homeostasis Q&A (2)

Question 1

What is homeostasis?

Answer 1

Maintaining a constant internal environment

Question 2

Describe the role of the hormone glucagon in the control of blood sugar concentration.

Answer 2

Binds to (specific) receptor; On muscle / liver cell;
Activation of enzymes (in liver);
Hydrolysis of glycogen;
(Facilitated) diffusion of glucose out of (liver cells) cells; Increases blood glucose levels

Question 3

Which hormone causes the decrease in the water content in the distal convoluted tubule?

Answer 3

ADH

Question 4

Explain the change in the amount of glucose.

Answer 4

reabsorption / passes back into blood; by active transport

Question 5

Explain the shape of the curve for sodium ions in the loop of Henle.

Answer 5

(sodium) ions pumped out of ascending limb;
water passes out of descending limb (into high concentration in tissue fluid / interstitial fluid);
some sodium ions re-enter descending loop (by diffusion);
high concentration at base of loop / some ions diffuse out near base increasing concentration outside loop

Question 6

Humans can produce urine which is more concentrated than their blood plasma.
(i) Explain the role of the loop of Henle in the absorption of water from the filtrate.

Answer 6

1. In the ascending limb sodium(ions) actively removed;
2. Ascending limb impermeable to water;
3. In descending limb sodium(ions) diffuse in;
4. Descending limb water moves out / permeable to water;
5. Low water potential / high concentration of ions in the medulla /
   tissue fluid;
6. The longer the loop / the deeper into medulla, the lower the water
7. Water leaves collecting duct / DCT;
8. By osmosis / down water potential gradient;

Question 7

Explain the role of ADH in the production of concentrated urine.

Answer 7

1. When water potential of the blood too low;
2. Detected by receptors in the hypothalamus;
3. Pituitary secretes / releases (more) ADH;
4. ADH increases the permeability / recruitment of aquaporins / opens channels for water in the DCT / collecting duct;
5. More water is reabsorbed / leaves the nephron moves into the blood;
6. By osmosis down the water potential gradient;

Question 8

Describe how excretion in this organ differs from excretion in a human nephron.

Answer 8

Ammonia not urea;
Ammonia (into labyrinth) enters by diffusion, not (ultra) filtration; Reabsorption of glucose from labyrinth, not PCT / no reabsorption in PCT;
All salt reabsorbed / no salt in urine, comparison to humans; Concentrated urine not produced

Question 9

Apart from water and glucose, name two substances which will be present in the glomerular filtrate.

Answer 9

urea
amino acids

Question 10

The glomerular filtration rate is the total volume of filtrate formed per minute. Explain the effect on the glomerular filtration rate of a large loss of blood from the body.

Answer 10

blood pressure decreased;
(less pressure) forms less filtrate;

Question 11

two ways in which the pct is adapted for reabsorption

Answer 11

microvilli provide large surface area;
carrier proteins (in membrane) for active transport; channel proteins for facilitated diffusion;
specific carriers for specific molecules / sodium pumps; (many) mitochondria for active transport

Question 12

A person with diabetes may have a plasma glucose concentration greater than the threshold value for glucose reabsorption. Explain what causes this raised plasma glucose concentration.

Answer 12

decrease in insulin production

Question 13

Salmonella typhimurium causes food poisoning in humans but not in other mammals. Explain why these bacteria attach to human cells but not to the cells of other mammals.

Answer 13

bacteria have ligands / antigens / proteins / glycoproteins / polysaccharides (on membrane / wall);
complementary to receptors / fits / binds / attaches to specific receptor

Question 14

Salmonella bacteria release toxins that cause the body temperature to rise. Although a small increase in body temperature can be beneficial, a large increase can cause serious harm.
Explain how a large increase in a person’s body temperature can cause harm.

Answer 14

enzymes denatured / tertiary / secondary structure altered / altered active sites / breaks hydrogen bonds;
prevents named chemical reactions / metabolic pathways

Question 15

Some species of bacteria, which live in soil and decompose organic material, release exotoxins. Suggest how the release of exotoxins benefits the bacteria.

Answer 15

kills other bacteria

Question 16

Washing hands with anti-bacterial soap reduces the risk of transmission of the bacteria that cause food poisoning. Tea tree oil is a plant extract used in soaps. It is claimed to have anti-bacterial properties. Outline a method for investigating this claim.

Answer 16

1prepare bacterial lawn
2 with oil and one with control / water / range of concentrations;
3 appropriate method of standardising how sample applied,
e.g. discs / wells;
4 appropriate measure of effectiveness / size / diameter of clear zone;
5 the larger the zone the greater the effectiveness;
6 use of aseptic technique

Question 17

Explain how the kidneys normally prevent glucose appearing in the urine of a non-diabetic person.

Answer 17

glucose reabsorbed / absorbed into blood; from proximal tubule by active transport

Question 18

The position and appearance of the lizard, as recorded by the infra-red camera, changed during the experiment. Describe and explain these changes.

Answer 18

moves to 40 °C side, then later to 20 °C;
gets lighter in hot side and darker in cool side; lighter as it absorbs heat / darker as it loses heat; by conduction / convection / radiation

Question 19

Suggest the advantage to the lizard of the behaviour shown.

Answer 19

lizard finds favourable environment;
(helps it to) maintain constant body temperature; advantage of this, e.g. for enzyme activity

Question 20

Explain how insulin lowers the concentration of blood glucose.

Answer 20

Binds to receptor on target/liver/muscle cell
Causes more transport/carrier proteins to become active/ move to (plasma) membrane
Glucose (diffuses) into cells (and lowers blood glucose)
(Enzymes in cells) convert glucose to glycogen; Stimulates fatty acids/lipid/fat formation (from glucose); Raises rate of respiration (in cells), using more glucose

Question 21

Describe how insulin reduces the concentration of glucose in the blood

Answer 21

insulin binds to specific receptors (on membranes);
insulin activates carrier proteins / opens channels / causes more
channels to form;
insulin increases the permeability of liver / muscle cells / tissues to glucose; insulin action results in glucose conversion to glycogen / glycogenesis;

Question 22

Explain the advantage of injecting both types of insulin before breakfast.

Answer 22

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

Question 23

One day, the man did not eat a midday meal. Suggest one reason why his blood glucose concentration did not fall dangerously low even though he had injected himself with the mixture of insulin before breakfast.

Answer 23

glucagon is still active;
glycogen converted to glucose / glycogenolysis

Question 24

Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct.

Answer 24

(epithelial cell) of tubule cells carry out active transport; transport chloride / sodium ions out (of filtrate);
against concentration gradient;
into surrounding tissue / tissue fluid;
creates / maintains water potential gradient for water reabsorption; countercurrent multiplier

Question 25

Explain how ADH is involved in the control of the volume of urine produced.

Answer 25

if water potential of blood falls, detected by receptors in hypothalamus; leads to ADH released from pituitary gland;
ADH makes cells of collecting duct / distal convoluted tubule permeable to water
water leaves filtrate by osmosis; smaller volume of urine produced