EXCRETION AND HOMEOSTASIS - KCSE BIOLOGY NOTES

​SPECIFIC OBJECTIVES

By the end of the topic, the learner should be able to:

1. distinguish between excretion and egestion
2. explain the necessity for excretion in plants and animals
3. state the uses of excretory products of plants
4. describe the methods of excretion in a named unicellular organism
5. relate the structures of the human skin, lungs, liver and kidney to their functions name common kidney diseases
6. explain the concept of internal environment and homeostasis
7. compare responses to changes in temperature by behavioural and physiological methods in animals
8. relate heat loss to body size in
9. describe methods by which mammals gain and lose heat
10. explain how the functions of the following relate to homeostasis - skin, hypothalamus, liver and kidney
11. discuss the role of antidiuretic hormone, insulin and glucagons
12. describe simple symptoms of Diabetes mellitus and Diabetes insipidus.

​TOPICS / SUB-TOPICS OUTLINE

Excretion in Plants
Methods of excretion in plants

• Useful and harmful excretory products of plants and their economic importance e.g. caffeine in tea and coffee, quinine, tannins, colchicines, cocaine, rubber, gum, papain (from pawpaw) and products of cannabis sativa (bhang) and khat (miraa)Excretion and homeostasis in Animals

Distinction between excretion, homeostasis and egestion
Excretion in a named uni-cellular organism (protozoa)
Structure and functions of skin and kidney
Neuro-endocrine system and homeostasis

• Water balance (blood osmotic pressure)
• Blood sugar level (control)
• Temperature regulation (mention the role of hypothalamus)

Common kidney diseases, their symptoms and possible methods of prevention and control
The role of the skin in thermoregulation, salt and water balance.
Major functions of the liver and their contributions to homeostasis.
Common diseases of the liver, their symptoms and possible methods of prevention and control
Practical Activities
Examine and draw the mammalian kidney
Make vertical sections of the kidney to identify cortex and medulla
Observe permanent slides of mammalian skin
Investigate effect of catalase enzyme on hydrogen peroxide

Introduction ​Excretion and Homeostasis 

• Excretion is the process by which living organisms separate and eliminate waste products of metabolism from body cells.
• If these substances were left to accumulate, they would be toxic to the cells.
• Egestion is the removal of undigested materials from the alimentary canals of animals.
• Secretion is the production and release of certain useful substances such as hormones, sebum and mucus produced by glandular cells.
• Homeostasis is a self-adjusting  mechanism to maintain a steady state in the internal environment

Excretion in Plants 

• Plants have little accumulation of toxic waste especially nitrogenous wastes.
• This is because they synthesise proteins according to their requirements.
• In carbohydrate metabolism plants use carbon (IV) oxide released from respiration in photosynthesis while oxygen released from photosynthesis is used in respiration.
• Gases are removed from the plant by diffusion through stomata and lenticels.
• Certain organic products are stored in plant organs such as leaves, flowers, fruits and bark and are removed when these organs are shed.
• The products include tannins, resins, latex and oxalic acid crystals.
• Some of these substances are used illegally.
• Khat, cocaine and cannabis are used without a doctor's prescription and can be addictive.
• Use of these substances should be avoided.

EXCRETION AND HOMEOSTASIS QUESTIONS AND ANSWERS

1. Define the following terms
   1. Excretion
   2. Secretion
   3. Egestion
   4. Homeostasis
2. Explain why excretion is necessary in plants and animals
3. Describe how excretion takes place in green plants
4. Why do plants lack complex excretory structures like those of animals?
5. State the excretory products of plants and some of their uses to humans
6. Describe excretion in unicellular organisms
7. Draw and label a mammalian skin
8. Explain how the mammalian skin is adapted to its functions
9. What is the role of lungs in excretion?
10. State the functions of the liver
11. Draw a labeled diagram of mammalian nephrone
12. Describe how the human kidney functions
13. State the adaptations of proximal convoluted tubule to its function
14. Name the common kidney diseases
15. Why is homeostatic control necessary?
16. What is internal environment?
17. Why is constant body temperature maintained by mammals?
18. Explain the advantage gained by possessing a constant body temperature
19. How do mammals regulate body temperature?
20. Why does body temperature of a healthy person rise up to 37oC on a hot humid day?
21. Name the structures in the human body that detect external temperature changes 
22. State the advantages that organisms with small surface area to volume ratio experience over those with larger
23. Explain why individuals with smaller sizes require more energy per unit body weight than those with larger sizes.
24. What is the meaning of osmoregulation?
25. State the importance of osmoregulation
26. State the ways by which desert mammals conserve water
27. Explain why some desert animals excrete uric acid rather than water
28. Explain why eating a meal with too much salt leads to production of a small volume of concentrated urine
29. Explain how marine fish regulate their osmotic pressure
30. What is the biological significance of maintaining a relatively constant sugar level in a human body?
31. Discuss the role of the following hormones in blood sugar control Insulin
32. Explain the part played by antidiuretic hormone in homeostasis
33. What is the role of blood clotting in homeostasis?
34. Describe the role of the following hormones in homeostasis
35. Distinguish between diabetes mellitus and diabetes insipidus
36. How can high blood sugar level in a person be controlled?
37. Why does glucose not normally appear in urine even though it is filtered in the mammalian Bowman’s capsule?
38. When is glycogen which is stored in the liver converted into glucose and released into the blood?
39. How would one find out from a sample of urine whether a person is suffering from diabetes mellitus?

ANSWERS

KCSE KNEC QUESTIONS

ANSWERS

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