All living things need energy in one form or another. At the cellular level, energy is consumed in most metabolic pathways (usually in the form of ATP), particularly those responsible for building large molecules from smaller aggregates. Living organisms would not be able to get together complex organic compound molecules (proteins, lipids, nucleic and carbohydrate) without constant supply of energy.
Food web diagrams illustrate how energy flows directionally in ecosystems.can also indicate how efficiently organisms acquire energy, use it, and how much is left for other organisms in the food web.
Living things get energy in two ways: Autotrophs use light or chemical energy. Autotrophs are vital to ecosystems as they occupy the trophic level that contains the producers.
Photoautotrophs like photosynthetic plants, algae, and bacteria, are the energy source for most of the world’s ecosystems. Photoautotrophs collect the sun’s energy by converting it into chemical energy.
The rate tha photosynthetic producers absorb energy from the sun is gross primary productivity. However, not all of the energy consumed by the producers is available to the other organisms in the food web because the producers also need to grow and reproduce,
Net primary productivity is the energy that remains in the producers taking into account the metabolism and thermal dispersion of these organisms. Net productivity is therefore available for primary consumers at the next trophic level.
Chemoautotrophs are mainly bacteria and archaea found in rare ecosystems where sunlight is not available. For example, many chemoautotrophs in hydrothermal vents use hydrogen sulfide (H2S) released fromvents as a source of energy. This enables them to synthesize complex organic molecules, such as glucose, for their own energy and power up the ecosystem.