin- the thicker filament. Consist of long rod shaped fibres with bulbous heads that project to one side

Question 55

C13) what is the light band of a myofibril

Answer 55

Area appears light as they are the region where the acting and myosin filaments do not overlap Known as isotopic bands or I bands

Question 56

C13) what is the dark bands band of a myofibril

Answer 56

Area appear darker because of the presence of thick myosin filaments Edges are particularly dark as the myosin is overlapped with acting Anisotropic Band or A band

Question 57

C13) what is the z-line of a myofibril

Answer 57

Line found at the centre of each light band The distance between adjacent deadlines is called a sarcomere The sarcoma is the functional unit of myofibril. When a muscle contracts the sarcomere shortens

Question 58

C13) what is the H-zone of a myofibril

Answer 58

Lighter coloured regions found in the centre of each dark band Only myosin filaments are present at this point When the muscle contracts the H-Zone decreases

Question 59

C13) what is the sliding filament model

Answer 59

The acting and myosin filaments within the myofibril has to slide past each other Therefore muscle contraction is usually described as this

Question 60

C13) what is the result of the myosin filament pulling the actin filament inwards towards the centre of the sarcomere cause

Answer 60

The light band becomes narrow The sideline moves closer together shortening the sarcomere The H zone becomes narrower The dark band remains the same width as the myosin filaments themselves are not shortened but overlap the actin filament by a greater amount The simultaneous contraction of loads of sarcomeres mean that the myofibril and muscle fibres contract. Therefore there is enough force to pull on a bone and cause movement When is sarcomere returned to their original length the muscle relaxers

Question 61

C13) What is the structure of myosin

Answer 61

Filaments have globular heads that are hinged which allow them to move back and forwards The head is a binding site for actin and ATP Tales of several hundred myosin molecules are aligned together to form a myosin filament

Question 62

C13) What is the structure of actin

Answer 62

Actin filament have a binding site for myosin heads called actin-myosin binding site The binding sites are often blocked by the presence of other proteins called tropomyosin which are held in place by the protein troponin

Question 63

C13) What happens to actin and myosin when the muscle is that rest

Answer 63

When muscle is at rest the actin-myosin sites are blocked by tropomyosin. The myosin heads cannot bind to the actin so the filament cannot slide past each other

Question 64

C13) what happens to acting and myosin when the muscle is contracted

Answer 64

When the muscle is contracted The myosin heads form bonds with acting filaments known as actin-myosin cross bridges. The myosin head changes angle in union pulling the actin filament along the myosin filaments. Myosin and then detaches from the actin and its heads return to its original angle using ATP. The myosin reattach is further along the actin filament and the process occurs again

Question 65

C13) how does the neuromuscular junction cause a muscle contraction to occur

Answer 65

Triggered when an action potential arrives at a neuromuscular junction (point where a motor neurone and a skeletal muscle fibre meet) Many neuromuscular junction is along the length of the muscle to ensure all muscle fibres contract simultaneously. If a strong force is needed a large number of Motor units are stimulated whereas only a small number are stimulated if a small force is required When an action potential reaches the neuromuscular junction. It stimulates calcium ion channels to open, calcium ions diffused into the synaptic knob where they cause synaptic vesicles to fuse with the presynaptic membrane Acetylcholine is released into the synaptic cleft by exocytosis and defuses across the synapse binding to receptors on the sarcolemma. Opening sodium ion channels and resulting in depolarisation

Question 66

C13) what happens if only one neuromuscular junction was available

Answer 66

If only one existed the muscle fibre would not contract together therefore the contraction of the muscle would not be powerful. Also be much slower as a wave of contraction would have to travel along the muscle to stimulate the individual fibres to contract

Question 67

C13) what is a motor unit

Answer 67

All the muscle fibres supplied by a single neuron are known as motor unit - the fibres act as a single unit

Question 68

C13) what happens to Acetylcholine after an action potential passes neuromuscular junction

Answer 68

It is broken down by Acetylcholinesterase into choline and ethanolic acid This prevents the muscle being overstimulated Choline and ethanolic acid diffuse back into the neuron where they are re-combined into Acetylcholine using energy provided by mitochondria

Question 69

C13) what happens to the sarcolemma when the electrical current passes the intramuscular junction

Answer 69

depolarisation of the sarcolemma travels deep into the muscle by spreading through the t-tubules which are in contact with the sarcoplasmic reticulum containing stored calcium ions which is actively absorbed by the sarcoplasm As the action potential gets to the sarcoplasmic reticulum stimulating the calcium ions channels to open. Calcium ion diffuse dawn their concentration gradient into the sarcoplasm The calcium ions bind to troponin causing it to change shape. This pulls on the tropomyosin moving it away from the actin-myosin binding site on the actin filament. The myosin head binds to the actin filament forming a actin-myosin Crossbridge

Question 70

C13) what happens after the myosin heads attach to the actin filament

Answer 70

The head flex, pulling the actin filament along. The molecule of ADP bound to the myosin head is released. An ATP molecule can now bind the myosin head causing the head to detach from the actin filament The calcium ions present in the sarcoplasm activate ATPase activity of the myosin. Hydrolysing the ATP to ADP and phosphate releasing energy which the myosin heads used to return to its original position The myosin heads can now attach itself to another actin-myosin binding site further along the actin filament and the cycle is repeated while the muscle remains stimulated. During a period of stimulation many acts in myosin bridges form and break pulling the actin filament along, shortening the sacrament and causing the muscle to contract

Question 71

C13) how and why is energy used during muscle contraction

Answer 71

Provides energy for muscle contraction is by the hydrolysis of ATP into ADP and phosphate The energy is required for the movement of the myosin heads and to enable the sarcoplasmic reticulum To actively re-absorb calcium ions from the Sarcoplasm

Question 72

C13) What are the different ways energy is supplied for muscle contraction

Answer 72

Aerobic respiration- most of the ATP used is generated from ATP during oxidative phosphorylation. The reaction happens in the mitochondria which are plentiful in muscles. Only occur in the presence of oxygen. is used for long periods of low intensity exercise Anaerobic respiration- in very active muscles oxygen is used more quickly than the blood supply can replace it. ATP is therefore generated anaerobically. ATP is made by glycolysis but as no oxygen is present, The pyruvate which is produced is converted into lactic acid which can quickly buildup in the muscles resulting in fatigue. Is used for short periods of high intensity exercise Creation phosphate- Body can generate ATP by using the chemical creation phosphate which is stored in the muscles. To form ATP, ADP has to be phosphorylated which creation phosphate acts as a reserve supply off. phosphate which is available immediately. This system generates ATP rapidly, but the store of phosphate is used up quickly. This is used for short bursts of vigourous exercise. when the muscle is relaxed the creation phosphate is replenished using phosphate from ATP

Question 73

C17) What is the importance of ATP production in photosynthesis

Answer 73

It provides the energy needed to build organic molecules like glucose Energy is used to form chemical bonds in ATP which are then broken to relieve the energy needed to make bonds as glucose is formed

Question 74

C17) What is the importance of ATP production in respiration

Answer 74

Organic molecules such as glucose or broken down and the energy released is used to synthesise ATP ATP is then used to supply the energy needed to break Bonds in the metabolic reactions of cells

Question 75

C17) What is chemiosmosis

Answer 75

Process by which ATP is produced in both photosynthesis and respiration Involves the diffusion of protons from a region of high concentration to a region of low concentration through a semipermeable membrane Movement of the protons as they flow down the concentration gradient releases energy that is used in the attachment of an inorganic phosphate to ADP forming ATP Depends on the creation of a proton concentration gradient.The energy to do this comes from high energy electrons

Question 76

C17) what are the ways in which electrons are raised to higher energy levels

Answer 76

Electrons present in pigment molecules are excited by absorbing light from the Sun High energy electrons are released when chemical bonds are broken in respiratory substrate molecules Excited electrons pass through a electron transfer chain and are used to generate a proton (H+) gradient

Question 77

C17) What are the stages of chemiosmosis with the use of an electron transport chain

Answer 77

An electron transport chain is made up of a series of electron carriers with progressively lower energy levels. As higher energy electrons move from one Carrier to another, energy is released which is used to pump protons Across a membrane creating a concentration difference and a proton gradient. The proton gradient is maintained because of the permeability of the membrane to hydrogen ions Protons can move down the concentration gradient through hydrophilic membrane channels linked to the enzyme ATP synthase. The flow of protons through these channels provide the energy used to synthesise ATP from ADP and phosphate ions

Question 78

C17 what are the structures and functions of chloroplast

Answer 78

The network of membranes present within the chloroplast provides a large surface area to maximise the absorption of light essential for photosynthesis Membranes form flattened sacs called thylakoids which are stacked to form grana which are joined by membrane channels called lamella Light is absorbed by complex pigments such as chlorophyll embedded within the thylakoids membrane The fluid include in the chloroplast is called the stroma and is the site of many chemical reaction resulting in the formation of complex organic molecules

Question 79

C17) what is the function of chlorophyll in photosynthesis

Answer 79

Pigment molecules Absorb specific wavelengths of light and reflect others. Different pigments absorb and reflect on different wavelengths that is why they have different colours Primary pigment is chlorophyll in photosynthesis, mainly absorbs red and blue light and reflects Green light. Large quantities of chlorophyll is the reason for the green colour implants A number of different pigments that absorb light, The primary pigment is chlorophyll A and other pigments like chlorophyll b,xanthophyll absorb different wavelengths of light than those absorbed by chlorophyll A. Combinations of pigments are the reason for different shades and colours of leaves

Question 80

C17) how is a photosystem constructed

Answer 80

chlorophyll b and xanthophyll are embedded in the thylakoids membrane of the Chloroplast, these and other proteins and pigments form a light harvesting system (Antennae complex) which has the role to absorb or harvest light energy in different wavelength and transfer this energy quickly and efficiently to the reaction centre Chlorophyll a is located in the reaction centre which is where the reactions involved in photosynthesis take place The light harvesting system and the reaction centre is collectively known as a focus system

Question 81

C17) what happens to the protons that are released during photolysis

Answer 81

The protons (H+) is released into the Lumen of the thylakoids increasing the proton concentration across the membrane. They moved back through the membrane down a electrochemical gradient driving the formation of more ATP. Once the hydrogen ions are returned to the stroma they are combined with NADP with an electron from photosystem one to form reduced NADP. Used by the light independent reaction of photosynthesis. This process removes hydrogen ions from the stroma so it helps to maintain the proton gradient across the thylakoids membranes

Question 82

C17)What happens during non-cyclic phosphorylation of photosynthesis

Answer 82

2 photosystems are involved with non-cyclic phosphorylation. The reaction centre of photosystem 2 absorbs wavelength of 680nm while photosystem 1 absorbs higher wavelengths of 700nm The light absorbed excites electrons and the reaction centre of the photo system The excited electrons are released from the reaction centre of PS2 and are passed to an electron transport chain. ATP is produced by the process of Chemiosmosis. The electrons lost from the reaction centre of PS2 are replaced from water molecules are broken down using energy from the Sun Excited electrons are released from the reaction centre of PS1 passing another Electron transport chain, and ATP is produced again by Chemiosmosis. The electrons lost from the reaction centre are replaced by electrons travelling from PS2 The electrons leaving the electron transport chain from PS1 are excepted with hydrogen ions by the coenzyme NADP forming a reduced NADP

Question 83

C17) what is the importance of reduced NADP

Answer 83

Provides the hydrogen or reducing power in the production of organic molecules such as glucose in the light independent stage

Question 84

C17) what occurs during photolysis

Answer 84

Oxygen evolving complex which forms part of PS2 is an enzyme that catalyse is the breakdown of water Water molecules are split into hydrogen ions, electrons and oxygen molecules using energy from the Sun The electrons replace the electrons lost from the reaction centre of PS2 Oxygen gas is released as a by product The protons are released into the lumen of the thylakoids increasing the proton concentration across the membrane. As they move back through the membrane down a concentration and electrochemical gradient to drive the formation of more ATP Once the hydrogen ions are released to the stroma they combine with NADP and an electron to form a reduced NADP This process removes hydrogen ions from the stromuhr to help maintain the proton gradient across the thylakoids membrane

