An autotroph is an organism that can make its own food using light, water, carbon dioxide, or other chemicals. Because autotrophs make their own food, they are sometimes called producers. Plants are the most familiar type of autotrophs, but there are many different types of autotrophic organisms. algae, which live in water and whose largest forms are known as algae, are autotrophs. Phytoplankton, tiny organisms that live in the ocean, are autotrophs. some types of bacteria are autotrophs. most autotrophs use a process called photosynthesis to make their food. In photosynthesis, autotrophs use energy from the sun to convert water from the soil and carbon dioxide from the air into a nutrient called glucose. glucose is a type of sugar. glucose gives energy to plants. Plants also use glucose to make cellulose, a substance they use to grow and build cell walls. All plants with green leaves, from the smallest mosses to towering fir trees, synthesize or create their own food through photosynthesis. algae, phytoplankton, and some bacteria also photosynthesize. some rare autotrophs make food through a process called chemosynthesis, rather than through photosynthesis. autotrophs that perform chemosynthesis do not use the sun’s energy to produce food. instead, they make food using the energy of chemical reactions, often by combining hydrogen sulfide or methane with oxygen. Organisms that use chemosynthesis live in extreme environments, where the toxic chemicals needed for oxidation are found. for example, bacteria that live in active volcanoes oxidize sulfur to make their own food. bacteria capable of chemosynthesis have been found in hot springs in yellowstone national park in the united states in the states of wyoming, idaho and montana. bacteria that live in the deep ocean near hydrothermal vents also produce food through chemosynthesis. A hydrothermal vent is a narrow crack in the seabed. seawater seeps through the crack onto the hot, partially molten rock below. the boiling water then circulates back to the ocean, loaded with minerals from the hot rock. these minerals include hydrogen sulfide, which bacteria use in chemosynthesis. autotrophic bacteria that produce food through chemosynthesis have also been found in places on the seafloor called cold seeps. In cold seeps, hydrogen sulfide and methane percolate from below the seafloor and mix with ocean water and dissolved carbon dioxide. autotrophic bacteria oxidize these chemicals to produce energy.
autotrophs in the food chainto explain a food chain, a description of which organisms eat which other organisms in nature, scientists group organisms into trophic or nutritional levels. there are three trophic levels. because autotrophs do not consume other organisms, they are the first trophic level. autotrophs are eaten by herbivores, organisms that consume plants. herbivores are the second trophic level. carnivores, creatures that eat meat, and omnivores, creatures that eat all kinds of organisms, are the third trophic level. herbivores, carnivores, and omnivores are all consumers: they consume nutrients rather than manufacture them themselves. herbivores are primary consumers. carnivores and omnivores are secondary consumers. all food chains begin with some type of autotroph (producer). for example, autotrophs like grasses grow on rocky mountains. Mule deer are herbivores (primary consumers), which feed on autotrophic grasses. carnivores (secondary consumers) such as cougars hunt and consume deer. in hydrothermal vents, the producers of the food chain are autotrophic bacteria. primary consumers, such as snails and mussels, consume autotrophs. carnivores such as octopuses consume snails and mussels. an increase in the number of autotrophs will generally lead to an increase in the number of animals that eat them. however, a decline in the number and variety of autotrophs in one area can devastate the entire food chain. If a wooded area is burned in a wildfire or cleared to build a shopping mall, herbivores such as rabbits can no longer find food. some of the rabbits may move to a better habitat and some may die. without the rabbits, foxes and other carnivores that feed on them also lose their food source. they too must move to survive.
