survival and response

Question 1

what is a stimulus?

Answer 1

change in the internal/external environment that results in a response.

Question 2

what is an effector

Answer 2

muscle or gland that brings about the response.

Question 3

what is a receptor?

Answer 3

cell that detects a stimulus.

Question 4

What is taxis? Give detailed example

Answer 4

A directional movement in response to stimulus, eg earthworms move away from light

Question 5

What is kinesis? Give a detailed example

Answer 5

A random movement in response to stimulus, organisms will increase movement in unfavourable conditions and decrease in favourable conditions. Eg woodlice move more quickly in dry environments.

Question 6

Outline a method used to investigate how animals respond to changes in light.

Answer 6

A choice chamber. To investigate light – cover one half with black paper. Place 10 woodlice 5 mins record the number of woodlice in light in dark. Repeat/ share class results. Complete a chi square test

Question 7

define phototropism

Answer 7

: shoots grow towards the light to increase the rate of photosynthesis

Question 8

define gavitropism

Answer 8

shoots grow upwards and roots grow downwards towards the pull of gravity.

Question 9

What is the role of IAA in phototropism

Answer 9

IAA is produced by the cell in the tip of the shoot, IAA diffuses down the shoot

IAA accumulates on the shaded side of the stem, causing cell elongation

Shoot bends towards the light

Question 10

Explain gravitropism in flowering plants

Answer 10

The response of a horizontally growing root to gravity:

Cells in the tip of the root produce IAA, which is then transported along the root. Initially it is transported to all sides of the root.

Gravity influences the movement of IAA from the upper to lower side of the root.

A greater concentration of IAA builds up on the lower side of the root.

IAA inhibits cell elongation so the cells on this side elongate less and the root bends down.

Question 11

Consider the following facts about IAA:

They are easily synthetically made

They are readily absorbed by plants

They are not easily broken down

They are lethal to some plants in low concentrations

Narrow-leaved plants are less easily killed than broad leaved plants

Suggest ways in which these facts might be relevant to agricultural practice

Answer 11

As they are easily synthetically made and readily absorbed by plants and lethal to some plants in low concentrations makes them useful as herbicides. Narrow-leaved plants are less easily killed than broad leaved plants means that they will kill weed but not crops as they are usually broad leaved. AS they are not easily broken down means that they will stay in the soil and act as a selective weed killer for some time. possible danger could be that as it is not broken down for some time the soil may not be suitable for growing crops for some time or it could pass through the food chain.

Question 12

What is the autonomic nervous system and how does it work?

Answer 12

The autonomic nervous system is made up of the motor neurones which carry impulses to the involuntary muscles. Involuntary muscles are those over which we generally have no conscious control e.g. cardiac muscle, iris of the eye, gut muscles, muscles in arterioles.

There are two branches of the autonomic nervous system; the sympathetic and parasympathetic. The two branches are antagonistic which means they work in opposition to one another.

Under normal circumstances impulses travel along both branches simultaneously at a low rate but in times of stress the rate of impulses increases in the sympathetic branch and at times of relaxation the rate of impulses is higher in the parasympathetic.

Question 13

State the difference in function between a sensory neurone and a motor neurone.

Answer 13

Sensory neurone transmits nerve impulse from a receptor to the CNS; Motor neurone transmits nerve impulse from CNS to an effector

Question 14

What is an axon?

Answer 14

Axon carries the nerve impulse away from the cell body to an effector;

Question 15

Why do membranes need special channels for the diffusion of charged ions?

Answer 15

Charged ions cannot dissolve in a phospholipids bilayer membrane like that of the axon. Therefore they cannot diffuse across the membrane. The ions need channel protein to produce a hydrophilic channel for diffusion or facilitated diffusion.

Question 16

Explain why a neurone is active while it is said to be resting.

Answer 16

While the neurone is at rest, or not conducting an action potential, the membrane is actively transporting sodium ions out of the cell and potassium ions into the cell.

Question 17

How is the resting potential of a neurone maintained?

Answer 17

Actively transporting 2x Potassium ions into and 3x Sodium ions out of the axon establishes the resting potential using a sodium-potassium ion pump;

the resting potential is maintained by the movement of potassium ions out of the axon via potassium ion leakage channels, by facilitated diffusion;

negatively charged proteins inside the axon

-70mV

Question 18

List the events that results in an action potential

Answer 18

Voltage gated sodium channels open; sodium ions diffuse in down a diffusion gradient;

potential difference across the membrane is reversed +40mV gated sodium channels close and voltage gated potassium channels open and potassium diffuses out of the cell – the potential difference across the membrane reverses.

