(a) Define food chain.
(b) Describe the energy flow within a terrestrial ecosystem.
(c) Highlight three ways by which nitrogen cycle is maintained in the terrestrial ecosystem.
Explanation
(a) A food chain is a linear network of links in a food web starting from producer organisms and ending at apex predator species, detritivores, or decomposer species. A food chain also shows how the organisms are related with each other by the food they eat. Each level of a food chain represents a different trophic level.
(b) Our ecosystem is maintained by the cycling energy and nutrients obtained from different external sources. At the first trophic level, primary producers use solar energy to produce organic material through photosynthesis. The herbivores at the second trophic level, use the plants as food which gives them energy.
(c) The terrestrial nitrogen (N) cycle comprises soil, plant and animal pools that contain relatively small quantities of biologically active N, in comparison to the large pools of relatively inert N in the lithosphere and atmosphere, but that nevertheless exert a substantial influence on the dynamics of the global biogeochemical N cycle. After carbon (ca. 400 g kg−1) and oxygen (ca. 450 g kg−1), N is the next most abundant element in plant dry matter, typically 10–30 g kg−1. It is a key component of plant amino and nucleic acids, and chlorophyll, and is usually acquired by plants in greater quantity from the soil than any other element. Plant N provides the basis for the dietary N (protein) of all animals, including humans.