Homeostasis in Animals

TEACHERS’ GUIDE

SUBJECT : BIOLOGY

UNIT : 1

TOPIC : Excretion and Homeostasis

SUB-TOPIC : Excretion in animals

CLASS : Senior 3

CLASS SIZE : 60 Students

TIME REQUIRED : Minimum: 120 – 160 minutes (i.e. 3-4 periods)

Brief description of Unit

Animals excrete water, excess salts, and nitrogenous wastes through the urinary system. The main nitrogenous waste excreted by animals is urea, although there are traces of uric acid and ammonia in their urine.

In this unit learners will be introduced to the structure of the urinary system. In addition they will learn about the role of the urinary system in removing waste products from the body; and the fact that some wastes are “wealth” or useful. They will also appreciate the need for proper disposal of waste (i.e. dangerous if poorly disposed; e.g. spreading diseases; advantageous if properly disposed, e.g. enriching crop yields).

Content and concepts to emphasise

• Components of the urinary system (kidneys, bladder, urethra, ureters)
• The structure and function of a mammalian kidney

Objectives

By the end of the unit the learners should be able to;

1. Draw and label the parts of the urinary system
2. Locate the position of the kidneys in a mammal
3. Describe the structure of mammalian kidneys
4. Describe the nephron as the functional unit of kidney
5. Explain how kidneys function in getting rid of waste products from the body
6. Describe how urine and other organic wastes can be used to improve crop yields
7. Describe the proper disposal of urine
8. State effects of poor disposal of wastes

Materials required

1. A Chart showing;

1. The urinary system
2. The gross structure of the kidney
3. The nephron

2. A Dissected small mammal (rabbit or rat) to show the urinary system.

3. Photographs / stories of activities in which the urine of humans and domestic animals is used as a fertiliser.

4. A Chart / story about diseases or any other effects of poor urine disposal.

Job related life skills

1. Personal attributes – self confidence, time management, creativity/imaginative, recording skills

2. Communication – observation and listening skills,

3. Team work – task- oriented, leadership skills

4. Problem solving - information seeking, environmental protection and conservation

5. Application of number - numeracy (as they compare crop yields in treated and untreated plots)

Learners’ Activities

Activity One

Ask learners to observe a chart to identify parts of the urinary system (kidneys, ureters, the bladder and urethra).

Ask learners to discuss parts of the urinary system and draw a labelled diagram.

Activity Two

Ask learners to observe a dissected rat / rabbit to identify the parts of the urinary system.

Activity Three

Project/field activity A 1. In groups of 4-6 ask the learners to find out:

1. If urine (for humans or domestic animals) is put to proper use in their community.
2. How urine and other organic wastes are used and the processes (steps) of putting it to use.

2. Let them record their findings on a flip chart or manila card

3. Accord each group some time to give feedback to the plenary

4.Let the class discuss the presentations of each group and the advantages of using urine and other organic wastes.

5. Display results on a notice board

6. Encourage learners to practice what they have learnt.

Activity Four

Project/field activity B

In groups of 4-6 ask the learners to prepare two small gardens at school and plant some crops. They should then prepare fertilisers from urine and apply it to one of the gardens.

Ask them to compare the yields of the gardens treated with urine fertilisers with those from untreated gardens.

Encourage the learners to practise what they have learnt and always try to monitor their projects.

Activity Five

Preparation of fertilisers from Urine

Procedure

1. Collect urine in a jerrycan, bucket or any other suitable container.
2. Allow it to ferment for two weeks.
3. Dilute it with water in a ratio of 1:4 (urine to water)
4. You can enrich this fertiliser (which is rich in nitrates) further by adding ash to provide other nutrients such as potassium.
5. You can add hot pepper or chilli to the fertiliser to kill pests, which may destroy plants.

To ensure that your learners have understood you can ask them to do the following exercises in order to con concretise the content.

Exercise

Section A

Multiple Choice questions

Select the best answer for each question

1. Urine is formed in the…………………..

A. bladder

B. kidney

C. ureter

D. urethra

2. The functional unit of a kidney is called a………………………

A. cortex

B. medulla

C. nephron

D. nephridium

3. Which of the following wastes is eliminated by the kidney?

A. carbon dioxide

B. salts

C. water

D. ammonia

4. The blood vessel that supplies blood to the kidney is the…………………

A. aorta

B. renal vein

C. water

D. hepatic artery

5. The outer most part of the kidney is called the…………………..

A. medulla

B. cortex

C. pyramid

D. pelvis

6. The main nitrogenous metabolic waste product eliminated by the kidney is………

A. water

B. carbon dioxide

C. urea

D. uric acid

7. What part of the urinary system stores urine?

A. kidney

B. bladder

C. ureter

D. urethra

8. On which part of the nephron is most of the water reabsorbed?

A. distal convoluted tubule

B. loop of Henle

C. proximal convoluted tubule

D. Bowman’s capsule

Section B

Structured questions

Study the diagram below and answer the questions that follow

1. Label the parts marked A – E.

A ……………………………………

B ……………………………………

D ……………………………………

E ……………………………………

2. State the functions of the following parts

A ………………………………………………………………………………………………………………………………………

B ……………………………………………………………………………………………………………………………………….

D ………………………………………………………………………………………………………………………………………

E ………………………………………………………………………………………………………………………………………

3. Blood vessel X is wider than vessel Y. What is the importance of this difference?

Section C Essay questions

1. (a) Define the term excretion.

(b) How is urine formed?

(c) (i) What problems may arise from improper disposal of urine?

(ii) In what ways is urine a useful waste?

Answers

Section A

1. B 2. C 3. A 4. C

5. B 6. C 7. B 8. C

Section B

1. A. Bowman’s capsule

B Proximal convoluted tubule

C Loop of Henle

D Distal convoluted tubule

E Collecting tubule / duct

2. (i) A ultra filtration

(ii) B selective re-absorption of glucose, amino acids, some water, salts

(iii) D re-absorption of water

(iv) E re-absorption of water

3. To develop hydrostat pressure which brings about ultra filtration.

Section C

1. (a) Excretion is the process by which waste products of metabolism are removed from living cells / tissues.

(b) Urine is formed through ultra filtration followed by selective re-absorption. Hydrostatic pressure develops in the glomerulus because the efferent vessel is narrower than the afferent vessel. Ultra filtration / pressure filtration occurs, forcing glamerular filtrate into the capsular space. The filtrate consists mainly of water, amino acids, glucose, salts and urea. Selective re-absorption occurs at the proximal and distal convoluted tubules. Most of the water, all glucose, all amino acids and some salts are reabsorbed into the blood stream. The excess water, and excess salts constitute urine.

(c) (i) - Spreading of diseases e.g. Bilharzia, candidiasis

- Pollution of the environment

(ii) - Can be used to make biogas

- Can be used to make (organic) fertilizers.