AQA GCSE Biology: Homeostasis and response 6-mark questions

The rise in body temperature is detected by temperature receptors, which send information to a coordination centre in the brain. The brain sends signals to effectors such as sweat glands and muscles in the walls of skin arterioles. Sweat glands produce more sweat, which cools the body as it evaporates, and the arterioles widen so more blood flows near the skin surface, increasing heat loss. These responses oppose the rise in temperature and bring it back towards its normal narrow range, rather than keeping it at one absolutely fixed value. This is important because enzymes work most effectively within an optimum temperature range. If the body becomes too hot, enzymes can denature, changing the shape of their active sites, so important metabolic reactions are disrupted and cells cannot function properly.

Receptors in the skin detect the painful stimulus from the thorn and generate an electrical impulse. This impulse travels along a sensory neurone to the spinal cord, where it passes across synapses to a relay neurone and then to a motor neurone. The motor neurone carries the impulse to an effector muscle in the arm, which contracts and pulls the hand away from the thorn. The impulse is processed through the spinal cord rather than waiting for conscious processing by the brain, so the response is rapid. It is automatic and involuntary because it happens without conscious control.

The contraceptive implant is placed under the skin and releases a progesterone-like hormone into the blood over a prolonged period. This hormone reduces or prevents ovulation, so an egg is less likely to be released. It also makes the mucus in the cervix thicker, making it more difficult for sperm to enter the uterus. Therefore, sperm are less likely to meet an egg and fertilisation is less likely. A condom forms a physical barrier around the penis and prevents sperm from entering the vagina. This reduces the chance of sperm reaching an egg, so fertilisation is less likely to occur. Condoms can also reduce the transmission of some sexually transmitted infections.

Place equal numbers of similar, germinating bean seeds on damp cotton wool in several Petri dishes. Mark the initial direction of each root on the outside of the dish. Keep one group of dishes in the normal position, with the roots initially pointing downwards, and turn the other group through 90°, so that the roots initially point sideways relative to gravity. Keep the cotton wool damp but not covered with excess water. Keep the type and age of the seeds, temperature, light intensity, amount of water and time allowed for growth the same for both groups. After a set time, measure the angle each root has moved from its marked starting direction, and also measure its length. Use several seeds in each group and repeat the investigation. Calculate a mean angle, and mean root length if appropriate, for each arrangement and compare the results.