Summarize principles of Homeostasis

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M1.(a) 1. Release of glucagon; 2. Leads to formation of glucose in liver (cells);

Reject: glucagon breaks down glycogen, or any other biological molecule

3. From non-carbohydrates / amino acids / fatty acids. Accept: gluconeogenesis / references to glycogen as source of glucose

3

(b) 1. Mutant mice (mRNA suggests) make a lot of (the) enzyme; Accept: PCK1 made (for enzyme made)

2. Mutant mice use kidney / intestine (cells) to make glucose; Accept: use other organ (than liver)

3. Normal mice do this much less / normal mice use liver cells. 3

(c) 1. Differences significant; Reject: references to results being significant once

2. Probability of difference being due to chance less than 0.01 / 1% / 1 in 100 / probability of difference not being due to chance more than 0.99 / 99% / 99 in 100.

Ignore: references to 0.05 / 5% / 5 in 100 2

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M2.(a) 1. Positive correlation between sucrose and dopamine concentrations / higher concentration of sucrose, more dopamine;

Q NB question is ‘How do these ...’, not ‘Do these .... 1. Ignore simple statements of numbers from graph without description of trend

2. So (dopamine) makes them want to drink / eat more (sucrose);

3. Positive feedback because drinking / eating leads to wanting to drink / eat (even) more;

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3. It must be a clear statement of why this example is positive feedback, not inferred from points 1 and 2

3

(b) 1. (Refractory period) leads to discrete / separate nerve impulses / time when another nerve impulse can’t happen;

OR

(Refractory period) limits number of impulses per second / frequency of nerve impulses;

2. When maximum frequency reached / exceeded, no further increase in information / all (higher) concentrations of sucrose seem the same;

2

(c) 1. (Negative feedback) stops desire / wish to eat / appetite; 1. Accept stops dopamine release (in this context) 1. Accept makes them feel full

2. (This) limits amount eaten / stops eating; 2. Accept prevents constant eating

3. Prevents / reduces risk of obesity / too much energy intake; 3. Accept prevents vomiting Accept descriptions based on what would happen in absence of the feedback mechanism - or if stomach empty for points 1 and 2

3

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M3. (a) 1. (Acetylcholine) released from / in presynaptic side;

2. Receptors in postsynaptic (side) / binds on postsynaptic (side); 2. Mark for diffusion only awarded in context of unidirectional movement.

2

(b) (i) 1. Rapid response;

2. Short duration;

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Specific wording is not important. It is the principles that matter here. Points may be made by referring to figures.

2

(ii)

1 2 3

Percentage 80 0 0

Ignore % sign. 1

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M4. (a) (i) Eaten;

Containing carbohydrate / sugar;

Glucose absorbed from intestine / into blood;

Long time after insulin injection / needs more insulin / has not taken insulin;

Does not convert glucose to glycogen / glucose not taken up from blood; 2 max

(ii) Shows positive correlation / directly proportional;

A range of results for a particular value / values (for different colours) overlap;

Urine test only an arbitrary scale / not directly related to concentration / colour is subjective / few colour values;

Accept description 3

(b) Glycogen to glucose / glycogenolysis by activating enzymes; If name incorrect this disqualifies.

Gluconeogenesis; Allow explanation in terms of glucose from a

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non-carbohydrate / named non-carbohydrate source. 2

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M5.(a) (i) where a change triggers a response which reduces the effect of a change; 1

(ii) e.g. sweating, breathing, defaecating, other valid example; (reject respiration evaporation not acceptable as a 2nd mark if sweating or breathing given)

2 max

(iii) hypothalamus; 1

(b) (i) pituitary; (ignore anterior pituitary)

1

(ii) 1. ADH causes vesicles containing aquaporins / aquaporins to be inserted into membrane / collecting duct wall / plasma;

2. water enters cell through aquaporins; 3. by osmosis / diffusion / down a water potential gradient; 4. (from cell) to capillary; 5. via interstitial fluid;

4 max

(c) (i) excessive urination / drinking / diluted urine / thirst; 1

(ii) because males only have one X chromosome / do not have Y chromosome; a single copy of the recessive allele will be expressed;

2

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(iii) recessive alleles can be carried by individuals without showing effects / dominant allele always expressed; organism that are carriers more likely to reproduce / affected organism less likely to reproduce; therefore recessive alleles are more likely to be passed on / dominant alleles less likely to be passed on;

3

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M6. (a) (i) maintaining a constant internal environment; 1

(ii) one mark for example of factor kept constant; one mark for explaining its importance;

e.g. temperature / pH; optimum for enzymes / effect of pH / temperature on enzyme activity;

OR

water potential / blood glucose; effect of osmotic / blood glucose imbalance on cells;

2 max

(b) cannot interact with / move tropomyosin from binding sites on actin; (reject active sites) myosin(heads) do not bind / actinomyosin not formed; does not activate ATPase / energy not released from ATP;

3

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