Question 85

C17) what is the equation for photolysis

Answer 85

H2O = 2H+ + 2e- + 0.5O2

Question 86

C17) how does cyclic phosphorylation occur

Answer 86

The electrons leaving the electron transport chain off the PS1 can be returned to PS1 instead of being used to form reduce NADP PS1 can still lead to the production of ATP without any electrons being supplied from PS2 Reduced NADP is not produced when this happens

Question 87

C17) what is the light independent stage of photosynthesis

Answer 87

Takes place in the stroma of chloroplasts Uses carbon dioxide as a raw material The products of the light dependent stage - ATP and reduced NADPAre required Organic molecules are produced in reactions within the Calvin cycle

Question 88

C17) what are the stages of the Calvin cycle

Answer 88

Carbon dioxide enters the intercellular spaces within the spongy Mesophyll of leaves by diffusion from the atmosphere into the stomata. Defuses into the stroma of chloroplasts where it combines with a five carbon molecule called Ribulose bisphosphate. The carbon in carbon dioxide is therefore fixed into an organic molecule The enzyme Ribulose bisphosphate carboxylase catalyses the reaction and an unstable six carbon intermediate is produced. The unstable six carbon compound breaks down forming 2 3 carbon glycerate3 phosphate molecules Each GP molecule is converted to another three carbon molecule, triose phosphate using a hydrogen atom from reduced NADP and energy supplied by ATP From the light Dependent reaction TP is a carbohydrate, a three carbon sugar TP molecules are recycled to regenerate Ribulose bisphosphate so the Calvin cycle can continue and is the starting point for complex biological molecules

Question 89

C17) How important is ruBisCO to photosynthesis

Answer 89

RuBisCO is a key enzyme in photosynthesis, a very ineffective enzyme as it is completely inhibited by oxygen so a lot of it is needed to carry out photosynthesis successfully.

Question 90

C17) what are the three summarise steps to the Calvin cycle

Answer 90

Fixation - carbon dioxide is fixed in the first step Reduction - GP is reduced to TP by the addition of hydrogen from reduced NADP using energy supplied by ATP Regeneration - Ribulose bisphosphate is re-generated from recycled TP

Question 91

C17) How does the regeneration of Ribulose bisphosphate occur

Answer 91

For one glucose molecule to be produced six carbon dioxide molecules have to enter the Calvin cycle Resulting in the production of 12 TP molecules, two of which will be removed to make glucose molecules Meaning that 10 TP molecules are recycled to generate six Ribulose bisphosphate molecules 10 * 3-Carbon TP = 30 carbons/ 5 carbon Ribulose bisphosphate = 6 Energy is supplied by ATP for the reaction involved in regenerating Ribulose bisphosphate

Question 92

C17) what are the three limiting factors of photosynthesis

Answer 92

Light intensity Carbon dioxide concentration Temperature - affects the rate of enzyme controlled reactions.

Question 93

c17) how does the stomata affect photosynthesis

Answer 93

Will close to avoid water loss by transpiration during dry spells The closure of the stomata stops the diffusion of carbon dioxide into the plant reducing the rate of the light independent reaction and stopping photosynthesis

Question 94

C17) why is water not considered to be a limiting factor in photosynthesis

Answer 94

Because for water potential to have become low enough to limit the rate of photosynthesis the plant will have closed it’s stomata and ceased photosynthesis and therefore unlikely to survive

Question 95

C18) what is cellular respiration

Answer 95

The carbon framework of glucose is broken down and the carbon hydrogen bonds broken The energy released is then used in the synthesis of ATP by Chemiosmosis Prokaryotic cells have a similar process but they do not have mitochondria so many of the reactions take place on the cell membrane

Question 96

C18) What is glycolysis

Answer 96

Occurs in the cytoplasm of the cell Does not require oxygen – it is an aerobic process Glucose, six carbon sugar is split into two smaller, three carbon pyruvate molecules ATP and reduced NAD are also produced

Question 97

C18) what are the main steps in glycolysis

Answer 97

Phosphorylation - requires two molecules of ATP. Two phosphate released from the two ATP molecules are attached to a glucose molecule forming hexose bisphosphate Lysis - this destabilises the molecule causing it to split into two triose phosphate molecules Phosphorylation - another phosphate group is added to each triose phosphate forming to triose bisphosphonate. The phosphate groups come from free inorganic phosphate ions present in the cytoplasm Dehydrogenation and formation of ATP - the 2 triose bisphosphate molecules are then oxidised by the removal of hydrogen atoms (Dehydrogenation) to form two pyruvate molecules. NAD coenzymes except the removed hydrogens - they are reduced forming reduced NAD molecules. 4 ATP molecules are produced using phosphates from the triose bisphosphonate molecule

Question 98

C18) what is substrate level phosphorylation

Answer 98

The formation of ATP without the involvement of an electron transport chain. ATP is formed by the transfer of a phosphate group from a phosphorylated intermediate to ATP

Question 99

C18) what is the net yield of ATP in glycolysis

Answer 99

Two molecules of ATP from glycolysis As to ATP molecules are used to prime the process at the beginning and for ATP molecules are produced

Question 100

C18) how is the mitochondria structured for aerobic respiration

Answer 100

Crusta our projections of the inner membrane which increases the surface area available for oxidative phosphorylation Inner mitochondrial membrane contains electron transport chain and ATP synthase Matrix contains enzymes for the Krebs cycle and the link reaction also contains mitochondrial DNA In a membrane space, proteins are pumped into the space by the electron transport chain. The space is small so the concentration builds up quickly

Question 101

C18) what is oxidative decarboxylation

Answer 101

First step in aerobic respiration Sometimes referred to as the link reaction because it is the step that links anaerobic glycolysis occurring in the cytoplasm to the aerobic steps of respiration occurring in the mitochondria

Question 102

C18) what are the steps of oxidative decarboxylation

Answer 102

In eukaryotes pyruvate enters the mitochondrial matrix by active transport via specific carrier proteins Pyruvate undergoes oxidative decarboxylation Carbon dioxide is removed (decarboxylation) along with hydrogen (oxidation) The hydrogen atom is removed or excepted by NAD. NAD is reduced to form NADH or reduced NAD Resulting in a 2 carbon acetyl group which is bound by coenzyme a forming acetylcoenzyme A Acetyl group is known as ethanoyl group

Question 103

C18) What happens to the products of oxidative decarboxylation

Answer 103

acetylcoenzyme A delivers the acetyl group to the next stage of aerobic respiration known as the Krebs cycle The reduced NAD is used in oxidative phosphorylation to synthesise ATP The carbon dioxide produced to either diffuse away and be removed as metabolic waste or in autotrophic organisms may be used as raw material in photosynthesis

Question 104

C18) What is the krebs cycle

Answer 104

Takes place in the mitochondrial matrix Each complete cycle breaks down and acetylgroup Involves decarboxylation, dehydrogenation and substrate level phosphorylation The hydrogen atoms released of picked up by the coenzyme NAD and FAD Carbon dioxide is a byproduct of the reaction ATP produced is available for use by energy requiring processes Reduced NAD and reduced FAD produced are used in oxidative phosphorylation to produce large quantities of ATP by Chemiosmosis

Question 105

C18) What are the stages of the Krebs cycle

Answer 105

acetylcoenzyme A delivers an acetyl group to the kerbs cycle. The two carbon acetyl group combines with four carbon oxaloacetate to form six carbon citrate The citrate molecule undergoes decarboxylation and dehydrogenation producing one reduced NAD and carbon dioxide. A five carbon compound is formed The five carbon compound undergoes further decarboxylation and dehydrogenation eventually regenerating oxaloacetate and the cycle continues. Producing carbon dioxide, 2 reduced NAD, One reduced FAD and ATP is also produced by substrate level phosphorylation

Question 106

C18) what is the importance of coenzymes in respiration

Answer 106

Coenzymes are required to transfer protons, electrons and functional groups between many of enzyme catalysed reactions Redox reactions have an important role in respiration and without coenzymes transferring electrons and protons between these reactions many respiratory enzymes would not function NAD and FAD are both coenzymes that accept protonsAnd electrons releasing during breakdown of glucose in respiration

Question 107

C18) what is the difference between NAD and FAD

Answer 107

NAD takes part in all stages of cellular respiration but FAD the only except hydrogens in the Krebs cycle NAD except one hydrogen and FAD except two hydrogens Reduced NAD is oxidated at the start of the electron transport chain releasing protons and electrons while reduced FAD is oxidised further along the chain Reduced NAD results in the synthesis of three ATP molecules but reduced FED results in the synthesis of only two ATP molecules

Question 108

C19) how does oxidative phosphorylation occur

Answer 108

The hydrogen atoms collected by coenzymes NAD and FAD are delivered to the electron transport chain present in the membrane of the Cristae Hydrogen atoms dissociate into hydrogen ions and electrons.The high energy electrons are used to synthesise ATP by chemiosmosis Energy is released during redox reactions as the electrons reduce and oxidised electron carriers as they flow along the electron transport chain. The energy is used to create a proton gradient leading to the diffusion of protons along ATP synthase resulting in ATP synthesis At the end of the electron transport chain electrons combined with hydrogen ions and oxygen to form water.Oxygen is the final electron exceptor and the electron chain cannot operate without oxygen

Question 109

C18) what is oxidative phosphorylation

Answer 109

The phosphorylation of ADP to form ATP is dependent on electrons moving along electron transport chain. This requires the presence of oxygen Oxidative phosphorylation

Question 110

C18)What is fermentation

Answer 110

Process by which complex organic compounds are broken down into similar inorganic compounds without the use of oxygen or the involvement of an electron transport chain Organic compounds such as glucose are not fully broken down so fermentation processes less ATP than aerobic respiration Small quantities of ATP produced is synthesised by substrate level phosphorylation

Question 111

C18) what is alcohol fermentation

Answer 111

Different type of fermentation for different organisms Occurs in yeast and some plant root cells The end products are ethanol and carbon dioxide

Question 112

C18)What is lactate Fermentation

Answer 112

A different type of fermentation Lactate fermentation results in the production of lactate and is carried out in animal cells

Question 113

C18) why does fermentation occur

Answer 113

There is no oxygen to act as a final electron Exceptor at the end of the electron transport chain in oxidative phosphorylation, the flow of electrons stop meaning the synthesis of ATP by Chemiosmosis stops As the flow ofElectrons has stopped, the reduced NAD and FAD are no longer able to be oxygenated because there is nowhere for the electrons to go Means FAD and NAD cannot be regenerated and so the decarboxylation and oxidisation of pyruvate and the Krebs cycle comes to a halt as there are no coenzymes available to except the hydrogen being removed The process of fermentation allows NAD for glycolysis

Question 114

C14Why is the pituitary gland in close proximity to the hypothalamus

Answer 114

To ensure the nervous and hormonal responses of the body are closely linked and coordinated

Question 115

C14)What is the importance of the pituitary gland

Answer 115

Produces growth hormones which control growth of bones and muscles Antidiuretic hormone which controls reabsorption of water in kidneys Genodotropin Which control development of the ovaries and testes

Question 116

C14) what is the pineal gland

Answer 116

Produces melatonin which affects reproductive development and daily cycles

Question 117

C14) what is the importance of the thyroid gland

Answer 117

Produces thyroxine which controls rate of metabolism and rate that glucose is used up in respiration and promotes growth

Question 118

C14) what is the importance of the thymus gland

Answer 118

Produces thymosin which promotes production and maturation of white blood cells

Question 119

C14) what is the importance of the adrenal glands

Answer 119

Produces adrenaline which increases heart rate and breathing rate and raises blood sugar levels

