6. Organisms Respond to change in environment EQs Flashcards
Explain the effect of myelination on the rate of nerve impulse conduction. (2 marks)
- myelin insulates
- saltatory conduction
Give one reason why a speed would be an underestimate of
the speed of transmission of an impulse along a neurone. (1 mark)
diffusion across synapse
Damage to the myelin sheaths of neurones can lead to problems controlling the
contraction of muscles.
Suggest one reason why. (2 marks)
- action potentials travel more slowly
- so delay in muscle contraction
A myelinated axon conducts impulses faster than a non-myelinated axon.
Explain this difference. (3 marks)
1.(In myelinated) action potential only at node(s);
2.(In myelinated, nerve impulse) jumps from node to node in saltatory conduction
3.(In myelinated) action potential does not travel along entire length
Describe how calcium ions are involved in synaptic transmission. (2 marks)
- (Nerve impulse causes) Ca 2+ to enter presynaptic neurone/membrane;
- (Ca 2+ entry) causes fusion of vesicles with presynaptic membrane
It is important that a neurotransmitter such as serotonin is transported back out of synapses. Explain why. (2 marks)
- (If not removed) keeps binding (to receptors);
- Keeps causing action potentials
Sodium and potassium ions can only cross the axon membrane through proteins.
Explain why. (2 marks)
- can not pass through phospholipid bilayer;
- because water soluble
The scientists then compared the length of time that the control mice and the
trained mice could carry out prolonged exercise. The trained mice were able to
exercise for a longer time period than control mice.
Explain why. (3 marks)
- (More aerobic respiration) produces more ATP;
- Anaerobic respiration delayed;
- Less or no lactate;
Dopamine is a neurotransmitter released in some synapses in the brain. The transmission of dopamine is similar to that of acetylcholine.
Dopamine stimulates the production of nerve impulses in postsynaptic neurones.
Describe how. (3 marks)
- (Dopamine) diffuses across (synapse);
- Attaches to receptors on postsynaptic membrane;
- Stimulates entry of sodium ions and depolarisation/action potential;
GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA
causes negatively charged chloride ions to enter postsynaptic neurones.
Explain how this inhibits postsynaptic neurones. (3 marks)
- (Inside of postsynaptic) neurone becomes more
negative/hyperpolarisation - More sodium ions required (to reach threshold)
- For depolarisation/action potential;
Explain why the student removed the shoot tip from each seedling. (2 marks)
- Tip produces IAA;
- Affects concentration of IAA
Explain why the student added glucose solution to each Petri dish in IAA experiment (2 marks)
- For respiration;
- Provide ATP/energy (for growth);
Explain why the lids were kept on the Petri dishes in IAA experiment (2 marks)
- To prevent/reduce evaporation;
- (Which) alters concentration of (IAA) solution
Explain how a decrease in the concentration of calcium ions within muscle tissues
could cause a decrease in the force of muscle contraction. (3 marks)
- (Less/No) tropomyosin moved from binding site
- (Fewer/No) actinomyosin bridges formed;
- Myosin head does not move
Damage to the myelin sheath of neurones can cause muscular paralysis. Explain why (3 marks)
- (Nerve)
impulses pass
to other neurones - (Nerve) impulses slowed/stopped;
A scientist investigated the effect of inhibitors on neurones. She added a respiratory
inhibitor to a neurone. The resting potential of the neurone changed from –70 mV
to 0 mV.
