Form 2:
Excretion and Homeostasis kcse questions

Home|Table of content

1. In an investigation the pancreatic duct of a mammal was blocked. It was found that the blood sugar regulation remained normal while food digestion was impaired. Explain these observations. ( 2 marks)

Pancreatic juice containing digestive enzyme is prevented from reaching food. Insulin (and glucagons), which regulates sugar, is released directly into the blood stream.

2. (a) Explain why the body temperature of a healthy human being must rise up to 390c on a humid day. (2 marks)

Heat from the body metabolism is not lost to the surrounding through sweating because evaporation of sweat will be low; as air is already saturated with moisture.

(b) In an experiment a piece of brain was removed from rat. It was found that the rat had large fluctuations of body temperatures suggest the part of the brain that had been removed. ( 1 mark)

Hypothalamus

3. (a) Explain why sweat accumulates on a person’s skin in a hot humid Environment. (2 marks)

Sweat produced does not evaporate due to high humidity and the body does not cool, hence more sweat produces leading to accumulation

(b) Name the specific part of the brain that triggers sweating. ( 1 marks)

Hypothalamus

4. Explain why some desert animals excrete uric acid rather than ammonia. (2 marks)

-Elimination of uric acid requires less water than ammonia, hence (more) water is conserved.

- Uric acid is less toxic than ammonia hence safer to excrete where there is less water

5. State the role of the following hormones in the body

(a) Insulin (3 marks)

Regulation of blood sugar lowers blood sugar level/controls the conversion of blood sugar to glycogen/maintain correct blood sugar level (90-100mg/100cc of blood)

(b) Antidiuretic Hormone (3 marks)

Controls the absorption of water in the kidney (tubules) nephron/regulation of water in the body/osmotic pressure in the blood.

6. What osmoregulatory changes would take place in a marine amoeba if it was transferred to a fresh water environment?

More water will enter the amoeba (by osmosis) rate of water discharge by contractile vacuole will increase. Contractile vacuoles will be formed to discharge the excess water.

7. Name two components of blood that are not present in glomerular filtrate. ( 2 marks)

i) Proteins/plasma; protein/fibrinogen; albumin, globulin, prothrombin. ii) Blood cells, RBC/white blood cells/Platelets.

8. How would one find out from a sample of urine whether a person is suffering from diabetes mellitus? (2 marks)

- Tests/React/Boil urine with Benedicts/Fehlings: positive results/Orange red precipitate is an indication of the disease diabetes mellitus. - Brick red instead of orange, use of Benedict’s solution with boiling/heating.

9. When is glycogen, which is stored in the liver, converted into glucose and released into the blood? ( 2 marks)

After vigorous activity when blood glucose falls below normal.

10. A person was found to pass out large volumes of dilute urine frequently. Name the

(a) Diseases the person was suffering from (1 marks)

Diabetes insipidus

(b) Hormone that was deficient (1 mark)

Anti-diuretic Hormone/ADH/ vasopressin

11. State the importance of osmoregulation in organisms ( 2 marks)

Maintenance of constant level of water, salts, osmotic pressure for optimum conditions for metabolism, suitable condition for cellular functions.

12. What happens to excess fatty acids and glycerol in the body? (2 marks)

Converted into fats and stored as adipose tissue.

13. Give reasons for each of the following

(a) Constant body temperature is maintained in mammals ( 1 mark)

a) - Most enzymes in the body function with a narrow range of temperature - High temperature denatures enzymes - Low temperature inactivates/inhibit enzymes

(b) Low blood sugar level is harmful to the body ( 2 marks)

Sugar is a raw material for respiration therefore less sugar leads to low rate of respiration hence less energy available to the body/low rate of metabolism.

14. The temperature of a person taken before during and after taking a cold bath. The results are shown in the graph

(a) Explain why the temperature fell during the bath ( 2 marks)

Heat loss by conduction/convection from the blood vessels, the skin enters general circulation cooling the body.