Question 19

Distinguish between depolarisation and hyperpolarisation.

Answer 19

Depolarisation – the potential difference across the membrane becomes less negative inside compared with outside;

Hyperpolarisation makes the potential difference across the membrane more negative inside compared to outside.

Question 20

Explain why it is impossible to stimulate another action potential in a cell membrane that is hyperpolarised.

Answer 20

The cell membrane has a greater potential difference across it than a normal resting potential (-80mV compared to -70mV). This makes it more difficult to depolarise the membrane. As sodium ions enter, the threshold that causes the sodium channels to open is not reached, therefore and action potential is not produced.

Question 21

How are the sodium ion channels opened?

Answer 21

Each channel has a voltage-sensitive gate. A change in the potential around the gate causes it to move or change shape. This opens the channel.

Question 22

Explain how diffusion gradients are created so that sodium ions can diffuse into the neurone.

Answer 22

The sodium/potassium ion pumps actively transport ions against their concentration gradients. Sodium ions are transported out of the neurone so that the concentration is low inside the neurone and high outside it. Potassium ions are transported into the neurone so that the potassium concentration is high inside the cell and low outside it.

Question 23

State the importance of a myelin sheath to the transmission of a nerve impulse.

Answer 23

Myelin sheath speeds up the transmission of a nerve impulse

Question 24

Explain how the myelin sheath causes saltatory conduction.

Answer 24

The myelin sheath is a fatty material bound to the neurone. The sodium and potassium ions cannot move through the sheath which is incomplete – the neurone membrane is exposed at the nodes of Ranvier, so the action potential jumps from one node to the next.

Question 25

Explain how the presence of a myelin sheath speeds up the movement of an action potential.

Answer 25

Impulses jump from node to node – gaps in the myelin sheath

Question 26

Explain how an action potential moves along a non myelinated neurone.

Answer 26

The membrane becomes depolarised ahead of the action potential.

Question 27

Explain how information about the strength of a stimulus reaches the brain.

Answer 27

By the number of cells responding to the stimulus and the frequency of action potentials from those cells.

Question 28

Explain what is meant by the term synapse and neurotransmitter.

Answer 28

A synapse is a functional contact between neurones; a neurotransmitter is a chemical that passes a signal from one neurone to another.

Question 29

List the sequence of events as a nerve impulse is transmitted across a cholinergic synapse.

Answer 29

Action potential arrives at the axon of the synapse. Ca+ channels open and Ca+ diffuse into the axon terminal. Synaptic vesicles containing the neurotransmitter diffuse to the presynaptic membrane, The vesicle fuses with the presynaptic membrane and releases neurotransmitter into the synaptic cleft. Neurotransmitter Achetylcholine diffuses across the synaptic cleft and binds to the receptors on the post synaptic cleft. This causes Na+ channels to open on the post synaptic membrane and sodium ions enter depolarising the post synaptic membrane. This initiates an action potential. The enzyme acetylcholine esterase breaks down the Ach, which is reabsorbed into the presynaptic knob – this requires energy in the form of ATP.

Question 30

Explain why the calcium channels need to be voltage gated.

Answer 30

The calcium channels have gates that respond to the voltage change caused by the original action potential. If the calcium ion channels responded to any other stimulus, the synapse would release transmitter substance at the wrong time.

Question 31

Why is it important that the synaptic cleft contains the enzyme acetylcholine esterase?

Answer 31

It must break down the neurotransmitter acetylcholine. If the Ach is left in the cleft it will continue to stimulate the postsynaptic neurone and cause action potentials.

Question 32

Suggest why the presynaptic neurone ends in a synaptic knob.

Answer 32

Provides a large surface area which allows more vesicles of Ach to be released and allows the presynaptic neurone to stimulate more than one postsynaptic neurone.

Question 33

List the roles played by synapses in the nervous system. 

Answer 33

Allows the transmission of one direction only from presynaptic to post synaptic membrane. May be excitatory or inhibitory. Allow spatial and temporal summation.

Question 34

Explain how a synapse can be inhibitory.

Answer 34

The neurotransmitter hyperpolarises the post synaptic membrane, so that the depolarisation is not sufficient to reach the firing threshold.

Question 35

Explain what is meant by the term summation

Answer 35

Summation is the additive effect of impulses at a synapse

Question 36

The cytoplasm in the synaptic knob has a high proportion of certain organelles. These include smooth endoplasmic reticulum, mitochondria and vesicles. Each organelle has a specific role to play in the functioning of the cell. Describe the role of these organelles and explain why they are found in relatively large numbers in the synaptic knob.

