Which biotic component of an ecosystem is present in the greatest number?

The correct answer is B, Producers. Producers, the green plants and algae, are the most numerous living part of an ecosystem because every other organism depends on them for food. They make their own food by photosynthesis using sunlight, so they form the first trophic level of every food chain. Only about 10 per cent of the energy passes from one level to the next (Lindeman's ten per cent law), so each higher level can support fewer organisms. This gives the upright pyramid of numbers in a grassland: many grass plants, fewer grasshoppers, fewer frogs, and very few snakes and hawks. A is wrong because primary consumers, the herbivores, feed on producers and are fewer than them. C is wrong because secondary consumers, the small carnivores, are fewer still. D is wrong because tertiary consumers, the top carnivores such as the tiger or eagle, are the fewest of all. Exam tip: Producer → primary consumer → secondary consumer → tertiary consumer; about 90 per cent of energy is lost at each step; in a single-tree ecosystem the pyramid of numbers is inverted.