AQA GCSE Biology: Homeostasis and Response

On a hot day a person sweats a great deal and does not drink much water, so the water content of their blood falls (the blood becomes too concentrated). The body responds using the hormone ADH and the kidneys to restore the normal water level.

Describe and explain how the body responds to bring the water content of the blood back to normal. (6 marks)

A doctor tested the urine of four people for glucose. In a healthy person, all the glucose filtered by the kidneys is reabsorbed back into the blood, so none appears in the urine.

Person	Blood glucose / mg per 100 cm³	Glucose in urine?
A	90	No
B	95	No
C	320	Yes
D	110	No

(a) A normal blood glucose level is about 90 mg per 100 cm³. Calculate how many times greater Person C's blood glucose is than Person A's. (2 marks)

(b) Person C has glucose in their urine. Suggest what this result indicates about Person C, and explain why glucose appears in their urine. (2 marks)

The eye can change the shape of its lens to focus light from objects at different distances. This is called accommodation.

Describe what happens to the ciliary muscles, the suspensory ligaments and the lens when the eye focuses on a near object. (3 marks)

Blood glucose concentration is controlled by hormones from the pancreas.

(a) Name the hormone released by the pancreas when blood glucose concentration is too high. (1 mark)

(b) Describe how this hormone causes the blood glucose concentration to fall. (2 marks)

When a plant shoot is lit from one side only, it grows so that it bends towards the light. This response is called phototropism and is controlled by the plant hormone auxin.

Explain, in terms of auxin, why the shoot bends towards the light. (2 marks)

In a reflex action, a nerve impulse travels along a reflex arc. The impulse passes from a sensory neurone to a motor neurone across a small gap.

Name the small gap between two neurones where the impulse is passed from one neurone to the next. (1 mark)