Question 120

C14) what is the importance of the pancreas gland

Answer 120

Produces insulin which converts excess glucose into glycogen in the liver Glucagon which converts glycogen back into glucose in the liver

Question 121

C14) what is the importance of the testes

Answer 121

Produces testosterone which controls sperm production and secondary sexual characteristics

Question 122

C14) what is the importance of the ovaries

Answer 122

Produces oestrogen which controls ovulation and secondary sexual characteristics And progesterone which prepares the uterus lining to receive an embryo

Question 123

C14) what is the difference between endocrine glands and exocrine glands

Answer 123

Exocrine glands secrete chemicals through ducts into organs or to the surface of the body Endocrine glands secrete chemicals directly into the blood

Question 124

C14) what are hormones

Answer 124

Referred to as chemical messengers because they carry information from one part of the body to another Can be steroids, proteins, glycoproteins, Polypeptide Hormones are secreted directly into the blood when a gland is stimulated which can occur because of a change in concentration of a particular substance, as a result of another hormone or a nerve impulse

Question 125

C14) how does hormone action occur

Answer 125

Once secreted, hormones are transported in the blood plasma. The hormones diffuse out of the plasma and binds to specific receptors for that hormone, found on the membrane or in the cytoplasm of the cell in the target organ, Known as target cells Once bound to the receptor the hormones emulate the target cells to produce a response

Question 126

C14) how does a steroid hormone affect a target cell

Answer 126

Are lipid soluble Passed through the lipid compound of the cell membrane and bind to steroid hormone receptors to form a hormone receptor complex The receptors may be present in the cytoplasm or the nucleus depending on the hormone The hormone receptor complex formed acts as a transcription factor which in turn facilitate or inhibit the transcription of a specific gene

Question 127

C14) how does non-steroid hormones affect a target cell

Answer 127

Are hydrophilic so cannot pass directly through the cell membrane Instead and bind to specific receptors on the cell surface membrane of the target cell Triggers a cascade reaction mediated by chemicals called secondary messengers

Question 128

C14) what are the important parts of the hormonal system

Answer 128

Communication is by chemicals called hormones Transmission is by the bloodstream Transmission is usually relatively slow Hormones travel to all parts of the body but only target organs respond Response is widespread Response is slow Response is often long-lasting Effects may be permanent and irreversible

Question 129

C14) what is the important parts of the nervous system

Answer 129

Communication is by nerve impulses Transmission is by neurons Transmission is very rapid Nerve impulses travel to specific parts of the body Response is localised Responses rapid Response is short lived Effect is temporary and reversible

Question 130

C14 what are the important parts of the adrenal glands

Answer 130

Located on top of the kidneys and made up of two distinct parts surrounded by a capsule The adrenal cortex-the outer region of the gland, produces hormones that are vital to life such as Cortisol The adrenal medulla-the inner region of the gland, produces non-essential hormones such as adrenaline which helps the body to react to stress

Question 131

C14) How is the adrenal cortex stimulated and What are the main types of hormones produced by the adrenal cortex

Answer 131

Production of hormones by the adrenal cortex is it self controlled by hormones released from the pituitary gland in the brain Three main types of hormones: Glucocorticoids Mineralocorticoids Androgens

Question 132

C14) what are examples and roles of Glucocorticoids

Answer 132

Glucocorticoids - Cortisol helps regulate metabolism by controlling how the body converts fats, proteins and carbohydrates to energy. Helps regulate blood pressure and cardiovascular functions in response to stress. Release of these hormones is controlled by the hypothalamus

Question 133

C14) what are examples and roles of Mineralocorticoids

Answer 133

Aldosterone which helps to control blood pressure by maintaining the balance between salt and water concentration in the blood and body fluid Its release is mediated by signals triggered by the kidney

Question 134

C14) what are examples and roles of Androgens

Answer 134

Small amount of male and female sex hormones are released, impact is relatively small compared with the large amount of hormones but they are still important especially in women after the menopause

Question 135

C14) how is the adrenal Modella stimulated and what Are the Hormones they secrete

Answer 135

Sympathetic Nervous system is stimulated the hormones of the adrenal medulla is released Adrenaline- increases the heart rate sending blood quickly to the muscles and brain.Also rapidly rises blood glucose concentration levels by converting glycogen into glucose in the liver Noradrenaline- works with adrenaline in response to stress producing effects such as increased heart rate, widening of the pupils, widening of the air passages in the lungs and narrowing of blood vessels in non-essential organs resulting in higher blood pressure

Question 136

C14) What are the two main functions of the pancreas

Answer 136

Exocrine gland - produces enzymes and releases them via A duct into the duodenum Endocrine gland- produces hormones and releases them into the blood

Question 137

C14) what is the role of the pancreas as an exocrine gland

Answer 137

Made up of exocrine glandular tissue is responsible for producing digestive enzymes and an alkaline fluid known as pancreatic juice Secreted into ducts which eventually lead to the pancreatic duct, released into the duodenum, top part of the small intestine. Produces three types of digestive enzyme: Amylase -Break down starch into simple sugars Protease-breaks down proteins into amino acids Leipus-breaks down lipids into fatty acids and glycerol

Question 138

C14) What is the role of the pancreas as an endocrine gland

Answer 138

Responsible for producing insulin and glucagon Essential role in controlling blood glucose concentration Within the exocrine tissue there are small regions of endocrine tissue called islets of Langerhans. The cells of the islets of Langerhans are responsible for producing insulin and glucagon and secretes hormones into the bloodstream

Question 139

C14) what does the different parts of the pancreas look like under the microscope

Answer 139

Endocrine tissue-islets of Langerhans, lightly stained large spiracle clusters-produces and secretes hormones Exocrine tissue-pancreatic acini, darker stained, small Berry like clusters-produce and secrete digestive enzymes

Question 140

C14) what are the islets of Langerhans classified into

Answer 140

Within the islets of Langerhans there are different types of cells, classified according to the hormone they secrete Alpha cells-produce and secrete glucagon Beta cells-produce and secrete insulin Alpha cells are larger and more numerous than beta cells within an islet of Langerhans

Question 141

C14) What are the reasons for blood glucose concentration to increase

Answer 141

Diet- when you eat carbohydrate rich foods such as pasta and rice and sweet foods such as cake and fruit,The carbohydrate is broken down in the digestive system to release glucose. The glucose released is absorbed into the bloodstream. Gluconeogenesis – the production of glucose from non-carbohydrate sources. The liver is able to make glucose from glycerol and amino acid. The glucose released is absorbed into the bloodstream. Glycogenolysis -glycogen stored in the liver and muscle cells is broken down into glucose. The glucose released is absorbed into the bloodstream.

Question 142

C14) how can blood glucose concentrations be decreased

Answer 142

Respiration- some of the glucose in the blood is used by cells to release energy, required for normal body functions. During exercise more glucose is used as the body needs to generate more energy in order for muscle cells to contract, The higher the physical activity,the higher the demand for glucose,the greater the decrease of blood glucose concentration Glycogenesis-production of glycogen, Blood glucose concentration is too high excessive glucose is converted into glycogen which are stored in the liver

Question 143

C14) what is the role of insulin

Answer 143

Insulin is produced by beta cells of the islets of Langerhans in the pancreas If blood glucose concentration is too high the beta cells detect this raise and respond by secreting insulin directly into the bloodstream All body cells have insulin receptors on the cell surface membrane . Insulin binds to its glycoprotein receptor, causing a change in the tertiary structure of the glucose transport protein channel, causing the channel to open allowing more glucose to enter the cell Also activates enzymes within some cells to convert glucose to glycogen and fat Insulin is broken down by enzymes in the cells of the liver. Therefore maintaining the effect means continuously secreting the hormone As blood glucose concentrations return to normal this is detected by the beta cells of the pancreas if it falls below a certain level, the beta cells reduces the secretion of the insulin-negative feedback

Question 144

C14) how does insulin lower blood glucose concentration

Answer 144

Increasing the rate of absorption of glucose by cells in particular skeletal muscle cells Increasing the respiratory rate of cells-this increases the need for glucose and causes a higher uptake of glucose from the blood Increasing the rate of glycogenesis-insulin stimulates the liver to remove glucose from the blood by turning glucose into glycogen and storing it in the liver and muscle cells Increasing the rate of glucose to fat conversion Inhibiting the release of glucagon from the alpha cells of the islets of Langerhans

Question 145

C14) what is the role of glucagon

Answer 145

Glucagon is produced by the alpha cells of the islets of Langerhans in the pancreas If blood glucose concentration is too low the alpha cells detect the fall in blood glucose concentration and respond by secreting glucagon into the bloodstream The only cells in the body which have glucagon receptors are the liver cells and fat cells-these are the only cells that can respond to glucagon As blood glucose concentration returns to normal, Is detected by the alpha cells of the pancreas when it rises above a certain level that alpha cells reduce the secretion of glucagon-negative feedback

Question 146

C14) how does glucagon increase blood glucose concentration

Answer 146

Glycogenolysis-liver breaks down its glycogen stored into glucose and releases it back into the bloodstream Reducing the amount of glucose absorbed by the liver cells Increasing gluconeogenesis-increasing the conversion of amino acids and glycerol into glucose in the liver

Question 147

C14) what are the interactions of insulin and glucagon

Answer 147

Insulin and glucagon are antagonistic hormones-they work against each other The system of maintaining blood glucose concentration is said to be self regulating as it is the level of glucose in the blood that determines the quantity of insulin and glucose that is released Blood glucose concentration is not constant but fluctuates around a set point as a result of negative feedback

Question 148

C14) How is insulin released by the beta cells of the islets of Langerhans

Answer 148

At normal blood glucose levels, potassium channels in the plasma membrane of the beta cells are open and potassium ions diffuse out of the cell. The inside of the cell is that a potential of -70 mV compared to the outside When blood glucose concentration raises, glucose enters the cell by a glucose transporter The glucose is metabolised inside the mitochondria resulting in the production of ATP The ATP binds to potassium channels and causes them to close. Known as ATP sensitive potassium channels As potassium ions cannot longer diffuse out of the cell the potential difference reduces to around -30 millivolts and depolarisation occurs Depolarisation causes voltage gated calcium channels to open Calcium ions into the cell and cause secretary vesicles to release the insulin they contain by exocytosis

Question 149

C14) what is diabetes

Answer 149

Your pancreas either does not produce enough insulin or your body cannot effectively respond to the insulin produced

Question 150

C14)What is type one diabetes

Answer 150

Are unable to produce insulin The beta cells of the islets of Langerhans do not produce insulin Cause is not known and so at the moment the disease cannot be prevented or cured but can treat the symptoms Condition arises as a result of an autoimmune response where the bodies own immune system attacks the beta cells Begins in childhood and people develop symptoms of the disease quickly

Question 151

C14) what is type two diabetes

Answer 151

Cannot effectively use insulin and control blood sugar levels Either because the persons beta cells do not produce enough insulin or the persons body cells do not respond properly to insulin Often because the glycoprotein insulin receptors on the cell membrane does not work properly, The cells lose their responsiveness to insulin and therefore do not take up enough glucose, leaving it in the bloodstream Largely as a result of excess body weight, physical activity and habitual excessive overeating of carbohydrates Less of it and develop slowly in comparison to type one diabetes Only diagnosed after complications have Arisen Risk of type two diabetes increase with age

Question 152

C14) what are the treatments for type one diabetes

Answer 152

Type one diabetes is controlled by regular injection of insulin and is therefore said to be insulin-dependent People with the condition have to regularly test their blood glucose concentration, normally by pricking my fingers. The drop of blood is analysed by a machine which tells the person about glucose concentration. Based on the concentration the person can work out the doses of insulin they need to inject Insulin administered increases the amount of glucose absorbed by cells and cause glycogenesis to occur resulting in the reduction of blood glucose concentration Too much insulin can result in hypoglycaemia and too little insulin can result in hyperglycaemia