Answer 36

Smooth Endoplasmic reticulum – metabolism of neurotransmitter and with packaging it into vesicles. Vesicles contain the neurotransmitter ready for exocytosis into the cleft. Mitochondria – supply the ATP needed to recycle the Ach, making the vesicles and move them towards the presynaptic membrane.

Question 37

Demyelination is the loss of myelin from the neurones that are normally myelinated. Several degenerative diseases are due to the loss of myelin in certain neurones. The loss of muscle coordination faced by people with multiple sclerosis is due to the degeneration of the myelin sheath in neurones involved in the movement of muscles. The disease is suspected to be an autoimmune disorder – the immune system attacks the myelin sheath. The immune system may cause inflammation due to overproduction of cytokines or other factors such as interferon. What role do cytokines play in the immune system? Suggest how overproduction of cytokines could lead to inflammation and cell damage.

Answer 37

Cytokines are similar to hormones. They carry signals to certain cells in the immune system. They stimulate the action of macrophages, phagocytes, B lymphocytes and T kiler cells. If too much cytokine is released it may overstimulate the action of phagocytic cells and T killer cells which could cause damage too many body cells and produce inflammation

Question 38

What is a transducer?

Answer 38

to convert the change in form of energy by the stimulus into another form.

Question 39

Explain why sensory receptors are described as transducers.

Answer 39

They convert one form of energy into another.

Question 40

What is the difference between the gated channels in the generator region and those further along the neurone?

Answer 40

The gated channels in the generator region have gates that are operated by energy coming from the stimulus. In the remainder of the neurone the gates are operated by potential difference changes. The gates would be opened by the movement of ions in the local circuit or by changes in potential difference s the membrane becomes depolarised.

Question 41

List the different types of receptors found in mammals.

Answer 41

Photoreceptor; Electro receptor; mechanoreceptor; Thermoreceptor; chemoreceptor

Question 42

Describe how a named receptor is able to act as a transducer.

Answer 42

Photoreceptors convert light energy into electrical energy; Mechanoreceptors such as pressure receptors convert touch pressure into electrical energy; chemoreceptors such as taste buds convert chemical energy into electrical energy

Question 43

Describe the structure of a Pacinian corpuscle and explain how it works.

Answer 43

Pacinian corpuscle responds to mechanical pressure. The sensory neurone ending at the centre of the Pacinian corpuscle has a special type of sodium channel in its plasma membrane – stretch mediated sodium channel. These change the permeability of sodium ions when they are deformed. In its resting state, the stretch mediated sodium channels of the membrane are too narrow to allow sodium ions to pass through. When pressure is applied the Pacinian corpuscle becomes deformed and the membrane around the neurone becomes stretched. This stretching widens the sodium channels and allows sodium ions to diffuse into the neurone. This influx changes the potential and depolarises the membrane- producing a generator potential. Generator potential creates an action potential.

Question 44

Explain why brightly coloured objects appear grey in dim light.

Answer 44

Only rod cells are stimulated by low intensity light. Rod cells cannot distinguish between different wavelengths/ colours of light, therefore the object is perceived as a mixture of boack and white-grey.

Question 45

At night it is easier to see a star in the sky by looking slightly to the side of it rather than at it directly. Suggest why.

Answer 45

Light from star is low light intensity. Looking directly at the star, light gets focused on the fovea, where there are only cones. Cones respond to high light intensity. Looking at it from the side means that it gets focus on the retina where there are rod cells, these are stimulated at low light intensities so the star can be seen.

Question 46

Outline the chemical mechanism controlling the heart rate

Answer 46

Sinoatrial node (SAN) initiates a wave of excitement (electrical impulses). This spreads over the walls of the atria causing them to contract- atrial systole. The electrical impulses reach the atrioventicular node (AVN). The wave of excitement is delayed through this node which allows the complete contraction of the atria before the ventricles start to contract. The wave of excitement then travels down highly conductive tissue in the septum called the purkyne tissue/ bundle of His. As it reaches the base of the ventricles it causes the ventricles to contract from the bottom upwards. This is ventricular systole. The heart then goes into a period of relaxation called diastole

Question 47

Describe the function of the autonomic nervous system.

Answer 47

ANS controls the involuntary activities of internal muscles and glands

Question 48

Distinguish between the functions of the sympathetic and parasympathetic nervous system

Answer 48

SNS stimulates effectors and so speeds up activity; prepares for stressful situations eg the flight or fight response PNS inhibits effectors and slows down activity; controls activity under resting conditions, conserving energy and replenishing body reserves. Eg rest and digest

Question 49

Suppose the parasympathetic nerve connections from the medulla and oblongata to the SAN were cut. Suggest what might happen if a person’s blood pressure increases above normal.

