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AQA A2 Biology B16 Homeostasis Kerboodle Answers

This page contains the AQA A2 Biology B16 Hpmeostasis Questions and kerboodle answers for revision and understanding.This page also contains the link to the notes and video for the revision of this topic.
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C16.1 Principles of homeostasis AQA A2 Biology B16 Homesostasis Kerboodle Answers: Page No. 116

1 Homeostasis is the maintenance of a constant internal environment in organisms. 2 Maintaining a constant temperature is important because enzymes function within a narrow range of temperatures. Fluctuations from the optimum temperature mean enzymes function less efficiently. If the variation is extreme, the enzyme may be denatured and cease to function altogether. A constant temperature means that reactions occur at a predictable and constant rate. 3 Maintaining a constant blood glucose concentration is important in ensuring a constant water potential. Changes to the water potential of the blood and tissue fluids may cause cells to shrink and expand (even to bursting point), due to water leaving or entering by osmosis. In both instances the cells cannot operate normally. A constant blood glucose concentration also ensures a reliable source of glucose for respiration by cells.

16.2 Feedback mechanisms AQA A2 Biology B16 Homesostasis Kerboodle Answers : Page No. 120

1 If the information is not fed back once an effector has corrected any deviation and returned the system to the set point, the receptor will continue to stimulate the effector and an over-correction will lead to a deviation in the opposite direction from the original one. 2 It gives a greater degree of homeostatic control.

16.4 Diabetes and its control AQA A2 Biology B16 Homesostasis Kerboodle Answers : Page No. 128

1 Type I is caused by an inability to produce insulin. Type ll is caused by receptors on body cells losing their responsiveness to insulin. 2 Type I is controlled by the injection of insulin. Type II is controlled by regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken. 3 Diabetes is a condition in which insulin is not produced by the pancreas. This leads to fluctuations in the blood glucose level. If the level is below normal, there may be insufficient glucose [or the release of energy by cells during respiration. Muscle and brain cells in particular may therefore be less active, leading to tiredness. 4 Match your carbohydrate intake to the amount of exercise that you take. Avoid becoming overweight by not consuming excessive quantities of carbohydrate and by taking regular exercise.

16.5 Control of blood water potential- structure of the nephron AQA A2 Biology B16 Homesostasis Kerboodle Answers : Page No. 133

The nephron is the structural unit of the kidney. It comprises a cup-shaped structure called the renal (Bowman’s) capsule (1) that contains a knot of blood vessels called the glomerulus (2) which receives its blood from a vessel called the afferent (3) arteriole. The inner wall of this cup-shaped structure is lined with specialised cells called podocytes (4) and from it extends the first, or proximal (5), convoluted tubule whose walls are lined with epithelial cells (6) that have microvilli (7) to increase their surface area. The next region of the nephron is a hairpin loop called the loop or Henle (8) which then leads onto the second, or distal (9), convoluted tubule. This in turn leads onto the collecting duct (10) which empties into the renal pelvis. Around much of the nephron is a dense network of blood vessels called the glomerulus (11) capillaries.

16.6 Role of the nephron in osmoregulation AQA A2 Biology B16 Homesostasis Kerboodle Answers : Page No. 139

1 Proximal convoluted tubule 2 Glomerulus; renal capsule; proximal convoluted tubule; loop of Henle; distal convoluted tubule; collecting duct
Microvilli to provide a large surface area to reabsorb substances from the filtrate; infoldings at their bases to give a large surface area to transfer reabsorbed substances into blood capillaries; a high density of mitochondria to provide ATP for the active transport. 4 Animals in dry environments would have longer loops of Henle 10 give a longer counter current multiplier and so more absorption of water by the collecting duct.