Question 153

C14) what are the treatments for type two diabetes

Answer 153

To regulate the persons carbohydrate intake through the diet and matching this to the exercise level Often involves increasing exercise levels Overweight people often encouraged to lose weight Drugs also have to be used that stimulate insulin production, drugs that slow down the rate at which the body absorbs glucose from the intestine

Question 154

C14) what are the advantages of using genetically modified bacteria to produce insulin

Answer 154

Human insulin is produced in a pure form-means it is less likely to cause allergic reactions Insulin can be produced in much higher quantities Production costs are much cheaper Peoples concerns of using animal products in humans which may be religious or ethical are overcome

Question 155

C14) what are the different treatment for diabetes

Answer 155

Pancreatic transplant Injecting patients with pancreas beta islets of Langerhans cells Stem cells

Question 156

C14) what were the problems associated with injecting patients with pancreatic beta islet cells

Answer 156

Fewer than 8% of cell transplant performed have been successful No suppressant drugs used to prevent rejection of the cells increase metabolic demand on insulin producing cells This exhaust their capacity to produce insulin

Question 157

C14) how can stem cells be used to treat type one diabetes

Answer 157

Toti potent stem cells have the potential to grow into any type of the bodies cell Scientists are researching the best type of stem cell and the signals required to promote their differentiation into beta cells Likely that the stem cells used in diabetes treatments would be taken from embryos, early embryo has to be destroyed meaning a potential human life has to be destroyed. Embryos used as sources of stem cells would usually be destroyed-they are spare embryos from infertility treatment or from terminate pregnancies Alternative to using embryonic stem cells is to use umbilical stem cells

Question 158

C14) What are the advantages of using embryonic stem cells to treat type one diabetes in comparison to current therapies

Answer 158

Doughnut availability would not be an issue-stem cells can produce an unlimited source of new beta cells Reduce likelihood of rejection problems as embryonic stem cells are generally not rejected by the body. Stem cells can also be made by stomatic cells nuclear transfer People no longer have to inject themselves with insulin

Question 159

C14) what are the disadvantages of using stem cells to treat diabetes

Answer 159

Our ability to control growth and differentiation in stem cells is still limited Concerns in whether any precursor or stem like cells transplanted into the body might induce the formation of tumours as a result of unlimited cell growth

Question 160

C14) what is the fight or flight response

Answer 160

An instinct that all mammals possess When a potential dangerous situation is detected the body automatically triggers a series of physical responses These help mammals survive by preparing the body to either run or fight for life

Question 161

C14) what happens when a threat is detected.

Answer 161

Is detected by the autonomy nervous system, the hypothalamus communicates with the sympathetic nervous system and the adrenal Cortical system. The sympathetic nervous system uses neural pathways to initiate body reactions Adrenal Cortical System uses hormones in the bloodstream. The combined effects of the 2 systems results in the fight or flight response The sympathetic nervous system sends out impulses to glands and smooth muscle and tells the adrenal medulla to release adrenaline and Noradrenaline -distress hormones caused several changes in the body

Question 162

C14) how does other stress hormones other than adrenaline and noradrenaline

Answer 162

Hormones with a long-term action from the adrenal cortex is controlled by the hormones produced by the pituitary gland in the brain The hypothalamus stimulates the pituitary gland to secrete adrenocorticotropic hormone. This travels in the bloodstream to the adrenal cortex where it activates the release of many hormones that prepare the body to deal with a threat

Question 163

C14) what are the physical responses of flight or fight and what are their purpose

Answer 163

Heart rate increases - to pump more oxygenated blood around the body Pupils dilate - to take in as much light as possible for better version Arterioles in skin constrict - more blood to major groups, brain, heart and muscles of ventilation blood glucose level increases -more respiration to provide energy for muscle contraction Smooth-muscle of airways relax-to allow more oxygen into the lungs

Question 164

C14) what is one of the main functions of adrenaline

Answer 164

During the fight or flight response it triggers the liver cells to undergo glycogenolysis so that glucose is released into the bloodstream to allow for respiration to increase in turn allowing more energy for muscle contraction Adrenaline is a hormone that is hydrophilic therefore cannot pass through the cell membrane Adrenaline binds with receptors on the surface of the liver cell membrane and triggers a chain reaction inside the cell

Question 165

C14) what is the reaction chain caused inside the cell by adrenaline

Answer 165

The hormone adrenaline approaches receptor site Adrenaline fuses to receptor site, and in doing so activates an enzyme inside the membrane called adenylyl cyclase adenylyl cyclase triggers the conversion of ATP into cyclic adenosine mono-phosphate on the inner surface of the cell membrane in the cytoplasm The increase in cAMP levels activate specific enzymes called protein Kinases which phosphorylates, and enhance activate, other enzymes which in turn trigger the conversion of glycogen into glucose

Question 166

C14) what is the secondary messenger model

Answer 166

This model of human action has the hormone as the first messenger and cAMP as the second messenger One hormone molecule can cause many cAMP molecules to be formed At each stage the number of molecules involved increases so the process is said to have a cascade effect

Question 167

C14) how is heart rate controlled

Answer 167

Harriet is involuntary and controlled by the autonomous nervous system The medulla oblongata in the brain is responsible for controlling heart rate and making any necessary changes Two centres within the medulla oblongata linked to the Sino atrial node in the heart by motoneurons

Question 168

C14) what are the two centres of the medulla oblongata that control heart rate

Answer 168

One centre increases heart rate by sending impulses through the synaptic nervous system these impulses are transmitted by the Excelerator nerve The second sentence decreases heart rate by sending impulses through the parasympathetic nervous system, these impulses are transmitted by the Vegas nerve

Question 169

C14)How does the medulla oblongata know which centre to stimulate

Answer 169

Depends on information received by receptors in the blood vessels There are two types of receptors which provide information That affect the heart

Question 170

C14) what are the two types of receptors which provide information that affect heart rate

Answer 170

Baroreceptor-these receptors detect changes in blood pressure, if a persons blood pressure is low the heart rate needs to be increased to prevent fainting Barrow receptors are present in the aorta, vena cava and The carotid artery Chemoreceptors- these receptors detect changes in the level of particular chemicals in the blood such as carbon dioxide. Chemo receptors are located in the aorta, The carotid arteryAnd the medulla

Question 171

C14) what is the importance of chemoreceptors when carbon dioxide levels increase

Answer 171

Chemo receptors are sensitive to changes in pH level of the blood If carbon dioxide levels in the blood increases the pH of the blood decreases because in Carbonic acid is formed when carbon dioxide interact with water in the blood The chemo receptor detects a decrease in blood pH, a response is triggered to increase heart rate therefore more blood flows more quickly to the lungs for gases exchange.

Question 172

C14) what is the importance of chemoreceptors when carbon dioxide levels decreases back to normal

Answer 172

When carbon dioxide levels decrease, the pH of the blood rises which is detected by the chemo receptors in the walls. Result in a reduction in the frequency of the nerve impulse being sent to the medulla oblongata This reduces the frequency of the impulses being sent to the Sino atrial node through the sympathetic nervous system Therefore Heart rate decreases back to its normal levels

Question 173

C14) what is the importance of baroreceptors when blood pressure is too high

Answer 173

Barrow receptors detect changes in pressure Impulses are sent to the medulla oblongata Centre which decreases heart rate The medulla oblongata sends impulses along parasympathetic nerves to the Sino atrial node which decreases the rate at which the heartbeat Reduces blood pressure back to normal

Question 174

C14) what is the importance of baroreceptors when blood pressure is too low

Answer 174

Impulses are sent to the medulla oblongata centre which increases heart rate The medulla oblongata sends impulses along sympathetic nerves to the Sino atrial node which increases the rate at which the heartbeats Increases blood pressure back to normal

Question 175

C14) how does hormonal console affect heart rate

Answer 175

Heart is also influenced by the presence of hormones Adrenaline and nuraadrenaline hormones affect the pacemaker region of the heart itself-they speed up your heart rate by increasing the frequency of impulses produced to the Sino atrial node

Question 176

C15) what is the meaning of homeostasis

Answer 176

The body maintains a dynamic equilibrium, with small fluctuations over in a narrow range of conditions

Question 177

C15) what are receptors

Answer 177

Sensory receptors detect change in the internal and external environment of an organism In homeostasis it is essential to monitor changes in the internal environment The pH of the blood, core body temperature and the concentration of urea

Question 178

C15) what are effectors

Answer 178

Information from the sensory receptor is transmitted to the brain and impulses are sent along the motor neuron to the affected to bring about changes to restore the equilibrium in the body All the muscles or glands that react to the motor stimulus to bring about a change in response to a stimulus

Question 179

C15) what is a negative feedback system

Answer 179

Most of the feedback systems in the body involves negative feedback A small change in One Direction is detected by sensory receptors. As a result effectors work to reverse the change and restore conditions to the base level Negative feedback systems work to reverse the initial stimulus

Question 180

C15) what is a positive feedback system

Answer 180

Relatively few positive feedback systems in the body In a positive feedback system, a change in the internal environment of the body is detected by sensory receptors and effectors are stimulated to reinforce the change and increase the response.

Question 181

C15) what is the meaning of Thermoregulation

Answer 181

The maintenance of a relatively constant core body temperature to maintain optimum enzyme activity

Question 182

C15) What are the physical processes that result in organisms heating up and cooling down

Answer 182

Exothermic chemical reaction Latent heat of evaporation – an object cools dawn as water evaporates from the surface Convection - the heating and cooling by currents of air or water, warm air or water rises and cooler air or water sinks setting up convection currents around an organism Conduction-heating as a result of the collision of molecules. Air is not a good conductor of heat but the ground or water are.

Question 183

C15) what are ectotherm

Answer 183

Most animals are ectotherms Use their surroundings to warm their bodies Their core body temperature is heavily dependent on the environment Include all the invertebrate animals, fish amphibians and reptiles Many ectotherm is living in water do not need to thermo regulate. The high heat capacity of water means that the temperature of the environment does not change much Ectotherm that live on land had a bigger problem with temperature regulation as temperature of the air can vary dramatically between seasons and even 24 hour period

Question 184

C15) what are endotherms

Answer 184

Mammals and birds are endotherms Rely on the metabolic processes to warm up and they usually maintain a very stable core body temperature regardless of the temperature of the environment Have adaptations which enable them to maintain their body temperature and to take advantage of warmth from the environment Keeping warm in cold conditions and cooling down in hot conditions are both active processes The metabolic rate of endotherms higher than ectotherms so they need to consume more food to meet their metabolic need.

Question 185

C15) How do ectotherm regulate temperature

Answer 185

Ectotherm is cannot control their body temperature using their metabolism They have evolved a range of behavioural responses that enable them to overcome the limitations imposed by the temperature of their surrounding

Question 186

C15) what are the behavioural responses adapted by ectotherms to increase body temperature

Answer 186

Behaviours which increased or reduced the radiation they absorb from the Sun. Sometimes they need to warm up, to reach a temperature, where their metabolic reactions happen fast enough for them to be active. They may bask in the Sun, orientate their bodies so that the maximum surface area is exposed to the Sun and even extend areas of the body to increase the surface area exposed to the Sun Ectotherms can increase their body temperature through conduction by placing their bodies against the warm ground. They also get warmer as a result of exothermic metabolic reactions

Question 187

C15) what are the behavioural responses adapted by ectotherms to decrease body temperature

Answer 187

Ectotherms sometimes need to cool down to prevent their enzymes denaturing as a result of high core body temperature. Many of the warming processes are reversed, seeking shelter, hiding in cracks in rocks or even digging borrows. Press the body against cool, shady stones or move into available water or mud They orientate their bodies so that the minimum surface area is exposed to the Sun and minimise their movement to reduce the metabolic heat generated

Question 188

C15) what are the psychological responses to warming that ectotherms have

Answer 188

Dark colours absorb more radiation than light colours Some ectotherms also alter the heart rate to increase or decrease the metabolic rate and sometimes to affect the warming or cooling across the body surface

Question 189

C15) how are temperature changes detected in endotherms

Answer 189

The peripheral temperature receptors in the skin detect change in the surface temperature Temperature receptors in the hypothalamus detect the temperature of the blood deep in the body. The temperature of the skin is much more likely to be affected by external conditions than the temperature of the hypothalamus

Question 190

C15) what is the importance of having the two temperature receptors for Thermoregulation of endotherm’s

Answer 190

The combination of the two gives the body great sensitivity and allows it to respond not only to actual changes in the temperature of the blood but to pre-empt possible problems that might result from changes in external temperature The temperature receptors in the hypothalamus Acts as the thermostat for the body controlling the response that maintains the core temperature in a dynamic equilibrium.

