Topic 6 - Organisms Respond To Changes In Their Internal And External Environments

Question 1

Responses for survival

Answer 1

A stimulus is a detectable change in the environment.
These changes can be detected by receptors.
Organisms increase chance of survival by responding to stimuli via different response mechanisms.

Question 2

Tropism

Answer 2

When plants respond, via growth, to stimuli
Can be positive or negative, growing towards or away from stimulus
Controlled by specific growth factors (E.g. indoleacetic acid (IAA)
IAA - type of auxin, controls cell elongation in shoots and inhibits growth of cells in roots, made in tip or roots and shoots but can diffuse to other cells in

Question 3

Positive Phototropism

Answer 3

Shoots:
- light needed for LDR in photosynthesis, so plants grow and bend towards light (positive phototropism)
1. Shoot tip cells produced IAA, causing cell elongation
2. IAA diffuses to other cells
3. If there is unilateral light, IAA diffuses towards shaded side of shoot - results in higher concentration of IAA there
4. Cells on shaded side elongate more and results in plant bending towards light source

Question 4

Negative phototropism

Answer 4

Roots:
- don’t photosynthesise so don’t require light
- must anchor plant deep in the so8l
- high concentration of IAA inhibits cell elongation - causes roots cells to elongate more on lighter side and so root bends away from light.

Question 5

Negative Gravitropism

Answer 5

Shoots:
- IAA diffuses from upper side to lower side of shoot
- if plant is vertical, causes plant cells to elongate and plant grows upwards
- if plant on its side, cause shoot to bend upwards

Question 6

Positive Gravitropism

Answer 6

Roots:
- IAA moves to lower side of roots - upper side elongates and root bends down towards gravity and anchors plant

Question 7

Reflexes

Answer 7

Reflex - rapid automatic response to protect animals from danger
Reflex arc made of up three neurones - sensory, relay, motor
Rapid - only two synapses

Question 8

Simple Responses - Taxes and Kinesis

Answer 8

Keep organisms within favourable conditions of their environment (light, moisture, chemicals)
Taxes - move entire body towards favourable stimulus (positive taxis) or away from unfavourable stimulus (negative taxis)
Kinesis - changes speed of movement and rate it changes direction

Question 9

Receptors

Answer 9

Detect stimuli
Each receptor responds only to specific stimuli - stimulation leads to establishment of an action potential which can cause a response
Three receptors to know:
- pacinian corpuscle
- rods
- cones

Question 10

Pacinian corpuscle

Answer 10

• deep in skin, mainly in fingers and feet
• sensory neurons in pacinian corpuscle has special channel proteins in plasma membrane
• membranes have stretch-mediated sodium channels - open and allow Na+ to enter sensory neurons when stretched and deformed.
• when pressure is applied it deforms neurone plasma membrane, stenches and widens NA+ channels so it can diffuse in - leads to action potential

Question 11

Rods Cells

Answer 11

Process images in black and white
To create action potential, pigment of rod cells (rhodopsin) must be broken down into light energy
Detect light of very low intensity as many rod cells connect to one sensory neurone (retinal convergence) - means brain cannot distinguish between separate sources of light that stimulated it - low visual acuity

Question 12

Cone Cells

Answer 12

Process images in colour
Three types that contain different types of iodopsin pigment (red, green, blue) which all absorb different wavelengths of light
Iodopsin broken down if high light intensity - action potentials can only be generated with enough light
One cone cell connects to a bipolar cell - cones can only respond to high light intensity - why we can’t see colour in the dark
Connected to a bipolar cell - rain distinguish between separate sources of light - high visual acuity

Question 13

Distribution of Rods and Cones

Answer 13

Uneven distribution in retina
Light focused by lens on the fovea - receive highest light intensity
Most cone cells located near fovea
Rod cells further away

Question 14

Cardiac Muscle

Answer 14

Myogenic - it contracts on its own accord, but rate of contraction is controlled by wave of electrical activity (nervous system)

Question 15

Sinoatrial Node (SAN)

Answer 15

Located in right atrium
Known as the pacemaker

Question 16

Atrioventricular Node (AVN)

