This was the more popular question in this section and candidates who attempted it
performed fairly well.
Most candidates could state three ways in which water is of importance to mammals e.g.
temperature regulation e.t.c. but some candidates wrote domestic uses of water and lost
marks.
Candidates could properly name structures that excrete water in mammals and plants
and name four plant hormones but lost some marks due to spelling errors.
In describing how the mammalian body responds to low water content a lot of candidates
performed poorly and scored low marks.
Expected answers include:
Response to low water content in the mammalian body
- the hypothalamus will detect low water high/osmotic pressure in the blood;
- nervous impulses will be sent to the posterior pituitary gland; to release antidiuretic
hormone/ADH into the blood;
- the ADH increases the permeability of the kidney tubules to water;
- more water will be reabsorbed from the kidney tubules into the blood capillaries; the
blood’s osmotic pressure will be reduced;
- little amounts of urine/ concentrated urine/hypertonic urine is produced;
- as hypertonic urine is produced; more water will be absorbed from the colon/ rectum
into the blood;
- the skin will also reduce the production of sweat in order to conserve water.