Question 191

C15) what are the principles associated with thermoregulation in endotherms

Answer 191

Endotherm’s use internal exothermic metabolic activity to keep them warm and energy requiring physiological responses to keep them Cool They have passive ways of heating up and cooling down to reduce the energy demand on their bodies Have a range of behavioural responses to temperature changes that include basking in the Sun pressing themselves to warm surfaces wallowing in the water and mud to cool down and digging borrows to keep warm or cool Endotherm’s rely on physiological adaptations to maintain stable core body temperature regardless of the environmental conditions or the amount of exercise being done

Question 192

C15)What on the common responses to Decrease body core temperature in endotherm’s

Answer 192

Vasodilation Increased sweating Reducing the insulin effect of hair or feathers

Question 193

C15) how does vasodilation Decrease body core temperature in endotherm’s

Answer 193

The arteries near the surface of the skin dilate when the temperature rises The vessels that provide a direct connection between the arterioles and the venules constrict forcing blood through the capillary networks close to the surface of the skin The skin flushes and cools as a result of increased radiation, if the skin is pressed against cool surfaces then the cooling results from condensation

Question 194

C15) how does increased sweating Decrease body core temperature in endotherm’s

Answer 194

As the core temperature starts to increase, rate or sweating also increases Sweat spreads out across the surface of the skin As a sweat evaporates on the surface of the skin heat is lost cooling the body below the surface In some animals sweat glands are restricted to less hairy areas of the bodies. These animals often open their mouth and paint when they are hot again losing heat as the water evaporates Some often lick their front legs to keep cool in high temperature

Question 195

C15) how does reducing the insulating effects of hair or feather Decrease body core temperature in endotherm’s

Answer 195

As the body temperature begins to increase, the erector pili muscles in the skin relax, therefore the hair or feather of the animal Lie flat on the skin,this Avoids trapping any insulating layer of air has little effect in humans Endotherm’s that live in hot climates often have anatomical adaptations as well as behavioural and physiological. These minimise the effects of high temperature and maximise the ability of the animal to cool down through the surface area of the body. Include a relatively large surface area to volume ratio to maximise cooling and the shedding of fur

Question 196

C15)What on the common responses to increase body core temperature in endotherm’s

Answer 196

Vasoconstriction Decrease sweating Rising the body hair or feather Shivering

Question 197

C15) how does vasoconstriction increase core body temperature in endotherm’s

Answer 197

The office is near the surface of the skin is constricted The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin The skin looks pale and very little radiation takes place The warm blood is kept well below the surface

Question 198

C15) how does decreased sweating increase core body temperature in endotherm’s

Answer 198

As the core temperature falls, Right of sweating decreases and sweat production will stop eventually Greatly reduces cooling down by the evaporation of water from the surface of the skin although some evaporation from the lungs still continue

Question 199

C15) how does raising the body hair or feathers increase core body temperature in endotherm’s

Answer 199

As body temperature falls, the erector Pili muscle in the skin contract pulling the hair or further of the animal erect Traps and insulating layer of air and so reduces cooling through the skin Can be quite dramatic and it is a very effective way to reduce heat loss to the environment in many animals

Question 200

C15) how does shivering increase core body temperature in endotherm’s

Answer 200

As the body temperature falls the body may begin to shiver The rapid, in voluntary contracting and relaxing of large voluntary muscles in the body The metabolic heat from the exothermic reaction to warm up the body instead of moving it and is an effective way of raising the core temperature

Question 201

C15)How does endotherm’s who live in cold climates adapt to thermoregulation

Answer 201

many have adaptations that minimise the surface area to volume ratio to reduce cooling Another common adaptation is a thick layer of insulating fat underneath the skin Some animals hibernate-they build up fat stores, build a well insulated shelter and lower their metabolic rate so they passed the worst of the cold weather in a deep sleep like state

Question 202

C15) How is Thermoregulation controlled in endotherms

Answer 202

The physiological responses Of endotherm is to changes in the core temperature are the result of complex homeostatic mechanisms involving negative feedback control from the hypothalamus

Question 203

C15) what are the two centres involved in controlling thermoregulation in endotherms

Answer 203

The heat loss centre - activated when the temperature of the blood flowing through the hypothalamus increases. Sends impulses through autonomic motor neurons to effectors in the skin and muscles triggering responses to lower the core temperature The heat gain centre - activated when the temperature of the blood flowing through the hypothalamus decreases. Sends impulses through autonomic motor neurons to effectors in the skin and muscles triggering responses to lower the core temperature

Question 204

C15)What is the meaning of excretion

Answer 204

The removal of waste products of metabolism from the body

Question 205

C15) what are the main metabolic waste products excreted in mammals

Answer 205

Carbon dioxide - one of the waste products for cellular respiration which is excreted from the lungs Bile pigments - formed from the breakdown of haemoglobin from old red blood cells in the liver. Secreted in the bile from the liver into the small intestine via the gallbladder and bile duct. Colour the faeces Nitrogenous waste products - formed from the breakdown of excess amino acids by the liver. All animals produce urea as their nitrogenous waste. Fish produce ammonia while birds and insects produce uric acid

Question 206

C15) What is the General information about the liver

Answer 206

Lies just below the diaphragm and is made up of several lobes. is very fast growing and damaged areas generally did regenerate very quickly The liver has a very rich blood supply-oxygenated blood supply to the liver by the hepatic artery and removed from the liver and returned to the heart in the hepatic vein. The liver is also supplied with blood by a second vessel the hepatic portal vein The hepatic portal vein carries blood loaded with the products of digestion straight from the intestines to the liver and this is the starting point for many metabolic activities of the liver

Question 207

C15) what is the structure of the liver

Answer 207

Liver cells or hepatocyte have large nuclei, permanent Golgi apparatus and lots of mitochondria indicating they are metabolically active cells. They divide and replicate-even if 65% of the liver is lost it will regenerate in a matter of months Blood from the hepatic artery and the hepatic portal vein is mixed in spaces called sinusoids which are surrounded by hepatocytes. This mixing increases the oxygen content of the blood from the hepatic portal vein supplying the hepatocytes with enough oxygen for their needs The sinusoids contain kupffer cells which act as the resident microphage of the liver digesting foreign particles and helping to protect against disease The hepatocyte secrete bile from the breakdown of the blood into spaces called canaliculi and from these the bile drains into The bile ducts which take it to the gallbladder

Question 208

C15) what are the three functions of the liver

Answer 208

Carbohydrate metabolism Deamination of excess amino acids Detoxification

Question 209

C15) How does the liver metabolise carbohydrates

Answer 209

Hepatocytes are closely involved in the homeostatic control of glucose levels in the blood by their interactions with insulin and glucagon Insulin levels rise and stimulate hepatocytes to convert glucose to the storage carbohydrate glycogen When blood sugar levels start to fall the hepatocyte convert the glycogen back to glucose because of the hormone glucagon

Question 210

C15) how does the liver deaminate excess amino acids

Answer 210

Vital role in protein metabolism where hepatocytes synthesise most of the plasma proteins Also carry out transamination - The conversion of one amino acid into another, important because the diet does not always contain the required balance of amino acids therefore transamination can overcome this problem Deamination - The removal of an amine group from a molecule. As the body cannot Store either proteins and amino acids, any excess ingested proteins would be secreted and therefore wasted if not for the hepatocytes. They deaminate The amino acid and converting it first into ammonia which is very toxic and then to urea, which is toxic in high concentrations but not in concentrations normally found in the body. Urea is excreted in the kidneys The remainder of the amino acids can be fed into cellular respiration or converted into lipids for storage

Question 211

C15) what is the ornithine cycle

Answer 211

Ammonia produced in the deamination of proteins is converted into urea in a set of enzyme Removing a amino group from amino acids and converting the highly toxic ammonia to less toxic and more manageable compound urea involves complex biochemistry

Question 212

C15) what are the stages of the ornithine cycle

Answer 212

Deamination of excess amino acid = ammonia (Ammonia + ornithine + carbon dioxide) - water = Citruline (Citruline + ammonia) - water = arginine (arginine + water)- releases urea = ornithine

Question 213

C15) how does the liver detoxify toxins

Answer 213

The levels of toxins in the body always tend to increase Metabolic pathways produce potentially poisonous substances and we also take variety of toxins by choice such as alcohol and drugs. The liver is the site when most of the substances or detoxified and made harmless Deliver detoxifies the ethanol in alcoholic drinks. Hepatocytes contain the enzyme alcohol dehydrogenase that break down ethanol into ethanal,Ethanal is converted to ethanoate, used to build up the fatty acids or used as a respiratory substrate

Question 214

C15)What are the two important homeostatic roles of the kidneys

Answer 214

Involved in excretion Osmoregulation They filter nitrogenous waste products out of the blood especially urea Help maintain the water balance and pH of the blood

Question 215

C15) what is the anatomy of the kidney

Answer 215

The kidneys are supplied with blood at arterial pressure by the renal arteries that branch off from the abdominal aorta Blood that has circulated through the kidneys is removed by the renal vein that drains into the inferior vina Carver Made up of millions of small structures called nephrons that act as filtering units The sterile liquid produced by the kidney tubules is called urine The urine passes down out of the kidneys through tubes called ureters Collected in the bladder When the bladder is getting for the splinters at the end of the bladder opens and the urine passes out of the body down the urethra

Question 216

C15) what is the structure of the kidney

Answer 216

The cortex - the dark outer layer, where the filtering of the blood takes place and it has a very dense capillary network carrying the blood from the renal artery to the nephrons The Medulla - Lighter in colour, contains the tubules of the nephron that formed the pyramid of the kidney and the collecting duct The pelvis - the centre chamber where the urine collect before passing down the ureter

Question 217

C15 what is the importance of the nephron

Answer 217

In the nephrons the blood is filtered and the majority of the filtered material is returned to the blood, removing nitrogenous waste and balancing the mineral ions and water 1.5 million nephrons in each kidney, provide the body with several kilometres of tubules for the reabsorption of water, glucose, salt and other substance back into the blood

Question 218

C15) what are the structures of the nephron

Answer 218

The Bowmans capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct Has a network of capillaries around it which finally lead into a vein then to the renal vein. The blood that leaves the kidney has generally reduced levels of urea but the levels of glucose and other substances needed by the body are almost the same as when the blood enters the kidney

Question 219

C15)What is the Bowmans capsule of a nephron

Answer 219

Cup shaped structure that contains the glamorulus, A tangle of capillaries. More blood goes into the glamorulus then it leaves because of ultrafiltration

Question 220

C15)What is the proximal convoluted tubule of a nephron

Answer 220

First, coiled region of the tubule after the Bowmans capsule Found in the cortex of the kidneys Where many of the substances needed by the body are reabsorbed into the blood

Question 221

C15)What is the loop of Henle of a nephron

Answer 221

A long loop of tubule that creates a region with a very high solute concentration in the tissue fluid in the kidney Medulla Descending loop runs down from the cortex through the medulla to a hairpin bend at the bottom of the loop. The ascending limb travels back through the medulla to the cortex

Question 222

C15) What is the distal convoluted tubule of a nephron

Answer 222

A second twisted tubule where the fine-tuning of the water balance of the body takes place The permeability of the walls to water varies in response to the levels of the anti-diuretic hormone in the blood Further regulation of the iron balance and pH of the blood also takes place in this tubule