Answer 16

Located between right atrium and left ventricle within atria still

Question 17

What tissues run down the septum

Answer 17

Bundle of His

Question 18

What fibres are in the walls of the ventricles

Answer 18

Purkyne fibres

Question 19

Control of Heart rate

Answer 19

• SAN releases wave of depolarisation across the two atria, causing it to contract
• AVN releases another wave of depolarisation when first wave reaches it.Non- conductive layer between atria and ventricles prevents wave of depolarisation travelling down to ventricles
• instead, bundle of His, conducts the wave of depolarisation down the septum and the Purkyne fibres
• as a result, apex and walls of ventricles contract - short delay before this happens whilst AVN transmits second waves of depolarisation - allows enough time for atria to pump all blood into ventricles
• finally, the cells depolarise, and the cardiac muscle relaxes.

Question 20

Medulla Oblongata

Answer 20

In brain
Controls heart rate via the autonomic nervous system
Two pats:
- a centre linked to SAN to increase heart rate via sympathetic nervous system - release waves of depolarisation more frequently
- another that decreases heart rate via parasympathetic nervous system - release waves of depolarisation less frequently

Question 21

Homeostatic Control of Heart Rate

Answer 21

Heart rate changes in response to pH and blood pressure - stimuli detected by chemoreceptors and pressure receptors

Question 22

Myelinated Motor Neurone

Answer 22

The cell body of the neurone contains the organelles found in a typical animal cell. Proteins and neurotransmitter chemicals are made here

Question 23

Dendrites

Answer 23

Carry action potentials to surrounding cells

Question 24

Axon

Answer 24

Conductive, long fibre
Carries nervous impulse along motor neurone

Question 25

Schwann Cells

Answer 25

Wrap around axon to form myelin sheath - lipid so doesn’t allow charged ions to pass through it Gaps between myelin sheath called nodes of Ranvier

Question 26

Resting Potential

Answer 26

Neurone not conducting an impulse - difference between electrical charge inside and outside of the neurone More positive ions (Na+ and K+) outside compared to inside - inside of neurone more negative

Question 27

Establishing a Resting Potential

Answer 27

Maintained by sodium-potassium pump, involving active transport and ATP Pump moves 2 K+ ions in and 3 Na+ ions out Creates electrochemical gradient - causes K+ to diffuse out and Na+ to diffuse in

Question 28

Action Potential

Answer 28

Neurone’s voltage increases beyond a set point from the resting potential - generates nervous impulse Increase in voltage, or depolarisation, is due to neurone membrane becoming more permeable to Na+

Question 29

All-or-nothing principle

Answer 29

If depolarisation doesn’t exceed -55mV no action potential or impulse is produced (Nothing) Any stimulus that does exceed depolarisation of -55mV will always peak at the same max voltage. (All) Bigger stimuli increase frequency of action potentials Makes sure animals only respond to large enough stimuli

Question 30

Refractory Period

Answer 30

After action potential is generated, membrane enters refractory period when it can’t be stimulated because sodium channels are recovering and can’t be opened.

Question 31

Importance of Refractory Period

Answer 31

- ensures that discrete impulses are produced - action potentials can’t be generated one after another so this makes sure that each is separate - ensures that action potentials travel in one direction - stops action potential from spreading out in two directions which would prevent a response - limits number of impulse transmission - prevent over reaction to stimulus

Question 32

Factors affecting speed of conductance

Answer 32

Myleination and saltatory conduction Axon diameter Temperature

Question 33

Myelination and Saltatory conduction

Answer 33

Action potential jumps from node to node (saltatory conduction), which means action potentials travels along the axon faster

Question 34

Axon diameter

Answer 34

Wider diameter increases speed of conductance - less leakage of ions and therefore action potentials travels faster

Question 35

Temperature

Answer 35

Higher temperature increases speed of conductance because: - ions diffuse faster - enzymes involved in respiration work faster - more ATP for active transport in the sodium-potassium pump

Question 36

Synapses

Answer 36

Gaps between end of axon of one neurone and the dendrite of another Action potentials transmitted as neurotransmitters that diffuse across the synapse