16.7 The role of hormones in osmoregulation AQA A2 Biology B16 Homesostasis Kerboodle Answers : Page No. 142

1 Hypothalamuss 2 a Less-because the water drunk causes a rise in water potential of the blood bMore-because intense exercise leads LO sweating and the loss of water leading to a fall in water potential of the blood 3 ADH binds to receptors on the cell-surface membrane of the cells lining the collecting duct and activate phosphorylase within the cell. The activation of phosphorylase causes vesicles containing pieces of plasma membrane that have numerous water channels/aquaporins to fuse with the cell-surface membrane. This increases the number of water channels and makes the cell surface membrane much more permeable to water. 4 0.05 g dm-1 Banner 3

Practice questions: Chapter 16: Page No. 143-145

1 (a)
  1. Positive correlation between sucrose and dopamine concentrations/higher concentration of sucrose, more dopamine.
  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.
(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.
  1. When maximum frequency reached/exceeded, no further increase in information/all (higher) concentrations of sucrose seem the same.
(c
  1. (Negative feedback) stops desire/wish to eat/appetite.
  2. (This) limits amount eaten/stops eating.
  3. Prevents/reduces risk of obesity/too much energy intake.
2 (a) (i) Hormones have widespread effect / affect different organs / affect different parts of the body / affect distant organs / only affect cells with right receptor. (ii)
  1. Hormones in blood.
  2. Local chemical mediators spread by diffusion / spread directly.
(b)
  1. (Acetylcholine) released from/in presynaptic side.
  2. Diffusion from higher concentration/to lower concentration.
  3. Receptors in postsynaptic (side) / binds on postsynaptic (side).
(c) (i)
  1. Rapid response.
  2. Short duration.
(ii) 3 (a) 1. Adenylate cyclase activated / cAMP produced / second messenger produced.
  1. Activates enzyme(s) (in cell).
  2. (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited.
(b) Scientists made an artificial gene which codes for insulin. They put the gene into a virus which was then injected into rats with type I diabetes. The virus was harmless to the rats but carried the gene into the cells of the rats. The treated rats produced insulin for up to 8 months and showed no side-effects. The scientists measured the blood glucose concentrations of the rats at regular intervals. While the rats were producing the insulin, their blood glucose concentrations were normal. (i)
  1. Glucose/sugar in food would affect the results.
  2. Food/eating would affect blood glucose (level).
  3. (Allows time for) blood glucose (level) to return to normal.
(ii) Type 2 diabetes is a failure to respond to insulin / still produces insulin / is not insulin-dependent. (iii) Research workers have suggested that treating diabetes in humans by this method of gene therapy would be better than injecting insulin. Evaluate this suggestion. (4 marks) AQA June 2012 For:
  1. Avoids injections / pain of injections;
  2. Long(er) lasting / permanent / (new) cells will contain/ express gene;
  3. Less need to measure blood sugar / avoids the highs and lows in blood sugar;
  4. Less restriction on diet;
Against:
  1. Rats are different to humans.
  2. May have side effects on humans.
  3. Long(er) term effects (of treatment) not known / may have caused effects after 8 months.
  4. (Substitute) insulin may be rejected by the body.
4 (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. (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. (b) Glycogen to glucose/glycogenolysis. By activating enzymes. Gluconeogenesis. 5 (a) Hypothalamus. (b)
  1. Water potential of blood will decrease.
  2. Water moves from osmoreceptor into blood by osmosis.
(c)
  1. Permeability of membrane/cells (to water) is increased.
  2. More water absorbed from/leaves distal tubule/collecting duct.
  3. Smaller volume of urine.
  4. Urine becomes more concentrated.
(d) 115.2/115.3 (cm3 minute-1) (e) Muscle/body mass Ethnicity Exercise Kidney disease – do not accept ‘health’ 6 (a) 10cm3 10 m Mol dm-3 glucose + 90cm3 water = 1 10 m Mol dm-3 glucose. 10cm3 1 m Mol dm-3 glucose + 90cm3 water = 0.1 10 m Mol dm-3 glucose. 10cm3 0.1m Mol dm-3 glucose + 90cm3 water = 0.01 10 m Mol dm-3 glucose. 10cm3 0.01 m Mol dm-3 glucose + 90cm3 water = 0.001 10 m Mol dm-3 glucose. (b) (c) Log scale allows very large differences in values to be accommodated on a short scale. (d) Will be around 0.18m Mol dm-3 glucose. Banner 4

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