In 1931 a scientist was pouring the powdered form of a chemical called PTC into a bottle. A small amount of the powder accidentally blew into the air. A short time later another scientist working in the same room said that she had a bitter taste in her mouth from the powder in the air.

1. (a)Describe, with reference to named components of the nervous system, the nervous pathway that led to the scientist detecting that the powder tasted bitter.[4]
2. (b)The scientist pouring the powder did not detect any bitter taste. It was later found that inheritance of two forms of the same gene determine if a person is able to detect a bitter taste from PTC or not.
3. (b)(i)State the term used for different forms of the same gene.[1]
4. (b)(ii)Several years afterwards, it was found that environmental factors cause people to detect a range of different strengths of bitter taste from PTC. State the type of variation now known to be shown by this characteristic.[1]
5. (c)Chemicals similar to PTC with a bitter taste are produced by some plants to prevent them from being eaten. Animals that eat only plants have fewer genes that enable them to detect chemicals that taste bitter than animals that eat both plants and animals.
6. (c)(i)State the trophic level of plants in a food web.[1]
7. (c)(ii)State the term used for animals that eat only plants.[1]
8. (c)(iii)Suggest why animals that eat only plants have fewer genes that enable them to detect chemicals that taste bitter than animals that eat both plants and animals.[2]