Question 37

Function of synapse

Answer 37

- action potential arrives at synaptic knob. Depolarisation of knob leads to opening of Ca2+ channels and Ca2+ diffuses into synaptic knob - vesicles containing neurotransmitters move towards and fuse with Presynaptic membrane. Neurotransmitters released to synaptic gap. - neurotransmitters diffuse down concentration gradient across gap to post synaptic membrane. Neurotransmitters binds to receptors on surface of post synaptic membrane - Na+ ion channels on post membrane open and Na+ diffuse in, if enough neurotransmitters, then enough Na+ diffuse in, above threshold, and post-synaptic neuron becomes depolarised - Neurotransmitters degraded and released from receptor, the Na+ channel close and the post neuron reestablishes resting potential. Neurotransmitters transported back to Presynaptic neuron where they are recycled

Question 38

Neurotransmitter in Cholinergic Synapse

Answer 38

Acetylcholine Enzyme breaks acetylcholine back into Choline+Acetate

Question 39

Summation

Answer 39

Rapid build-up of neurotransmitters in synapse to help generate an action potential - spatial summation - temporal summation

Question 40

Spatial Summation

Answer 40

Many different neurones collectively trigger action potential by combining neurotransmitters they release to exceed threshold value

Question 41

Temporal Summation

Answer 41

One neurone releases neurotransmitter repeatedly over short period of time to add up to enough to exceed threshold value

Question 42

Inhibitory Synapse

Answer 42

- cause chloride ions to move into postsynaptic neurone and potassium ions to move out - makes membranes potential decrease to -80mV, hyperpolarisation - action potential unlikely

Question 43

Neuromuscular Junction

Answer 43

Synapse that occurs between a motor neurone and a muscle

Question 44

Similarity between Neuromuscular Junction and Cholinergic Synapse

Answer 44

Unidirectional due to neurotransmitter receptors only being on post synaptic membrane

Question 45

Differences between Neuromuscular Junction (NJ) and Cholinergic Synapse (CS)

Answer 45

- NJ only excitatory, CS both excitatory and inhibitory - NJ connects motor neurone to muscles, CS connects two neurones - NJ is end point for action potential, CS a new action potential is generated in next neurone - NJ acetylcholine binds to receptors on muscle fibre membranes, CS acetylcholine binds to receptors on Postsynaptic membrane of a neurone

Question 46

How do muscles act?

Answer 46

Muscles act in antagonistic pairs against an incompressible skeleton to create movement. Can be automatic as part of a reflex response or controlled conscious thought

Question 47

Myofibrils

Answer 47

Made up of fused cells that share nuclei and cytoplasm (sarcoplasm), and there is a high number of mitochondria Millions of myofibrils make up muscle fibres.

Question 48

Sarcomere

Answer 48

Two key proteins in myofibrils, myosin and actin, form a sarcomere

Question 49

Sliding Filament Theory

Answer 49

1. When an action potential reaches a muscle, it stimulates a response 2. Calcium ions enter and cause the protein tropomyosin to move and uncover the binding sites on actin 3. Whilst ADP is attached to myosin head, myosin heads to actin to form a cross-bridge 4. Angle created in cross-bridge creates tension - actin filament pulled and slides along the myosin. In doing so the ADP molecules are released. 5. ATP molecule binds to myosin head and cause shape to change - as a result it detaches from actin 6. Within sarcoplasm, enzyme ATPase which is activated by calcium ions, to hydrolyse ATP on myosin head into ADP and releases enough energy for myosin head to go back to original position 7. Entire process repeats continually whilst calcium ions remain Hugh and therefore muscle remains stimulated by nervous system

Question 50

ATP and Phosphocreatine

Answer 50

Active muscles need a high concentration of ATP The chemical phosphocreatine, which is stored in muscles, assists this by providing phosphate to regenerate ATP from ADP

Question 51

Difference in Structure between Slow and Fast twitch fibres

Answer 51

Slow-twitch fibres - contains large store of myoglobin, a rich blood supply and many mitochondria Fast-twitch fibres - thicker and more myosin filaments, large store of glycogen, a store of phosphocreatine to help make ATP from ADP, and a high concentration of enzymes involved in aerobic respiration

Question 52

Differences in Location between Slow and Fast twitch fibres

Answer 52

Slow-twitch fibres - calf muscles Fast-twitch fibres - biceps

Question 53

Differences in general properties between slow and fast twitch fibres

Answer 53

Slow-twitch fibres - contract slower and can respite aerobically for longer due to rich blood supply and myoglobin oxygen store. Muscles adapted for endurance work. Fast-twitch fibres - contract faster to provide short burst of powerful contraction. Muscles adapted for intense exercise like sprinting or weight lifting.