Explain why (3 marks)
- No/less ATP produced;
- No/less active transport
OR
Sodium/potassium pump inhibited; - Electrochemical gradient not maintained, no net movement of ions
Suggest two reasons why the patients had ziconotide injected into their cerebrospinal
fluid rather than taking a pill containing the drug. (2 marks)
- Rapidly/quickly/directly reaches spinal cord;
- Too large to be absorbed
When the patients recorded the intensity of pain, suggest two reasons why it was
important to use a statistically valid scale. (2 marks)
- (Sensation of) pain is subjective
- To ensure that differences (in pain detection)
were (statistically) significant
OR
For (valid) comparison;
Describe the function of the SAN (1 mark)
acts as a pacemaker
Describe the function of the purkyne tissue (1 mark)
conducts electrical impulses through the ventricle walls
State three chemical stimuli that cause the heart rate to increase during exercise (3 marks)
- increased blood co2
- decreased blood o2
- low blood pH
How does removing the AVN manage a fast and irregular heartbeat? (2 marks)
- avn passes wave of electrical activity to bundle of his and purkyne tissue to make ventricles contract
- no avn means the fast, irregular impulses from the atria aren’t transmitted via the bundle of his and purkyne tissue to the ventricles so they can’t affect heart rate
Why do people need a pacemaker after having their AVN removed due to a fast and irregular heartbeat? (2 marks)
- no avn means ventricles can’t contract normally
- pacemaker needed to generate electrical impulses that cause the heart to beat normally
Suggest why a potential difference of -45 mV is significant for this postsynaptic membrane (1 mark)
threshold needed to be reached for an action potential to fire
Rigor Mortis is the stiffening of muscles in the body after death. It happens when ATP reserves are exhausted. Explain why a lack of ATP leads to muscles being unable to relax (3 marks)
- atp provides the energy to break the actin-myosin cross-bridges
- mysoin heads will remain attached to actin filaments
- actin cannot slide back to relaxed position so muscle stays contracted
Bepridil is a drug that blocks calcium ion channels. Describe and explain the effect this drug will have on muscle contraction (3 marks)
- muscles won’t contract
- becase calcium ions not released to tropomyosin continues to block the actin-myosin binding sites
- no actin-myosin cross-bridges can be formed
Describe the importance of multiple negative feedback mechanisms in homeostasis (2 marks)
- gives more control
- as you can actively increase or decrease a level so it returns to normal
Would you expect the concentration of glucose to be lower at proximal ct or collecting duct? (1 mark)
collecting duct because glucose is reabsorbed at PCT so by the time filtrate reaches collecting duct there will be less glucose remaining
The level of ADH in the blood rises during strenuous exercise. explain the cause of the increase in ADH (4 marks)
- more sweating so more water lost
- decreases w.p of blood
- detected by osmoreceptors in hypothalamus
- which stimulates posterior pituitary land to release more adh
Gerbils have longer loops of henle than mice. Suggest and explain how this helps gerbils to produce less urine than mice (4 marks)
- a longer descending limb means more water can be reabsorbed into the blood from the nephron in the descending limb
- a longer ascending limb means more ions a.t out into medulla
- low w.p in medulla
- more water moves out collecting duct into capillaries, giving a low volume of urine
Suggest two advantages to a plant of having roots that respond to gravity by growing in the direction of its force (2 marks)
- roots grow downwards into soil, anchoring the plant
- brings closer to water for photosynthesis
Explain why brightly coloured objects often appear grey in dim light (2 marks)
- only rod cells stimulated in low light
- rod cells cannot distinguish between different colours therefore object is only perceived in black and white
Would would happen to high blood pressure if parasympathetic nerve endings were cut? (2 marks)
- remain high as parasympathetic system unable to transmit nerve impulses to SA node
- which decreases heart rate so lowers blood pressure
Why does higher temp mean more IAA is taken up? (2 marks)
- more kinetic energy
- more diffusion
Suggest how differences in cuticles means lower surface of plant has more IAA uptake than upper side? (2 marks)
- thin cuticle on lower surface
- more diffusion
The scientist investigated leaves of pear trees. How may the results by different for other species? (1 mark)
Different species have different (qualified) properties; e.g. number of stomata
The membrane potential in the pacinian corpuscle was the same whether medium or heavy pressure was applied. Explain why (2 marks)