Question 223

C15) What is the collecting duct of a nephron

Answer 223

The urine passes down the collecting duct through the middle to the pelvis More fine-tuning of the water balance takes place, walls of this part of the tubules are also sensitive to antidiuretic hormone

Question 224

C15) what are the two functions of the nephron

Answer 224

Ultrafiltration Reabsorption

Question 225

C15) How does the nephrons ultrafiltrate

Answer 225

Specialist form of the process that results in the formation of tissue fluid in the capillary beds of the body as a result of the structures of the glomerulus and the cells lining the Bowmans capsule The glomerulusIs supplied with blood by a relatively wide afferent arteriole from the renal artery, blood leaves through a narrow efferent arteriole, therefore higher pressure in the capillaries of the glomerulus Forces the blood out through the capillaries, like a sieve, the fluid passes through the basement membrane (very important in filtration process) Basement membrane is made up of a network of collagen fibres and other proteins that make up a second sieve Most of the plasma contents can pass through the basement membrane but the Blood cells and many proteins are retained in the capillaries because of their size

Question 226

C15)How does the walls of the Bowmans capsule act as an additional filter

Answer 226

The walls of the Bowmans capsule have Special cells called podocytes acts as another filter, also have extensions called pedicels That wraparound capillaries forming slits that make sure any cell, platelets or large plasma proteins that have managed to get through the epidermal cells and the basement membrane do not get through into the tubule its self The filtrate which enters the capsule contains the same concentration of substances as they are in the blood plasma

Question 227

C15) What is the importance of reabsorption in the kidneys

Answer 227

Ultrafiltration removes urea, The waste product of protein breakdown from the blood but also removes a lot of water along with other substances which are present in the plasma, many of which are needed by the body The ultrafiltrate is also less concentrated than the blood plasma The main function of the nephron after the Bowmans capsule is to return most of the filtered substances back to the blood

Question 228

C15) what is the importance of the proximal convoluted tubule in reabsorption of substances

Answer 228

In the proximal convoluted tubule all the glucose, amino acids, vitamins and hormones are moved from the filtrate back into the blood by active transport Around 85% of sodium chloride and water is reabsorbed as well-sodium ions are moved by active transport, chloride ions and water follow passively down concentration gradients Once the substances have been removed from the nephron, they diffuse into the extensive capillary network surrounding the tubules down a steep concentration gradient maintained by the constant flow of blood through the capillaries The filtrate reaching the loop of Henley at the end of the proximal convoluted tubule is At the same concentration as the tissue fluid and the blood 80% of The glamorous filtrate has been reabsorbed into the blood, remains the same regardless of the conditions in the body

Question 229

C15) what are the adaptations of the cells lining the proximal convoluted tubule

Answer 229

Covered with microvilli, greatly increases the surface area over which substances can be reabsorbed They have many mitochondria to provide the ATP needed in active transport systems

Question 230

C15) what is the importance of the loop of Henle for the reabsorption of substances into the blood

Answer 230

The loop of Henle is the section of the kidney tubule that enables mammals to produce urine more concentrated than their own blood Different areas of the loop have different permeability to water and this is central to the way the loop of Henle functions Counter current multiplier, using energy to produce concentration gradient that result in the movement of substances such as water from one area to another Cells use ATP to transport ions using active transport, produces a diffusion gradient in the medulla Changes that take place in the descending limb of the loop of Henle depends on the high concentrations of sodium and chloride ions in the tissue fluid of the Madella which are the results of events in the ascending limb of the loop

Question 231

C15) how does the descending limb of the loop of Henley help with reabsorption of substances

Answer 231

The descending limb leads from the proximal convoluted tubule The region where water moves out of the filtrate down a concentration gradient. The lower part of the descending limb is permeable to water and run down into the medulla. Concentration of sodium and chloride ions in the tissue fluid of the Madella get higher and higher moving through from the cortex to the pyramids because of the ascending limb of the loop. The filtrate entering the descending limb of the loop is isotonic with blood, As it travels down the limb water passes out into the tissue fluid by osmosis down a concentration gradient. Then move down the concentration gradient into the blood of the surrounding capillaries Descending limb is not permeable to sodium and chloride ions and no active transport takes place in the descending limb The fluid that reaches the hairpin bend is very concentrated to the blood in the capillaries

Question 232

C15) how does the ascending limb of the loop of Henley help with reabsorption of substances

Answer 232

The first section of the ascending limb of the loop is very permeable to sodium and chloride ions and they moved out of the Concentrated solution by diffusion down a concentration gradient The second section of the ascending limb, sodium and chloride ions are actively pumped out into the medulla tissue The ascending limb of the loop is impermeable to water, water cannot follow the chloride and sodium ions down a concentration gradient Means the fluid left in the ascending limb becomes increasingly diluted, while the tissue fluid in the medulla develops the very high concentration of ions, essential for the kidney to produce urine The dilute fluid reaches the top of the ascending limb it is Less concentrated to the blood and enters the distal convoluted tubule and collecting duct

Question 233

C15) what is the importance of the distal convoluted tubule in the reabsorption of substances

Answer 233

Balancing the water needs to the body takes place in the distal convoluted tubule and the collecting ducts The areas where the permeability of the walls of the tubules varies with the levels of ADH The walls lining the distal convoluted tubule also have many mitochondria ,adapted to carry out active transport If the body lacks salt, sodium ions will be actively pumped out of the distal convoluted tubule with chloride ions following them down an electrochemical gradient. Water can also leave the distal convoluted tubule, Concentrating the urine, if the walls of the tubule are permeable in response to ADH Also plays a role in balancing the pH of the blood

Question 234

C15) what is the importance of the collecting duct for the reabsorption of substances

Answer 234

The collecting duct passes down through the concentrated tissue fluid of the renal medulla Main site where the concentration and volume of the urine produced is determined Water moves out of the collecting duct by diffusion down a concentration gradient as it passes through the renal medulla, urine becomes more concentrated Means water can be removed from the collecting duct all the way along its length, producing very hypertonic urine when the body needs to conserve water Permeability of the collecting duct to water is controlled by the levels of ADH determining how much or little water to reabsorb

Question 235

C15) what is Osmoregulation

Answer 235

The water potential of the blood has to be maintained regardless of the water and salt taken in as you eat or drink, and the water and mineral salts lost by sweating in defecation and in the urine Changing the concentration of urine is critical in this dynamic equilibrium The amount of water loss in the urine is controlled by antidiuretic hormone in a negative feedback system Antidiuretic hormone is produced by the hypothalamus and secreted into the posterior pituitary gland, where it is stored. ADH increases the permeability of the distal convoluted tubule and the collecting duct to water

Question 236

C15) What is the mechanical action of ADH

Answer 236

ADH is released from the pituitary gland and carried in the blood to the cells of the collecting duct where it has its effect The hormone does not cross the membrane of the tubule cells-binds to receptors on the cell membrane and triggers the formation of cyclic AMPAs a secondary messenger inside the cell A secondary messenger is a molecule which relates signal is received at cell-surface receptors to molecules inside the cell

Question 237

C15) what are the events caused by cAMP in response to ADH in the nephron

Answer 237

Vesicles in the cells lining the collecting duct fuse with the cell surface membrane on the side of the cell in contact with the tissue fluid of the medulla The membrane of these Vesicles contains protein-based water channels aquaporinsWhen inserted into the cell surface membrane they make it permeable to water Provides a route for water to move out of the tubule cells into the tissue fluid of the Madella and blood capillaries by osmosis

Question 238

C15)What happened when more ADH is released

Answer 238

The more ADH that is released the more water channels are inserted into the membrane of the Tubule cells, making it easier for more water to lead the tubule by diffusion resulting in the formation of a small amount of very concentrated urine Water is returned to the capillaries, maintaining the water potential of the blood and therefore the tissue fluid of the body

Question 239

C15) what happened when ADH levels full

Answer 239

Levels of cAMP Full, then the water channels are removed from the tubule cells membranes and enclosed in Vesicles again. The collecting duct become impermeable to water once more, So no water can leave Results in the production of large amounts of very dilute urine and maintains the water potential of the blood and tissue fluid

Question 240

C15) what is the negative feedback system of Osmoregulation

Answer 240

Permeability of the collecting duct is controlled to match the water requirements of the body very closely Brought about by a complex negative feedback system that involves Osmo receptors in the hypothalamus of the brain What’s the receptors are sensitive to the concentration of inorganic ions in the blood and are linked to the release of ADH

Question 241

C15)What happened when water is in short supply

Answer 241

The concentration of inorganic ions in the blood rises and the water potential of the blood and tissue becomes more negative Detected by the Osmoreceptors in the hypothalamus. They send nerve impulses to the posterior pituitary which intern releases stored ADH into the blood ADH is picked up by receptors in the cells of the collecting duct and increases the permeability of the tubules to water Water leaves the filtrate in the tubules and passes into the blood in the surrounding capillary network Small volume of concentrated urine is produced

Question 242

C15) what happens if there is an excess of water

Answer 242

The blood becomes more dilute and its water potential becomes less negative The changes detected by the Osmo receptors in the hypothalamus Nerve impulses in the pituitary gland are reduced or stopped and so the release of ADH by the pituitary is inhibited Very little reabsorption of water can take place because the walls of the collecting duct remain impermeable to water A large amount of dilute urine is produced

Question 243

C15) why is urine samples a good diagnosis test

Answer 243

It contains the breakdown particles of a whole range of chemicals, including hormones and any toxins within the body If you are affected by a number of different diseases new substances will show up in your urine

Question 244

C15) how is your urine used on a pregnancy test

Answer 244

The human embryo implants in the uterus. The site of the developing Potente then begins to produce a chemical called human chronic Gonadotrophin Some of this hormone is found in the blood and urine of the mother Modern pregnancy test for HCG in the urine but they rely on monoclonal antibodies

Question 245

C15) how is monoclonal antibodies made

Answer 245

Monoclonal antibodies are antibodies from a single clone of cells that all produce target particular cells or chemicals in the body A mouse is injected with HCG so it makes appropriate antibodies. The B cells make the required antibodies are then removed and fused with a a cancer cell which divides very rapidly Reproduce rapidly, resulting in a clone of millions of living factories making the desired antibody These monoclonal antibodies are collected and purified and used in a variety of ways

Question 246

C15) what are the main stages in a pregnancy test

Answer 246

The wick is soaked in the first urine passed in the morning this will have the highest levels of HCG The test contains mobile monocultural antibodies that have very small coloured beads attached to them. They will only bind to HCG.If the woman is pregnant then HCG in her Urine binds to the mobile Monoclonal antibodies and former HCG antibody complex The urine carries on along the test structure until it reaches a window Here there are immobilised monoclonal antibodies arranged in a line that only binds to the HCG antibody complex. If the woman is pregnant a coloured line appears in the first window The urine continues up the rest of the test to the second window, here there is usually a line of immobilised monoclonal antibodies that only bind to the mobile antibodies, Regardless of whether they are bound to HCG. The coloured line forms regardless of whether the woman is pregnant, simply indicates that the test is working

Question 247

C15) How is anabolic steroids detected in urine

Answer 247

Athletes and bodybuilders may try to cheat by using anabolic steroids Anabolic steroids are drugs that mimic the action of the male sex hormone test Testerone and they stimulate the growth of muscles They are excreted in the urine, by testing the urine scientist can you show that an individual has been using these drugs The urine sample is vaporised with a solvent and passed along a tube and is analysed by a chromatogram

Question 248

C15) how is urine used for drug testing

Answer 248

Urine is tested for the presence of different drugs because drugs or metabolites, the breakdown product of drugs are filtered through the kidneys and stored in the bladder, therefore drug traces can be found in the urine sometime after the drug was used The first sample may be tested using monoclonal antibodies to bind to the drug, the second sample may be run through a gas chromatograph

