All organisms living in an ecosystem such as the African savanna, require energy and nutrients in order to carry out life’s activities such as growth, respiration, and reproduction. On the savannah, like nearly every ecosystem on Earth, sunlight provides the energy that powers life., while nutrients and the other essential building blocks of life such as carbon, nitrogen, phosphorous, and water enter the ecosystem from the non-living environment: the atmosphere, earth or sea from which the ecosystem arises. Solar energy continuously bombards the Earth, day after day, year after year, providing an essentially limitless source of energy for the Earth’s ecosystems. That energy flows through ecosystems, starting with the plants that convert the energy to chemical energy via photosynthesis. Energy captured by plants is then transferred to herbivores that graze on the plants. From there, part of the energy is transferred to predators as they eat the herbivores. Scavengers also obtain part of the energy that flooded into the ecosystem as sunlight as they pick at the remains left by predators. Finally, decomposers, breaking down what’s left to the molecular level, obtain the last remaining bits of energy from what started as beams of light. It is fortunate for life on Earth that the flow of energy form the sun is essentially limitless, because as the energy flows from plants to decomposer, each organism releases part of the energy they capture as heat that is lost to the atmosphere. This heat is forever lost for biological purposes within the ecosystem. Thus, for the flow of energy, and for the flow of life itself to continue, an outside source must constantly be injecting it with new energy.
Unlike solar energy, the nutrients essential for life are limited. The Earth has only so much carbon or nitrogen or phosphorous available for living organisms. For example, each year, photosynthesis in plants and other organisms capture about one-seventh of the carbon available in the atmosphere. If biological processes, such as cellular respiration, didn’t return most of this captured carbon back into the atmosphere, life as we know it on Earth would rapidly end, as there would be no carbon in the atmosphere for plants or other photosynthetic organisms to carry out life processes, such as capturing the energy in sunlight.
So, in order for life on Earth to continue, nutrients must be constantly recycled by the ecosystem. Thus, energy flows through ecosystems, while nutrients cycle through them.
The process by which energy flows through and nutrients cycle within an ecosystem play a major role in shaping the complex interactions between populations within the Earth’s great living communities.
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