Aquatic
In aquatic systems, primary production is typically measured using one of six main techniques:[11]
vAutotrophs are fundamental to the food chains of all ecosystems in the world. They take energy from the environment in the form of sunlight or inorganic chemicals and use it to create energy-rich molecules such as carbohydrates. This mechanism is called primary production. Other organisms, called heterotrophs, take in autotrophs as food to carry out functions necessary for their life. Thus, heterotrophs — all animals, almost all fungi, as well as most bacteria and protozoa — depend on autotrophs, or primary producers, for the energy and raw materials they need. Heterotrophs obtain energy by breaking down organic molecules (carbohydrates, fats, and proteins) obtained in food. Carnivorous organisms rely on autotrophs indirectly, as the nutrients obtained from their heterotroph prey come from autotrophs they have consumed.
Most ecosystems are supported by the autotrophic primary production of plants that capture photons initially released by nuclear fusion reactions in the sun. The process of photosynthesis splits a water molecule (H2O), releasing oxygen (O2) into the atmosphere, and reducing carbon dioxide (CO2) to release the hydrogen atoms that fuel the metabolic process of primary production. Plants convert and store the energy of the photon into the chemical bonds of simple sugars during photosynthesis. These plant sugars are polymerized for storage as long-chain carbohydrates, including other sugars, starch, and cellulose; glucose is also used to make fats and proteins. When autotrophs are eaten by heterotrophs, i.e., consumers such as animals, the carbohydrates, fats, and proteins contained in them become energy sources for the heterotrophs.[3] Proteins can be made using nitrates, sulfates, and phosphates in the soil.[