Nutrition is a unique process by which the body receives the necessary energy and nutrients for cellular metabolism, repair and growth.
Heterotrophs: general characteristics
Heterotrophs are those organisms that use organic food sources. They cannot create organic substances from inorganic substances, as autotrophs (green plants and some prokaryotes) do in the process of photo- or chemosynthesis. That is why the survival of the described organisms depends on the activity of autotrophs.
It should be noted that heterotrophs are humans, animals, fungi, as well as part of plants and microorganisms that are incapable of photo- or chemosynthesis. I must say that there is a certain type of bacteria that use the energy of light to form their own organic substances. They are photoheterotrophs.
Heterotrophs get food in a variety of ways. But they all come down to the main three processes (digestion, absorption and assimilation), in which complex molecular complexes are broken down into simpler ones and absorbed by tissues with subsequent use for the needs of the body.
Classification of heterotrophs
All of them are divided into 2 large groups - consumers and decomposers. The latter are the final link in the food chain, as they are able to convert organic compounds into minerals. Consumers are those organisms that use ready-made organic compounds that were formed during the life of autotrophs without their final transformation into mineral residues.
Besides this, heterotrophs are saprophytes or parasites. Saprophytes feed on organic compounds of dead organisms. These are most animals, yeast, molds and cap fungi, as well as bacteria that cause fermentation and decay processes.
Parasites feed on organic compounds of living organisms. These include some protozoa, parasitic worms, blood-sucking insects and mites. This group also includes viruses and pathogenic bacteria, parasitic heterotrophic plants (for example, mistletoe) and parasitic fungi.
Nutrition of heterotrophic organisms
According to the nature of nutrition, heterotrophs are very diverse. So, among them there are herbivorous or carnivorous species, parasites and predators, organisms that consume dead plant fibers or animal corpses as food, as well as such forms that use dissolved organic substances for their nutrition.
If we talk about the types of heterotrophic nutrition, we should mention the holozoic species. Such nutrition is usually characteristic of animals and includesthe following steps:
- Catching food and swallowing it.
- Digestion. It involves breaking down organic molecules into smaller particles that dissolve more easily in water. It should be noted that food is first mechanically ground (for example, with teeth), after which it is exposed to special digestive enzymes (chemical digestion).
- Suction. Nutrients either immediately enter the tissues, or first into the blood, and then with its current to various organs.
- Assimilation (the process of assimilation). It lies in the use of nutrients.
- Excretion - excretion of end products of metabolism and undigested food.
Saprotrophic organisms
As already noted, organisms that feed on dead organic residues are called saprophytes. To digest food, they secrete the appropriate enzymes, and then absorb the substances resulting from this extracellular digestion. Mushrooms - heterotrophs, which are characterized by a saprophytic type of nutrition - these are, for example, yeast or fungi Mucor, Rhizppus. They live on a nutrient medium and secrete enzymes, and the thin and branched mycelium provides a significant absorption surface. In this case, glucose goes to the process of respiration and provides the fungi with energy, which is used for metabolic reactions. It must be said that many bacteria are also saprophytes.
It should be noted that many compounds that are formed during the nutrition of saprophytes are not absorbed by them. These substances enter the environment, after which they can be used by plants. That is why the activity of saprophytes plays an important role in the circulation of substances.
The concept of symbiosis
The term "symbiosis" was introduced by the scientist de Bari, who noted that there are associations or close relationships between organisms of different species.
So, there are such heterotrophic bacteria that live in the digestive canal of herbivorous chewing animals. They are able to digest cellulose by feeding on it. These microorganisms can survive in the anaerobic conditions of the digestive system and break down cellulose into simpler compounds that the host animals can digest and assimilate on their own. Another example of such a symbiosis is plants and root nodules of bacteria of the genus Rhizobium.
If we talk about the coexistence of various organisms, we should mention such a phenomenon as parasitism. Under it, one of them (the parasite) benefits from such coexistence, while the other only harms (the host). So, the parasite in this case extracts not only nutrients from the one on which it lives, but also acquires a shelter on it.
Parasites living on the external surfaces of the host are called ectoparasites (fleas, ticks or leeches). They lead not only a parasitic way of life. The internal ones are obligatory. They are characterized only by a parasitic existence (such as tapeworm, plasmodia or liver fluke).
To summarize, it can be argued thatheterotrophs are an extremely broad group of living beings that not only interact with each other, but are also able to influence other organisms.