Question 249

C15) what are the causes of kidney failure

Answer 249

Kidney infection The structure of the podocytes and the tubules themselves may be damaged or destroyed Raised blood pressure that can damage the structure of the epithelial cells and basement membrane of the Bowmans capsule Genetic diseases such as polycystic kidneys where the tissue is replaced by fluid filled cysts

Question 250

C15) What may happen as a result of high blood pressure in the kidneys

Answer 250

Protein in the urine – the basement membrane of the Bowmans capsule are damaged, they no longer act as filters and large plasma proteins can pass into the filtrate and is passed out in the urine Blood in the urine- another symptom that the filtering process is no longer working

Question 251

C15) what are the effects of complete kidney failure

Answer 251

Loss of electrolyte balance- the kidneys fail, the body cannot excrete excess sodium, potassium and chloride ions causing an osmotic imbalance in the tissues and eventually death Buildup of excess urine in the blood- the kidneys fail, the body cannot get rid of urine and it can poison the cells High blood pressure- the kidneys play an important role in controlling the blood pressure by maintaining the water balance of the blood. Therefore if they fail the blood pressure increases and can cause a range of problems Weakened bones as the calcium/phosphorus imbalance in the blood is lost Anaemia – the kidneys are involved in the production of a hormone Which stimulates the formation of red blood cells. When the kidneys fail it can reduce the production of red blood cells

Question 252

C15) what is the glomerular filtration rate

Answer 252

Kidney problems almost always affect the rate at which blood is filtered in the Bowmans capsule of the nephrons The glamorular Filtration rate is widely used as a measure to indicate kidney disease The rate of filtration is not measured directly a sample blood test measure the levels of creatinine In the blood. creatinineIs a breakdown product of muscles and it is used to give an estimate glamerular filtration rate If the levels of creatinine in the blood goes up it is a signal that the kidneys are not working properly

Question 253

C15) what factors need to be taken into account when calculating GFR

Answer 253

GFR decreases steadily with age even if you are healthy Men usually have more muscle mass and therefore more creatinine than women

Question 254

C15) What are the treatment options for kidney failure

Answer 254

Normal GFRs do not fall below 70 even in very elderly people. GF all of below 60for more than three months is taken as an indicator of moderate to severe chronic kidney disease and if it is below 15, kidney failure Two main ways in which kidney failure is treated. In renal dialysis the functions of the kidney is carried out artificially, in a transplant a new healthy kidney is put into the body to replace the functions of the failing kidney Two main type of dialysis -Haemodialysis and peritoneal dialysis

Question 255

C15) what is haemodialysis

Answer 255

Involves a dialysis machine, carried out in hospital sometimes patients will have a machine in their home. Blood leaves the patient’s body from an artery and flows into the dialysis machine between partially permeable dialysis membranes. These membranes mimic the basement membrane of the Bowmans capsule On the other side of the membrane is the dialysis fluid. During dialysis it is important that patients lose the excess urine and mineral ions that have built up in the blood,Equally important not to lose a useful substances such as glucose and some mineral ions. The loss of these substances is prevented by careful control of dialysis fluid The blood and the dialysis fluid flow in opposite directions to maintain a counter current exchange system and maximise exchange that takes place The whole process of dialysis depends on a diffusion down a concentration gradient there is no active transport Dialysis takes about eight hours and has to be repeated regularly. Also need to manage their diet carefully eating relatively low protein and salt and monitoring the fluid intake to keep the blood chemistry a stable as possible

Question 256

C15) what is in dialysis fluid

Answer 256

Contains normal plasma levels of glucose to ensure there is no net movement of glucose out of blood Also contains normal levels of mineral ions, so any excess mineral ions in the blood move out by diffusion down a concentration gradient into the dialysis fluid therefore restoring electrolyte balance Dialysis fluid contains no urea meaning there is a very steep concentration gradient from the blood to the fluid as a result urea leaves the blood

Question 257

C15)What is peritoneal dialysis

Answer 257

Dialysis done inside the body- makes use of the natural dialysis membrane formed by the lining of the abdomen, the peritoneum Done at home and the patient can carry on with their normal life while it takes place The dialysis fluid is introduced into the abdomen using a catheter, The fluid is left for several hours for dialysis to take place across the peritoneal membrane Urea and excess mineral ions pass out of the blood capillaries into the tissue fluid and out across the peritoneal membrane into the dialysis fluid. The fluid is then drained off and discarded leaving the blood balanced again and the urea and excess minerals removed

Question 258

C15) How is kidney failure treated by transplant

Answer 258

Long-term dialysis has some serious side-effects Best solution is a kidney transplant, where a single healthy kidney from a donor is placed within the body. The blood vessels are joined and the day ureter Of the new kidney is inserted into the bladder. If the transplant is successful the kidney will function normally for many years

Question 259

C15)What is one of the main problems associated with transplanted organs

Answer 259

The risk of rejection The antigens on the donor organ differ from the antigens on the cells of the recipient and the Muinn system is likely to recognise this resulting in rejection and destruction of the new kidney Transporting organs don’t last forever with an average transplanted kidney functioning for around 9 to 10 years although some continue working for around 50 years

Question 260

C15) what are some ways to reduce the risk of rejection of transplanted organ

Answer 260

The match between antigen of the donor and the recipient is made as close as possible The recipient is giving drugs to suppress their immune response for the rest of their lives. Helps to prevent the rejection of the new organ immunosuppressant drugs are improving all the time and the need for a really close tissue match is becoming less important

Question 261

C15) what are the disadvantages of taking immunosuppressant drugs

Answer 261

Prevents the patients from responding effectively to infectious diseases They have to take great care if they become ill in anyway

Question 262

C15)What is better dialysis or transplant

Answer 262

Dialysis is much more readily available than donor organs. Enabling the patient to lead a relatively normal life. However patients have to monitor their diet carefully and need regular sessions on the machine Long-term dialysis is much more expensive than a transplant and can eventually cause damage to the body Transplant patients are free from restrictions which come with regular dialysis sessions and dietary monitoring The main source of Donna kidney is from people who died suddenly. Unfortunately Four people needing a transplant there is a shortage of kidney donors. Many people do not register as donors. Decreasing potential donors

Question 263

C16) what is the meaning of the tropisms

Answer 263

Also show directional growth in response to environment clues such as light and gravity

Question 264

C6) what is the coordination of plants like

Answer 264

Limitation is that they are not mobile and do not have a rapid responding nervous system The timescale for most plant responses are slower than animal responses but they still respond as a result of complex chemical interactions Plants have evolved a system of hormones - chemicals produced in one region of the plant and transported both through the transports tissues and from cell to cell and have an affect in another part of the plant Important plant hormones include auxins,Gibberellins, abscisic acid and ethene

Question 265

C16)What are the roles of auxin in plants

Answer 265

Control cell elongation Prevent leaf fall Involved in tropism Stimulate the release of Ethene Involved in fruit ripening

Question 266

C16) What are the roles of gibberellin in plants

Answer 266

Cause Stem elongation Trigger the mobilisation of food stores in a seed add germination Stimulate pollen tube growth in fertilisation

Question 267

C16) What are the roles of ethene in plants

Answer 267

Causes fruit ripening Promotes leaf fall (abscission) in deciduous trees

Question 268

C16) What are the roles of abscisic acid in plants

Answer 268

Maintains dormancy of seeds and buds Stimulates cold Protective responses Stimulates stomatal closing

Question 269

C16) What is the importance of plant hormones

Answer 269

Plants produce chemicals which signal to other species, to protect themselves from attack by insect pests for example,And may communicate with other plants. Also produce chemical defences against herbivores The growth of plants from the germination of the seed to long term growth of the tree is controlled by plant hormones

Question 270

C16) why are scientists still unsure about the details of plant responses

Answer 270

Plant hormones work at very low concentrations, so isolating them and measuring changes in concentration is not easy Multiple interactions between the different chemical control systems also make it very difficult for researchers to isolate the role of a single chemical in a specific response

Question 271

C16)What are the plant responses involved in seed germination

Answer 271

When the seed absorbs water, the embryo is activated and begins to produce gibberellin They intern stimulate the production of enzymes that break down the food stores found in the seeds. The food store is in the cotyledons in dicots seeds and the endosperm in monocot seeds The embryo plant use these food stores to produce ATP for building materials so it can grow and break through the seed coat Evidence suggests that gibberellins switches on jeans which code for amylase and protease- the digestive enzymes required for germination. Evidence suggest that Another plant hormone, abscisic acid, Acts as an antigonist to gibberellins (interferes with the action of gibberellin) It is the relative level of both hormones which determine when A seed germinates

Question 272

C16) What is the evidence to suggest the role of gibberellins in the germination of seeds

Answer 272

Mature varieties of seeds have been bred which lacked the gene that enables them to make gibberellins. The seeds do not germinate. If gibberellin was applied to the seeds externally then they germinate a normally If gibberellins biosynthesis inhibitors are applied to seeds, they do not germinate as they cannot make the job really needed for them to break dormancy. If the inhibitor is removed or the gibberellins are applied the seeds germinated

Question 273

C16) what are Auxins

Answer 273

Auxins or growth stimulant produced in plants They are made in cells at the tip of the shoots and roots and in the meristem Auxins can move down the stem and up the root both in the transport tissue and from cell to cell The effects of auxin depends on the concentration and any interaction it has with other hormones

Question 274

C16) how does auxin stimulate the growth of apical shoot

Answer 274

Awesome effects the plasticity of the cell wall-the presence of oxygen means the cell wall stretches more easily Auxin molecules bind to specific receptor sites in the plant cell membrane causing a fall in the pH to about five The optimal pH for the enzymes needed to keep the walls very flexible and plastic allowing cells to expand as they absorb water. Vacuoles get bigger and cell wall stretch As the cell mature, oxygen is destroyed. As the hormone levels for the pH rises so the enzymes maintaining plasticity become inactive. As a result of the cell wall becomes rigid and more fixed in shape and size and the sale can no longer expand and grow

Question 275

C16) how does apical dominance occur

Answer 275

High concentrations of auxins suppress the growth of lateral shoots resulting in apical dominance Growth in the main shoot is stimulated by the axon produced at the tip so it grows quickly The lateral shoots are inhibited by the hormone that moves back down the stem, so they do not grow very well Further down the stem, the auxin concentration is lower and so the lateral shoots grow more strongly

Question 276

C16) what is the evidence to suggest apical dominance is caused by auxin concentration

Answer 276

If the apical shoot is removed, the auxin producing cells are removed and so there is no auxin As a result, the lateral shoots, freed from the dominance of the apical shoots should grow faster If Auxin is applied artificially to the cut apical shoot, apical dominance is reasserted and lateral shoots growth is suppressed

Question 277

C16) how does root growth occur

Answer 277

Low concentrations of auxin promote root growth Up to a given concentration, the more auxin that reaches the root the more they grow Auxin is produced by the root tips and auxin also reaches the roots in low concentrations from the growing shoots If the apricot shoot is removed, then the amount of auxin reaching the roots is greatly reduced and root growth slows and stops Replacing the auxin artificially at the cut apricot shoot restores the growth of the roots High auxin concentration inhibits root growth

Question 278

C16) What is the importance of gibberellin

Answer 278

Involved in the germination of seeds Also important in the elongation of plant stems during growth Gibberellins affects the length of the internodes- the regions between the leaves on a stem Plants that have short stems produced few or no gibberellins

Question 279

C16) how did scientist discovered gibberellin and its affect

Answer 279

Was discovered because they were produced by a fungus that affected rice The infected seedlings grow extremely tall and thin Scientists investigated the right and isolated chemicals-gibberellins-which produce the same growth in the plant Then discovered that plants themselves produce the same compounds Scientists have bred many varieties of plants where the gibberellins synthesis pathway is interrupted Without gibberellins the plants stems are much shorter

Question 280

C16) what is the meaning of Synergism

Answer 280

If different plant hormones work together complimenting each other and giving a greater response than they would on their own.

