Energy Transfer

A food web consists of several components; primary producers, primary consumers, secondary consumers, tertiary consumers, and so on. Primary producers include green plants and are the foundation of the food web. Through photosynthesis, primary producers capture some of the Sun's energy. The net rate of photosynthesis, or net primary productivity (NPP), is equal to the rate of photosynthesis minus the rate of respiration of plants. In essence, NPP is the profit for the primary producer, after their energy costs associated with respiration are accounted for. NPP determines plant growth and how much energy is subsequently available to higher trophic levels.

Primary consumers are organisms that feed directly on primary producers, and these comprise the second trophic level of the food web. Primary consumers are also called herbivores, or plant-eaters. Secondary consumers are organisms that eat primary consumers, and are the third trophic level. Secondary consumers are carnivores, or meat-eaters. Successive trophic levels include the tertiary consumers, quaternary consumers, and so on. These can be either carnivores or omnivores, which are both plant- and animal-eaters, such as humans.