(b) What changes appeared in the skin that enabled the body temperature to return to normal. (2 marks)

Vasoconstriction, thus less blood flowing to the skin surface thus reducing heat loss. Sweating ceases. Heat produced by shivering through metabolism is retained in the body

15. (a) Name the fluid that is produced by sebaceous glands (1 mark)

Sebum

16. What is the role of sweat on the human skin? ( 2 marks)

- Cooling the body when water content evaporates.

- Excrete excess salts, lactic acid and urea.

17. Describe how the human kidney functions. ( 20 marks)

(check out the essays section-form 2 essays)

18. (a) What is the meaning of the following terms:

(i) Homeostasis ( 1 mark)

Maintenance of a constant internal environment of cells.

(ii) Osmoregulation ( 1 mark)

Regulation of the concentration of water and salts in the body fluid

19. (a) Explain what happens to excess amino acids in the liver of humans.  ( 3 marks)

- The amino acids are broken into amino group (NH2) and carboxyl group 149 (COOH). The amino group combines with hydrogen forming highly toxic ammonia. It immediately carbines with carbon (IV) oxide forming urea that is less toxic.

- The carboxyl group are converted to carbohydrates and then oxidized or converted into neutral fats and deposited on parts of the human.

(b) Which portions of the human nephrons are only found in the cortex?(3 marks)

- Bowman’s capsule

- Proximal convoluted tubule

- Distal convoluted tubule

(c) (i) What would happen if a person produced less antidiuretic hormone?  ( 1 mark)

Less water reabsorbed in the blood stream and dilute urine is produced.

(ii) What term is given to the condition described in (c) (i) above?  ( 1 mark)

Diabetes insipidus

20. Define the following terms ( 3 marks)

(a) Excretion

Excretion is the removal of metabolic waste products from the body of an organism

(b) Secretion

Secretion is the removal of a substance from a cell where it is formed and its transfer to another part of the body where it serves a useful function

(c) Egestion

Egestion is the removal of undigested food material from the body of an organism

 21. Name the components of blood that do not enter the renal tubule in mammals  (2 marks)

Blood cells and plasma proteins

22. The table below shows the approximate percent concentration of various components in blood plasma entering the kidney glomerular filtrate and urine of a healthy human being.

(b) Name the process responsible for the formation of glomerular filtrate.

Ultra filtration

(c) What process is responsible for the absence of glucose and amino acids in urine?

Ultra filtration

(d) Explain why there are no plasma proteins in the glomerular filtrate

Because the pores in the glomerular capillaries are too small for plasma protein to pass through.

(e) Besides plasma proteins what other major component of blood is absent in the glomerular filtrate.

Blood cells

(f) Why is the concentration of urea in urine much higher than its concentration in the glomerular filtrate?

Most of the water in the glomerular filtrate is reabsorbed by the urine is formed whereas very little urea is reabsorbed.

23. When the environmental temperature is very high, some animals urinate on their legs or lick the sides of their body. How does this help in temperature regulation?

As moisture from the urine or saliva evaporates from the surface of the skin, it reabsorbs latent heat of vaporization from the body thus cooling it

24. Fish are able to use more of their food intake for growth than mammals. Suggest an explanation for this.

Being exothermic, fish do not spend any part of their food intake in the maintenance of body temperature. This is unlike the case with mammals which spend a significant part of their food on temperature maintenance. Therefore fish are able to spend more of their food intake on growth.

25. Explain the term negative feedback

Negative feedback refers to a regulatory mechanism whereby a deviation of the entity being regulated above or below the normal range triggers a sequence of event to bring it back to normal.

26. Study the diagram below and answer the questions that follow.

(a) Name the blood vessels labeled A, B and C.

A - Hepatic artery

B - Hepatic portal vein

C - Hepatic vein

(b) If the animals has recently fed on a diet which is rich in proteins and carbohydrates in which of the vessels labeled A, B, and C would you expect to find the highest concentration of:

(i) Glucose -B

(ii) Amino acids- B

(iii) Carbon (IV) oxide-C

(iv) Oxygen- A

(v) Urea- C

(c) During fasting, the level of blood glucose in vessels C may be higher than the level in vessel B explain

During fasting there is no glucose from the alimentary canal making glucose concentration in vessel B low. Vessel C obtains glucose derived from the hydrolysis of glycogen in the liver.