Just as energy flows through an ecosystem, matter also moves from organism to organism and from organisms to the environment. Using either a kelp forest or a hydrothermal vent ecosystem as an example, explain how carbon can move through the organisms in that ecosystem.

Energy is transferred through an ecosystem in steps, making up a food chain or a food web. At the bottom of the chain are the primary producers, which absorb sunlight and use the light energy to convert carbon dioxide and water into carbohydrates (long chains of sugar molecules) and eventually into other biochemical molecules, by photosynthesis.

The primary producers support the consumers—organisms that ingest other organisms as their food source. Finally, decomposers feed on decaying organic matter, from all levels of the web. Decomposers are largely microscopic organisms (microorganisms) and bacteria.

The food web is really an energy flow system, tracing the path of solar energy through the ecosystem. Solar energy is absorbed by the primary producers and stored in the chemical products of photosynthesis. As these organisms are eaten and digested by consumers, chemical energy is released. This chemical energy is used to power new biochemical reactions, which again produce stored chemical energy in the consumers' bodies.

Energy is lost at each level in the food web through respiration. You can think of this lost energy as fuel burned to keep the organism operating. Energy expended in respiration is ultimately lost as waste heat and cannot be stored for use by other organisms higher up in the food chain. This means that, generally, both the numbers of organisms and their total amount of living tissue must decrease greatly up the food chain. In general, only 10 to 50 percent of the energy stored in organic matter at one level can be passed up the chain to the next level. Normally, there are about four levels of consumers.