Answer 49

Blood pressure remains high because the parasympathetic system is unable to transmit nerve impulses to the SAN (which decreases HR and would lower BP)

Question 50

The nerve connecting the carotid artery to the medulla oblongata of a person is cut. This person then undertakes some strenuous activity. Suggest and explain what might happen to the persons:

Answer 50

Heart rate – as the nerve is cut, no action potential can be sent to cardiovascular centre in medulla oblongata so HR remains the same as before exercise Blood carbon dioxide concentration. Blood CO2 concentration increases as a result of increased respiration- blood pH will lower and will be detected by chemoreceptors but as nerve is cut no action potential sent to cardiovascular centre in medulla oblongata so no increase in heart rate

Question 51

Outline the sequence of event that take place at a neuromuscular junction.

Answer 51

Impulse depolarises the pre-synaptic membrane Calcium channels open and calcium ions diffuse into the pre synaptic knob (motor end plate) Vesicles fuse with the membrane and release acetylcholine into the synaptic cleft Acetylcholine diffuses across the gap and binds to receptor proteins on the muscle cell membrane. The membrane becomes depolarised; the wave of depolarisation passes along the membrane and down the T tubules. Calcium ions are released from the sarcoplasmic reticulum Calcium ions cause tropomyosin to move away from the actin binding sites allowing the myosin heads to bind.

Question 52

List the similarities/differences between a synapse and neuromuscular junction.

Answer 52

Same: both have neurotransmitter in vesicles, which are released by exocytosis and which bind to receptor, this is then broken down in the synaptic cleft. Different: post synaptic membrane in neuromuscular junction have lots of folds which form clefts. These store AChE. The post synaptic has more receptors than other synapses. It is always excitatory

Question 53

What are antagonistic muscles? -

Answer 53

Pairs of muscles attached across a joint, which pull in opposite directions.

Question 54

Distinguish between flexor and extensor muscles

Answer 54

flexor bends a joint; extensor muscles straighten

Question 55

What muscular action is needed to flex the elbow? –

Answer 55

Contraction of the biceps and brachialis muscles, relaxation of the triceps.

Question 56

Explain why the elbow is described as a hinge joint

Answer 56

The movement of the joint operates in one plane only, much as the opening of a door around a hinge.

Question 57

Outline the mechanism of muscle contraction.

Answer 57

Action potential arrives at many neuromuscular junctions simultaneously, causing calcium ion protein channels to open and calcium ions to diffuse into the synaptic knob Ca2+. Cause synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine into the synaptic gap. Acetylcholine diffuses across the synaptic cleft and binds with receptors on the muscle sarcolemma causing depolarisation. Action potential travels down the T tubule and cause Ca2+ to be released from sarcoplasmic reticulum Ca2+ causes tropomyosin molecules that were blocking the binding site on the actin filament to pull away, unblocks binding site on the actin allowing actin myosin cross bridge to form. ADP molecules attached to the myosin head mean that they are in a state to bind to the actin filament and form a cross bridge Once attached to the actin filament, the myosin heads change their angle, pulling the actin filament along as they do so and releasing ADP and Pi .This is called the power stroke.. An ATP molecule attaches to the myosin head, causing it to detach from the actin filament The calcium ions then activate ATPase, which hydrolyses the ATD to ADP and Pi. The hydrolysis provides the energy for the myosin head to return to its original position. The myosin head, once more with an attached ADP molecule then reattaches itself further along the actin filament and the cycle is repeated as long as the concentration of calcium ions remains high.

Question 58

Explain how the shape of myosin molecule is adapted to its role.

Answer 58

Myosin has a globular head that is hinged, so can move back and forth. Each myosin head has a binding site for actin and a binding site for ATP

Question 59

Sprinters have high levels of phosphocreatine in the muscles. Explain the advantage of this.

Answer 59

Phosphocreatine stores the phosphate that is used to generate ATP from ADP in anaerobic conditions. A sprinters muscles often work so strenuously that the oxygen supply cannot meet the demand. The supply of ATP from mitochondria during aerobic respiration therefore stops. Sprinters with the most phosphocreatine have an advantage because ATP can be supplied to their muscles for longer so they can perform better.

Question 60

Dead dells can no longer produce ATP. Soon after death, muscles contract , making the body stiff- rigor mortis. From your knowledge of muscle contraction explain the reasons why rigor mortis occurs after death.

Answer 60

One role of ATP in muscle contration is to attach to the myosin heads, therefore causing them to detach from the actin filament and making the muscle relax. As no APT is produced after death, there is none to attach to the myosin, which therefore remains attached to actin, leaving the muscle in a contracted state- rigor mortis