Ecology Organisms and Their Interactions Practice Questions

1. a. Each step is a trophic level, which represents the feeding position or level where an organism exists in a particular food chain or food web. The word trophic refers to feeding (or eating).

2. d. In each step of a food chain, only 10% of the energy moves from one trophic level to the next. If the grass represents 100% of the energy available, then the rabbit would only have 10% available, and the fox would then only have 1% available. In other words, it would take 100 pounds of grass to support ten pounds of rabbit and then one pound of fox.

3. c. An herbivore is an animal that eats plants. Plants are producers in food chains, and any organism that eats plants is a consumer. Animals that eat other animals are also consumers. All animals are some kind of consumer because they cannot make their own food. First-order consumers such as herbivores are at the second level of a food chain (plants are at the first level), but they are the first level of consumer. Second-order consumers are other animals that eat herbivores. Third trophic-level organisms are another way of saying second-order consumers (they are at the third trophic level after herbivores and plants).

4. b. Food webs are complex groupings of interacting food chains. Organisms may play different roles in different food chains. Food webs with a number of diverse organisms are considered more stable than single food chains.

5. b. Primary consumers are the first level of consumers, but also the second trophic level. The first trophic level contains the producers (plants).