Organisms that independently synthesize useful substances that they need for life are called autotrophic. This type of nutrition is also called "autotrophic." For these living organisms, an environment with the presence of carbon dioxide, water, inorganic salts and a certain energy source is sufficient for existence. Purple bacteria and green plants are fed through photosynthesis. Some bacteria have a type of nutrition in which they receive beneficial compounds through the oxidation of various inorganic substances, such as hydrogen sulfide and ammonia. Most often, the source of energy is sunlight.
Creatures that use heterotrophic nutrition are unable to synthesize the substances they need on their own. They are forced to use ready-made connections. Therefore, the heterotrophic type of nutrition is due to autotrophs or the remains of other organisms. Thus, the food chain is formed. Creatures that use this type of food include most bacteria, fungi, and all animals.
There are various types of heterotrophs. Some creatures can eat others or parts of them, and then digest. This is a holozoic type of food. Such creatures constantly hunt to feed themselves. Cats eat mice and birds, frogs eat mosquitoes and flies, owls feed on rodents, etc. Organisms having this type of nutrition are endowed with certain sensory organs, muscular and nervous instruments. This arsenal helps them find and catch prey. The transformation of food into molecular compounds that the body can absorb occurs in the digestive system.
Some plants (sundew, Venus flytrap), in addition to photosynthesis, can still get food through hunting. They catch, lure and digest various insects, as well as some small animals. Such plants are called "insectivores."
Herbivores feed on plant foods and get energetically valuable compounds from its cells that are synthesized by green plants.
Another group of holozoic animals (carnivorous predators) uses a type of food in which they eat herbivores or other predators. Some of them are omnivorous and can eat both plant and animal food.
Initially, all heterotrophic creatures receive energetically valuable substances from autotrophs. Green plants synthesize these compounds by photosynthesis. Sunlight is the main source of energy. Without it, there would be no life on the planet, since it is the basis of all nutrients.
Most varieties of bacteria, yeast and molds cannot swallow whole foods. They feed through cell membranes. This type of heterotrophic nutrition is called saprophytic. These creatures can only live in places where there are plant or animal organisms that decompose, or a significant amount of their metabolic products.
