Which one of the following group of organisms forms a food chain?

The correct answer is B, Grass, goat and human. In this chain each organism is eaten by the next: grass, a producer, is eaten by the goat, a herbivore, and the goat is eaten by humans, so energy passes in a straight line. A food chain always begins with a green plant that makes food by photosynthesis, the producer. It then moves to a primary consumer that eats plants, and then to a secondary consumer that eats the herbivore. Only about 10 per cent of the energy at one level reaches the next, which is why food chains rarely have more than four or five links. Option A is wrong because humans do not eat grass and fish do not eat humans, so the order does not form a feeding sequence. Option C is wrong because a tree cutter does not eat the tree, so there is no transfer of food energy between them. Option D is wrong because goat and cow are both herbivores; a cow does not eat a goat, and there is no producer at the start. Exam tip: producer → herbivore → carnivore; grass → goat → human; about 10% energy passes up each level.