Question 54

Homeostasis

Answer 54

Homeostasis involves physiological control systems that maintain the internal environment within restriction limits. Important in maintaining - stable core temperature, stable blood pH in relation to enzyme activity

Question 55

Blood Glucose Concentration Changes

Answer 55

Increases - ingestion of food or drink containing carbohydrates Decreases - following exercise or if you have not eaten

Question 56

Pancreas Role in Blood Glucose Concentration

Answer 56

- Detects changes in blood glucose levels - Islets of Langerhans cells release insulin and glucagon to bring blood glucose back to normal

Question 57

Insulin Role in Blood Glucose Concentration

Answer 57

- released when blood glucose levels are too high. - causes a decrease in blood glucose levels

Question 58

Glucagon Role in Blood Glucose Concentration

Answer 58

- released when blood glucose levels are too low - causes increase in blood glucose levels

Question 59

Adrenaline Role in Blood Glucose Concentration

Answer 59

- released by adrenal glands when body anticipates danger - release results in more glucose being released from hydrolysis of glycogen in liver

Question 60

What happens when Blood Glucose level increases

Answer 60

1. Blood glucose levels increases 2. Detected by beta cells in the Islets of Langerhans (pancreas) 3. Beta cells release insulin 4. Liver cells become more permeable to glucose and enzymes activated to convert glucose to glycogen 5. Glucose removed from blood and stored as glycogen in cells 6. Normal blood glucose levels increases

Question 61

What happens when blood glucose levels decreases

Answer 61

1. Blood glucose levels decreases 2. Detected by alpha cells in Islets of Langerhans (pancreas) 3. Alpha cells release glucagon and Adrenal Gland release adrenaline 4. Second messenger model occurs to activate enzymes to hydrolyse glycogen 5. Glycogen hydrolysed to glucose and more glucose is released back into blood 6. Normal blood glucose levels

Question 62

How does Insulin decrease blood glucose levels

Answer 62

- attaching to receptors on surface of target cells - changes tertiary structure of channel proteins resulting in more glucose being absorbed by facilitated diffusion - more protein channels incorporated into cell membranes - more glucose absorbed from blood into cells - activating enzymes involved in conversion of glucose to glycogen - results in glycogenesis in liver

Question 63

How does glucagon increase blood glucose levels

Answer 63

- attaching to receptors on surfaces of target cells (liver cells) - when glucagon binds it causes protein to activate into adenylate cyclase and to convert ATP in molecule called cyclic AMP (cAMP). cAMP activates enzyme, protein kinase that can hydrolyse glycogen into glucose - activating enzymes involved in conversion of glycerol and amino acids into glucose

Question 64

Second Messenger Model

Answer 64

1. Glucagon binding to glucagon receptors 2. Once bound, causes change in shape to enzyme adenyl cyclase which activates it 3. Activated adenyl cyclase enzymes converts ATP into cyclic AMP (cAMP). cAMP is the second messenger model

Question 65

How does adrenaline increase blood glucose levels (second messenger model)

Answer 65

- adrenaline attaches to receptors on surface if target cells. Causes protein (G protein) to activate and convert ATP into cAMP. - cAMP activates enzyme that can hydrolyse glycogen into glucose - known as second messenger model of adrenaline and glucagon action, because the process results in formation of cAMP, which acts as a second messenger model

Question 66

Role of Liver

Answer 66

Glycogenesis - converting glucose into glycogen. Occurs in liver and is catalysed by enzymes Glycogenolysis - hydrolysis of glycogen to glucose. Occurs in liver due the second messenger model Gluconeogenesis - creating of glucose from other molecules such as amino acids and glycerol in the liver

Question 67

Type I diabetes

Answer 67

- unable to produce insulin - usually starts in childhood and could be the result of an autoimmune disease where beta cells are attacked - treatment involves injection of insulin

