osmoregulation

Question 1

The kangaroo rat is a small desert mammal. It takes in very little water in its food and it
rarely drinks. Its core body temperature is 38 °C.
The kangaroo rat takes in some water by feeding and drinking. Describe another method
by which the kangaroo rat could obtain water.

Answer 1

water from aerobic respiration

glucose +oxygen—-> co2 + WATER

Question 2

Describe how ultrafiltration produces glomerular filtrate.

Answer 2

1. Blood pressure / hydrostatic pressure;
2. Small molecules / named example;e.g water or urea or glucose
3. Pass through basement membrane / basement membrane acts as filter;
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries / presence of podocytes;

Question 3

Some people who have diabetes do not secrete insulin. Explain how a lack of
insulin affects reabsorption of glucose in the kidneys of a person who does not
secrete insulin.

Answer 3

1. High concentration of glucose in blood;
2. High concentration in tubule / in filtrate;
3. Reabsorbed by facilitated diffusion / active transport;
4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated;
6. Not all glucose is reabsorbed / some is lost in urine;

Question 4

A diabetic person and a non-diabetic person each ate the same amount of glucose.
One hour later, the glucose concentration in the blood of the diabetic person was
higher than that of the non-diabetic person. Explain why.

Answer 4

1. Lack of insulin / reduced sensitivity of cells to insulin;
2. Reduced uptake of glucose by cells / liver / muscles;
3. Reduced conversion of glucose to glycogen;

Question 5

The urine of a non-diabetic person does not contain glucose. Explain why.

Answer 5

(i) Leaves the blood at kidney;
glucose is reabsorbed at PCT

Question 6

If the glomerular filtrate of a diabetic person contains a high concentration of
glucose, he produces a larger volume of urine. Explain why.

Answer 6

Glucose in filtrate lowers water potential;
Lower Ψ gradient
Less water reabsorbed by osmosis;

Question 7

Explain how urea is concentrated in the filtrate.

Answer 7

Reabsorption of water / by osmosis;
descending LoH;

Question 8

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe
and explain how the secretion of ADH affects urine produced by the kidneys.

Answer 8

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.

Question 9

Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of
both men and women. Affected individuals have proteinuria (high quantities of
protein in their urine).
(a) Suggest how AS could cause proteinuria.

Answer 9

1. Affects/damages basement membrane
2. Proteins can pass into the (glomerular) filtrate/tubule;

Question 10

More than 99% of biological molecules are reabsorbed from the filtrate in
the proximal convoluted tubule.
Despite this, the concentration of fluid in this tubule remains constant.
Explain why.

Answer 10

water reabsorbed

Question 11

(b) Explain the shape of the curve in the loop of Henle in the graph.(graph looks like a triangle)

Answer 11

1. Concentration rises in descending limb because sodium ions enter and water lost;
   2.2. Concentration falls in ascending limb because sodium ions (and
   chloride) ions actively removed;
2. But water remains (in ascending limb) because its walls are
   impermeable (to water).

Question 12

What is the evidence in the graph that this person was secreting
antidiuretic hormone (ADH)?
Explain your answer.( there is an increase in the concentration gradient)

Answer 12

-water is reabsorbed by osmosis so higher concentration in collecting duct
- ADH increases permeability of collecting act to water

Question 13

(b) When a person is dehydrated, the cell volume of an osmoreceptor
decreases.
Explain why.

Answer 13

1. Water potential of blood will decrease;
   2.Water moves from osmoreceptor into blood by osmosis.

Question 14

Creatinine is a breakdown product of creatine found in muscle tissues.
Apart from age and gender, give two factors that could affect the
concentration of creatinine in the blood.

Answer 14

Sidney disease ethnicity