- Threshold has been reached;
- all or nothing principle;
MS is a disease in which parts of the myelin sheath surrounding neurons are destroyed. Explain how this results in slower responses to stimuli (2 marks)
- No saltatory conduction
- More depolarisation over length of membranes;
What does the cell body of a neuron contain to make proteins and neurotransmitters? (1 mark)
rough endoplasmic reticulum
List three ways in which a response to a hormone differs from a response to a nerve impulse (3 marks)
- slow vs. rapid
- widespread vs. localised
- long-lasting vs. short-lived
How many milliseconds in a second? (1 mark)
1000
Explain why ions can only be exchanged at nodes of ranvier? (2 marks)
- because remainder of the axon is covered by a myelin sheath
- that prevents ions being exchanged
Describe what happens to the size of an action potential as it moves along an axon (1 mark)
remains the same
Explain how the refractory period ensures that nerve impulses are kept separate from one another (2 mark)
- sodium voltage-gated channels are closed
- so no sodium ions can move inwards and no action potential is possible
Suggest two reasons why mammals do not need a large diameter to achieve rapid transmission of action potentials (2 marks)
- mammals have myelinated neurons - saltatory conduction
- high body temp - increase rate of diffusion of ions
Explain how a presynaptic neurone is adapted for the manufacture of a neurotransmitter (2 marks)
- many mitochondria
- large amounts of endoplasmic reticulum
Explain why we barely notice backround noise but respond to louder noises (5 marks)
background:
1. produces low-level frequency of action potentials
2. insufficient amount of neurotransmitter to exceed threshold
loud:
4. produces high-level frequency of action potentials
5. sufficient amount of neurotransmitter to exceed threshold
6. temporal summation
Suggest an advantage in responding to high-level stimuli but not to low-level ones (2 marks)
- high-level stimuli need a response because they are more likely to be dangerous
- reacting to low-level stimuli can overload the nervous system
Explain why hyper-polarisation reduces the likelihood of a new action potential being created (2 marks)
- more sodium ions must enter to trigger an action potential
- less likely to reach threshold level
Explain why the neural pathways of reflex arcs have very few synapses (2 marks)
- fewer the synapses, shorter the overall time taken to respond to a stimulus
- advantage where a rapid response is needed
Why is it important serotonin is transported back out of synapses (2 marks)
- (If not removed) keeps binding (to receptors);
- Keeps causing action
potentials (in postsynaptic
membrane);
Describe the role played by tropomyosin (2 marks)
- Moves out of the way when calcium ions bind;
- Allowing myosin to bind (to actin)/crossbridge
formation;
Describe the role played by myosin (2 marks)
- Head (of myosin) binds to actin and slides actin past;
- (Myosin) detaches from actin and moves further along (actin)
- This uses ATP;
Explain why there is a high glycogen content in fast muscle fibres (2 marks)
- (Glycogen broken down) gives (lots of) glucose for glycolysis
- Glycolysis only yields 2 ATP per glucose
Explain why there is a high number of capillaries in slow muscle fibres (2 marks)
- (Many capillaries) give high concentration of oxygen
- Good glucose supply with little glycogen present;
- Allows high rate of/more aerobic respiration
People with McArdle’s disease produce less ATP than healthy people. Suggest why they can’t maintain strong muscle contraction (3 marks)
(Idea ATP is needed for:)
1. Cross bridges between actin and myosin;
2. ‘Power stroke’ / movement of myosin heads / pulling of actin;
3. Detachment of myosin heads;
4. Myosin heads move back to original position
Why are mitochondria distributed close to the outside of a slow muscle fibre? (2 marks)
- Short distance for diffusion of oxygen
- Oxygen used by mitochondria
You could use an optical microscope and a slide of stained muscle tissue to find the diameter of one of the muscle fibres. Explain how (2 marks)
- Measure with graticule/eyepiece scale;
- Calibrate against something of known size:
A student found the mean diameter for the slow muscle fibres in a section. Give two precautions and reasons why that show should have taken when sampling the fibres (2 marks)
- Equivalent measurements taken at random to avoid bias
- Large number to be representative/minimise
effect of extremes/of anomalies;
Give a reason why the values for heat generation and heat loss are measured per gram of body mass (1 mark)
- allows accurate comparisons even though animals have different body masses
Reptiles frequently seek shade when environmental temp rises above 25 degrees. Explain why (3 marks)