Question 281

C16) what is the meaning of antagonism

Answer 281

If the substances have opposite effect, The balance between them will determine the response of the plant

Question 282

C16) why does deciduous trees lose their leaves

Answer 282

Plants that grow in temperature claimants experience great environment changes during the year For example the range of daylight and the temperature As light and temperature affect the rate of photosynthesis, seasonal changes have a big impact on the amount of photosynthesis possible The point comes when the amount of glucose required for respiration to maintain the leaves and to produce chemicals from chlorophyll that might protect them against freezing is greater than the amount of glucose produced by photosynthesis. A tree that is in leaf is more likely to be damaged or blown over by winter gales. Deciduous trees lose all of the leaves in the winter and remain dormant until the day is lengthen and temperature rises again in spring

Question 283

C16) how are plants light-sensitive

Answer 283

Plants are sensitive to a lack of light in the environment this is known as photoperiodism The lack of light is the cause for change The sensitivity of plants today laid results from a photosynthetic pigment called Phytochrome. This exists in two forms- Pr and Pfr. Each absorbs a different type of light and the ratio of Pr to Pfr changes depending on the levels of light

Question 284

C16) how does Abcission

Answer 284

The lengthening of the dark period triggers a number of changes including obscission and a period of dormancy during the winter months The falling light levels result in falling concentration of oxygen. The leaves respond to the falling auxins concentration by producing the gassiest plant hormone ethene. At the base of the lease stock is a region called the abscission zone, which is made up of two layers of sensitive cells to Ethan. Ethan seems to initiate gene switching in the cells resulting in the production of new enzymes, which digestion weaken the cell walls in the outer layer of the obscission Zone called the separation layer

Question 285

C16) What happened to the vascular bundle when Abcission happens

Answer 285

Vascular bundle which carries material into and out of the leaf are sealed off. At the same time fatty material is deposited in the cells on the stem side of the separation layer This layer forms a protective seal when the leaf falls, Preventing the entry of pathogens Cells deep in the separation zone respond to hormonal queues by retaining water and swelling, putting strain on the already weakened outer layer When further abiotic factors such as low temperature or strong autumn winds finish the process the strain is too much and the leaf separates from the plant

Question 286

C16) how do plants prevent freezing

Answer 286

If cells freeze, membranes are disrupted and they will die Many plants have evolved mechanisms that protect their cells in freezing conditions. The cytoplasm of the plant cells and the sap in the vacuole contains solutes which lowers the freezing point Some plants produce sugar, polysaccharides, amino acids, which act as antifreeze to prevent the cytoplasm from freezing or protect the cell even if they freeze. These are only produced during the winter months Different genes are suppressed and activated in response to a strained fall in temperature along with a reduction in day length, to withstand frosty conditions. A strained spell of warm weather along with extended day length reverses the changes in spring

Question 287

C16) how is the opening and closing of the stomata in response to abiotic factors induced

Answer 287

Under the control of the hormone ABA The leaf cells appear to release ABA under abiotic stress causing stomatal closure The roots also provide an early warning of water stress through ABA For example, when the levels of soil waterfalls and transpiration is under threat, plant roots produce ABA which is transported to the leaves where it binds to receptors on the plasma membrane of the stomatal guard cells ABA activates changes in the ionic concentrations of the guard cells, reducing the water potential and therefore turgor of the cell. Therefore resulting in reduced turgor, The guard cells close the stomata and water loss by transpiration is Greatly reduced

Question 288

C16) what are the physical defences that plants have to have to herbivores

Answer 288

Thorns Berries Spikes Spiny leaves Hairy leaves

Question 289

C16) what are the chemical defences that plants have to herbivores

Answer 289

Tannins Alkaloids Terpennoids

Question 290

C16) what do Tannins do as a chemical defence mechanism for plants

Answer 290

Can make up 50% of the dry weight of the leaves They are toxic to insects andbind to the digestive enzymes produced in the saliva and inactivate them Tea and white wine are both rich in plant tannins

Question 291

C16) what do alkaloids do as a chemical defence mechanism against herbivores

Answer 291

Very bitter tasting, nitrogenous compounds found in plant Many of them act as a drugs, affecting the metabolic of animals that take them in and sometimes poisoning them Caffeine is toxic to fungi and insects and the caffeine produced by coffee bush seedlings spread through the soil and prevents the germination of seeds of other plants, so caffeine protects the plant both against herbivores and against plant rivals Nicotine is a toxin produced in the roots of tobacco plants, transported to the leaves and stored in vacuoles to be released when eaten

Question 292

C16) what are the effects of Terpenoids as a chemical defence against herbivores

Answer 292

Which often form essential oils but also often act as toxins to insects and fungi that might attack the plant

Question 293

C16) what are pheromones

Answer 293

Is a chemical made by an organism which attracts the social behaviour of other members of the same species. Because plants do not behave socially, they do not rely on loads of pheromones

Question 294

C16) what is an example of pheromones being used by plants to defend themselves

Answer 294

There is some evidence that plants communicate by chemicals produced in the root system and that one plant can tell a neighbour if it is underwater stress

Question 295

C16) what are volatile organic compounds

Answer 295

They act like pheromones between themselves and other organisms particularly insects They diffuse through the air in and around the plant plants use these chemical signals to defend themselves. Usually only made when the plant detects attack by an insect pest through chemicals in the saliva of the insect Sometimes a volatile organic compound produced by a plant that has been attacked will not only attract predators, it may also act as a pheromone so that neighbouring plants begin to produce volatile organic compounds before they are actually attacked

Question 296

C16) how did plants respond to touch

Answer 296

The plant mimosa pudica, If the leaf is touched they fall down and collapse Scientists think this frightened of large herbivores and dislodge a small insects which have landed on the leaves The leaf falls off in a few seconds and recovers over 10 to 12 minutes as a result of potassium ion movement into specific cells followed by osmotic water movement

Question 297

C16) What is the meaning of tropism

Answer 297

Plant growth responses to stimuli from one direction

Question 298

C16) what is phototropism

Answer 298

The growth of plants in response to light which comes from One Direction only

Question 299

C16) what is the meaning of geotropism

Answer 299

The response to gravity

Question 300

C16) how is tropism a response to the environment

Answer 300

To be able to make the maximum use of environmental conditions, plants must grow and respond to variations in these conditions The movement of the roots and shoots take place in direct response to environmental stimuli. The direction of the response is related to the direction from which the stimulus comes

Question 301

C16) how do you scientist do you research about tropisms

Answer 301

Research on tropisms use germinating seeds and very young seedlings because they are easy to work with and manipulate and they are growing and responding rapidly, any changes show up quickly Changes also tend to affect the whole organism rather than a small part and this makes any tropism is much easier to observe and measure

Question 302

C16)How does phototropism occur

Answer 302

Is the result of movement of auxins across the shoot or route if it is exposed to light that is stronger on one side than the other If plants are exposed to the light which is brighter on one side than another or two unilateral light that only shines from one side then the shoots of the plant will grow towards the light and the roots, if exposed will grow away. Shoots are said to be positively phototropic and the roots are said to be negatively phototropic. It insures that the shoots receive as much all-round light as possible allowing the maximum amount of photosynthesis to take place

Question 303

C16) what happens to the shoot when the tip is removed

Answer 303

No response because the tip must either detect the stimulus or produce the messenger as its removal prevents any response

Question 304

C16) what happened to the shoot when light proof cover is placed over in tact tip of shoot

Answer 304

No response because the tip must detect light stimulus

Question 305

C16) What happens to the shoot when a thin impermeable barrier of mica is placed on the side of the stimulus

Answer 305

The chemical moves on the shaded side and the shoot bends towards the light

Question 306

C16) What happens to the shoot when a thin impermeable barrier of mica is placed on the shaded side to the stimulus

Answer 306

Movement of chemical down shaded side is prevented by mica therefore there is no response

Question 307

C16) what is the response from a plant when the tip is removed then gelatin block is inserted and the tip is replaced

Answer 307

Movement of chemicals down the shaded side and the shoot bends towards the light this is because the gelatin allows chemicals to pass through it but not electrical messages, the bending which occurs must be due to a chemical passing from the tip

Question 308

C16) what are the effects of unilateral light

Answer 308

The side of a shoot exposed to light contains less auxin than the side which is not illuminated Appears that light causes the auxin to move laterally across the shoot, So there is greater concentration on on illuminated side, internal causing cell elongation and growth on the dark side resulting in observed growth towards the light The original theory was that light destroyed the auxin but this has been disproved by experiment showing that the levels of auxin in shoots are much the same regardless of whether they have been kept in the dark or unilateral light

Question 309

C16) how are plants grown in the dark

Answer 309

Plants grow upwards rapidly to reach the sunlight to be able to photosynthesise The ceiling that breaks through the soil first will not have to compete with other seedlings for light Evidence suggests that it is gibberellins that is responsible for the extreme elongation of the internodes when a plant is grown in the dark Once a plant is exposed to light, a slowing of upward growth is visible. Resources can be used for synthesising leaves, strengthening stems and growth proven by the fall of gibberellins when exposed to light

Question 310

C16) What is the response of a plant to geotropism

Answer 310

Plants always receive a unilateral gravitational stimulus- gravity always acts downwards Response of plants to gravity can be seen in laboratory using seedlings placed on their side either in all round light or in the dark. Shoots are usually negatively geotropic, grows away from the gravitational pull and roots arePositively geographic, grows towards gravitational pull. Adaptation ensures that the roots grow down into the soil and the shoots grow up to the light

Question 311

C16) how do plants control the ripening of fruits

Answer 311

The plant hormone ethene is involved in the ripening of climacteric fruits, fruits which can ripen after being harvested Ripening is linked to a peak of ethene produced triggering a series of chemical reactions including a greatly increased respiration rate Non-climacteric fruits do not produce large amount of ethene and do not ripen after being picked

Question 312

C16) how is Ethene used commercially to control ripening

Answer 312

Used for the production of perfectly ripe and climacteric fruit for greengrocers and supermarkets. Fruits are harvested when they are fully formed but long before they are ripe and then transported. The unripe fruit is hard and much less easily damaged during transportation around the world than the ripe version When the fruits are needed for sale they are exposed to ethene gas under controlled conditions so that each batch of fruit ripens at the same rate.

Question 313

C16) how does hormone rooting powder help horticulturists and agriculturists

Answer 313

Auxin affects the growth of both shoots and roots Scientists have discovered that the application of oxygen to cut shoots stimulates the production of roots Making it much easier to propagate new plants from plant cuttings. If cuttings are placed in compost roots may eventually appear and a new plant forces. Dipping the cut stem into hormone rooting powder increases the chances of roots forming and a successful propagation taking place

Question 314

C16)How does micropropagation help farmers

Answer 314

Many plants are now propagated on a large scale by micropropagation, when thousands of new plants are grown from a few cells of the original plant Plant hormones are essential in this process

Question 315

C16) how do hormonal weedkillers work

Answer 315

The interactions between different plant humans are finally balanced and able to plant to grow. If this balance is lost it can interrupt the metabolism of the whole plant and may lead to plant death Weeds interfere with crop plants competing for light, space, water and minerals Scientists have developed synthetic auxins which act as very effective weedkillers. Most of the weeds are broad leafed dicots, while staple foods are Narrow leafed monocots, so synthetic dicot auxins are applied as weedkillers and absorbed by the broad leafed plant and affects their metabolism, growth rate increases and becomes unsustainable, killing the plant. does not affect the Narrow leafed monocots

Question 316

C16) how are other plant hormones used commercially

Answer 316

Auxin can be used in the production of seedless fruit Ethan is used to promote fruit dropping in plants such as cotton, walnut and cherries Cytokines are used to prevent aging of ripening fruit and products such as lettuce Deborah Lynn can be used to delay ripening and aging in fruit, to improve the size and shape of fruits, and in the beer brewing to speed up the malting process