Heterotrophs are either secondary or tertiary consumers in the food chain. Carbon fixation is the process of converting inorganic carbon (CO2) into organic materials such as carbohydrates, which is usually accomplished by photosynthesis. Autotrophs are organisms that can use carbon fixation to produce their own sustenance.
Heterotrophs come in two varieties. Photoheterotrophs use light for energy, but because they cannot use carbon dioxide as their only carbon source, they must rely on organic matter from their surroundings. Photoheterotrophs include Heliobacteria and some Proteobacteria. Heterotrophs can use all the energy they consume for growth, reproduction and other biological functions by ingesting fewer carbon molecules.
Examples of heterotrophs
Herbivores, or primary consumers, are heterotrophs that eat plants for nutrition. Through cellular respiration, complex organic molecules (carbon dioxide) are converted into energy (ATP) during photosynthesis. ATP is often found in the form of simple carbohydrates (monosaccharides) such as glucose and more complex carbohydrates (polysaccharides) such as starch and cellulose. Due to the presence of amylase, an enzyme released by the salivary glands and pancreas, starch is easily broken down by most mammals.
Herbivores include cows, sheep, deer and other ruminant animals that ferment food in specialized chambers within their stomachs that house symbiotic microbes. Fruit-eating animals, such as birds, bats and monkeys, are also herbivores, although they are called frugivores. Most plant material is composed of difficult-to-digest cellulose, but the plant’s nectar is largely composed of simple sugars and is consumed by substances known as nectarines, such as hummingbirds, bees, butterflies, and moths.
Energy that is carried through the food chain first from inorganic chemicals and then to organic compounds to be used as energy by autotrophs, is stored within the body of heterotrophs known as primary consumers.
The energy used as fuel by predators comes mainly from lipids (fats) that herbivores have stored in their bodies. Small amounts of glycogen (a polysaccharide of glucose that serves as a type of long-term energy storage) are stored in the liver and muscles and can be used for energy intake by carnivores, although supplies are limited.
Secondary consumers include heterotrophs that eat herbivores such as snakes, birds and frogs (usually insectivores) and marine animals that ingest zooplankton such as small fishes and jellyfish. They can also be tertiary consumers or predators that prey on other carnivores such as lions, hawks, sharks and wolves.
Carnivores can also be scavengers, which are animals such as vultures or cockroaches that feed on dead animals.
Fungi are primitive organisms. Mushrooms, mold and mildew are some examples. Some are found in the human body. Only about half of all fungi are dangerous. Fungi are heterotrophic organisms that feed by absorption rather than swallowing their food like other animals. Fungi have root-like structures known as hyphae that grow and form a network in the substrate on which the fungus feeds. These hyphae release digestive enzymes, which break down the substrate and allow nutrients to be digested. Fungi live on a wide variety of substrates such as wood, cheese, or meat, while most of them specialize in a narrow range of food sources; Some fungi are very specialized, and can only derive nutrition from a single species. Many fungi are parasitic, meaning they feed without killing their hosts. Saprobic fungi recycle nutrients from dead or decaying matter, making them available as nutrients to mushroom-eating animals. The role of fungi as decomposers and recyclers at all trophic levels of the nutrient cycle is important within ecosystems, but they are also commercially important to humans. Many fungi are involved in the manufacture of human food. Fungi are also used by humans for pest management. The fungus can also be used to make citric acid, antibiotics, and human hormones.