B1: Extended Answers

The stimulus is detected by sensory receptors. Impulses travel along sensory neurone to the spinal chord, bypassing the conscious part of the CNS. The impulse is diffused as a chemical across synapse via relay neurone. Impulse goes to effector (muscle or gland) via motor neurone and reflex takes place.

(Six Marks)

Gravity causes unequal redistribution of auxin on the of the side of the  stem in the shade. Auxin stimulates growth in the cells on the shaded side, resulting in the stem bending and growing upwards.

(Four Marks)

Respiration releases energy. Energy is also lost in the animals' faeces or urine. Some energy is also lost when animals move around or is given off as heat to its surroundings. When animals / plants die, some are decomposed by detritus feeders. However, not all of an animal may be eaten (bones etc), so some energy may end up being wasted.

(Six Marks)

There is a genetic mutation in the bacteria. Whilst most are killed by the antibiotic, this mutation causes some bacterial cells to survive the antibiotic and become resistant. These bacteria then go on to breed.

(Three Marks)

Organisms in a species may show variation because mutations occur within individuals. This results in individuals with characteristics most suited to their environment being more likely to survive and breed, consequently passing their genes on to their offspring.

(Four Marks)

Carbon dioxide is released into the atmosphere by plants, animals, and microorganisms during respiration. Plants remove carbon doixide  from the atmosphere during photosynthesis. The animals eat plants to get energy to respire. When animals and plants die, they are decomposed by microorganism (detritus feeders), which also respire. Combustion (burning) of fossil fuels also releases carbon doixide into the atmosphere.