- the metabolic heat generation of the reptile beomes more rapid and so they generate heat faster than they can lose it
- their enzymes could become denatured
- reptiles have no physiological means of cooling
Why would there be an increase in evaporative heat loss in a mammal (1 mark)
sweating or panting increases
Cutting the nerves connecting the heat loss centre to the skin would be less likely to cause death than if those between the thermoreceptors and the heat loss centre were cut. Suggest why (2 marks)
- heat loss centre may be connected to effectors other than the skin which could lower blood temp
- e.g. regions of the brain that control behaviour and so the individual might be able to reduce blood temp by sheltering from sun
What are the blood vessels blood would pass through to get from the skin to the brain? (2 marks)
- vena cava, pulmonary artery
- pulmonary vein, aorta
Suggest an explanantion for hy tiredness is a sympton of diabetes (2 marks)
- if blood glucose level drops too much, no respiration
- muscle and brain cells may be less active
Suggest what lifestyle advice you might give someone in order to help them avoid developing type 2 diabetes (2 marks)
- match you carb intake to the amount of exercise you do
- to avoid becoming overweight limit carb intake, increase exercise
Suggest what might happen to the blood glucose conc of diabetics if they have no food for 24 hours (1 mark)
decrease as it is respired by cells
Suggest a reason why the efferent arteriole is not called a venule (2 marks)
- efferent arteriole later divides into a second capillary bed which surrounds loop of henle
- these them combine to form venule
Suggest another way in which you could show that the afferent arteriole was not a venule (1 mark)
structure of walls. arterioles have ticker walls with more muscle tissue than venules
Name the structure in which most of the water is reabsorbed (1 mark)
PCT
Explain how ADH causes the collecting ducts to reabsorb more water (3 marks)
- binds to receptors on the cell-surface membrane of cells lining the collecting duct and activate phosphorylase
- activation of phosphorylase causes vesicles containing pieces of plasma membrane that have aquaporins to fuse with membrane
- this increases number of water channels
Use your knowledge of how water is reabsorbed in the collecting ducts to explain why diabetics have dehydration (2 marks)
- reabsorption depends on large w.p gradient between fluid in collecting duct and blood capillaries
- presence of glucose in the fluid in collecting duct reduces gradient and leads to more water being lost in urine leading to dehydration
Describe how hormones are different in the cells they affect (1 mark)
only affect cells with right receptor
The rats were not fed for at least 6 hours before their blood glucose concentration was measured. Explain why (1 mark)
Glucose/sugar in food would affect the results;
Why would gene therapy with insulin in rats be useful / not useful to humans? (6 marks)
useful:
1. avoids injections
2. longer lasting
3. less restriction on diet
4. less need to measure blood sugar
not useful:
5. rats are different to humans;
6. may have side effects on humans;
7. long(er) term effects (of treatment) not known
When a person is dehydrated the cell volume of an osmoreceptor decreases. Explain why (2 marks)
- Water potential of blood will decrease;
- Water moves from osmoreceptor into blood
by osmosis;
Give two factors which could affect concentration of creatine in blood (2 marks)
- exercise
- muscle/body mass
Suggest why the pattern of protein filaments would differ in two images (2 marks)
- myofibril is contracting in one image, relaxing in other
- movement of actin fibres between myosin fibres;
Suggest two reasons why the concentration of glucose decreased after 1 hour even though this man’s blood contained no insulin (2 marks)
- glucose is used in cell respiration
- converted to glycogen
Explain the advantage to injecting both types of long and short term insulin before breakfast (2 marks)
- fast acting insulin reduces blood glucose from breakfast;
- slow acting insulin reduces blood glucose from
other meals before the evening meal /
eliminates the need to inject at lunch;
The cobra is poisonous. The molecular structure of the cobra permanently prevents muscle contraction. Explain why (2 marks)
- toxin binds to/competes for / blocks the acetylcholine receptors;
- acetylcholine cannot depolarise the membrane /
the toxin does not cause depolarisation;
The insecticide DFP combines with the active site of the enzyme acetylcholinesterase. The muscles stay contracted until the insecticide is lost (2 marks)
- acetylcholinesterase is unable to breakdown acetylcholine;
- acetylcholine still available to depolarise the membrane / generate action potentials in the
membrane;
