5.2 Excretion as an example of homeostatic control

Question 1

Excretion

Answer 1

Removal of metabolic waste from the body.

Question 2

Why must excess waste products be removed?

Answer 2

If allowed to accumulate, may inhibit enzyme activity or become toxic.

Question 3

What are the three main excretory products?

Answer 3

• Carbon dioxide (from R)
• nitrogen-containing compounds such as urea (nitrogenous waste)
• other compounds, such as bile pigments found in the faeces.

Question 4

What are the four main excretory organs?

Answer 4

1. THE LUNGS

Carbon dioxide passed from cells of Ring tissues into bloodstream –> lungs where it diffuses into alveoli to be excreted as you breathe out.

2. THE LIVER

Has many metabolic roles –> some substances produced will be passed into bile e.g. bilirubin. Also involved in deamination and Ornithine cycle (aa –> urea)

3. KIDNEYS

Urea (in solution-dissolved in plasma) passed into bloodstream to be transported to kidneys Kidney removes urea from blood –> urine –> stored in bladder before being excreted from body via urethra

4. SKIN

N.B Excretion not primary function

Sweat contains urea, uric acid and ammonia (all excretory products). Loss of water and salts may be an important part of H –> maintain body T and water potential of blood

Question 5

Importance of excretion

Answer 5

Allowing products of metabolism to build up could be fatal.

Carbon dioxide and ammonia are toxic–> interfere withe cell processes by altering the pH so normal metabolism is prevented.

Other metabolic products may act as inhibitors and reduce the activity of the essential enzymes.