Question 68

Type II diabetes

Answer 68

- receptors on target cells lose responsiveness to insulin - usually develops in adults because of obesity and poor diet - controlled by regulating intake if carbs, increasing exercise and sometimes insulin injections

Question 69

Osmoregulation

Answer 69

- Controlling water potential of blood - hypertonic - blood with too low a water potential - hypotonic - blood with too high a water potential - crenation - too much water will leave cells and move into blood by osmosis. Cells will shrivel - lysis - too much water will move from blood into cells by osmosis. Cells will burst

Question 70

Hypertonic

Answer 70

- blood with too low a water potential - too much sweating, not drinking enough water, lots of ions in diet (lots of salt) Corrective mechanism - more water reabsorbed by osmosis into blood from the tubules of the nephrons. This means the urine is more concentrated as less water lost in the urine

Question 71

Hypotonic

Answer 71

- Blood with too high a water potential - drinking too much water, not enough salt in diet - Corrective mechanism - less water reabsorbed by osmosis into blood from the tubules of the nephrons. This means urine is more dilute and more water is lost in the urine.

Question 72

Structure of nephron

Answer 72

- long tubules surrounded by capillaries and there are around 1 million per kidney - osmoregulation occurs in nephrons in the kidneys - blood is filtered here to remove waste and selectively reabsorb useful substances back into the blood Structure: 1. Glomerulus - filters small solutes from the blood 2. Proximal Convoluted tubule - reabsorbed ions, water and nutrients, removes toxins and adjusts filtrate pH 3. Descending loop of Henle - aquaporins allow water to pass from filtrate into the interstitial fluid 4. Ascending loop of Henle - reabsorbed Na+ and Cl- from filtrate into interstitial fluid 5. Distal tube - selectively secretes and absorbs different ions to maintain blood pH and electrolyte balance 6. Collecting duct - reabsorbs solutes and water from filtrate

Question 73

Ultrafiltration

Answer 73

- occurs due to high hydrostatic pressure - water and small molecules are forced out of glomerulus capillaries into renal capsule

Question 74

Selective reabsorbtion

Answer 74

Occurs in proximal convoluted tubule

Question 75

Loop of Henle

Answer 75

Maintains sodium ion gradient so water can be reabsorbed into blood from the

Question 76

Distal convoluted tubule and Collecting duct to return

Answer 76

Water moves out of distal convoluted tubule and collecting duct to return to blood

Question 77

Collecting duct

Answer 77

Carries remaining liquid (urine) to the ureter

Question 78

Hypothalamus and posterior pituitary gland

Answer 78

- changes in water potential of blood are detected by osmoreceptors here - produces ADH - then moves to posterior pituitary and from here it is release into capillaries and into the blood

Question 79

Osmoreceptors

Answer 79

If water potential of blood is too low, water leaves the osmoreceptors by osmosis and they shrivel. This stimulates the hypothalamus to produce more of hormone ADH If water potential of blood is too high, water enters the osmoreceptors by osmosis. This stimulates the hypothalamus to produce less ADH

Question 80

ADH - Antidiuretic hormone

Answer 80

- causes increase in permeability of walls of collecting duct and distal convoluted tubule to water - causes more water to leave nephrons and be reabsorbed into the blood, so urine is more concentrated

Question 81

How does hypothalamus decrease water potential of blood

Answer 81

1. Wtaer potential of blood increases (too much water) 2. Detected by osmoreceptors in hypothalamus 3. Hypothalamus produces less ADH 4. Distal convoluted tubule and collecting duct walls become less permeable to water 5. Less water reabsorbed into blood and more is lost in urine (dilute urine) 6. Normal water potential of blood

Question 82

How does the hypothalamus increase water potential of blood

Answer 82

1. Water potential of blood decreases (not enough water) 2. Deeptected by osmoreceptors in hypothalamus 3. Hypothalamus produces more ADH - released into blood by posterior pituitary gland 4. Distal convoluted tubule and collecting duct walls become less permeable to water 5. More water reabsorbed into blood and less is lost in urine (concentrated urine) 6. Normal water potential of blood