Nutrition is a kind of process in which the body receives the necessary energy and nutrients for cellular metabolism, repair and growth.
Heterotrophs: general characteristic
Heterotrophs are those organisms that use organic sources of nutrition. They cannot create organic matter from inorganic matter, 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. These are photoheterotrophs.
Heterotrophs receive food in various ways. But they all boil 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, followed by use for the needs of the body.
Heterotroph classification
All of them are divided into 2 large groups - consumers and reducers. The latter are the final link in the food chain, as they are able to turn organic compounds into minerals. Consumables are those organisms that use ready-made compounds of organics that were formed during the life of autotrophs without their final conversion to mineral residues.
In addition, heterotrophs are saprophytes or parasites. Saprophytes feed on the organic compounds of dead organisms. This is the majority of animals, yeast, molds and cap mushrooms, as well as bacteria that cause fermentation and decay.
Parasites feed on organic compounds of living organisms. These include some of the simplest, parasitic worms, blood-sucking insects and ticks. This group also includes viruses and pathogenic bacteria, parasitic heterotroph plants (e.g. mistletoe) and parasite fungi.
Nutrition of heterotrophic organisms
By the nature of their 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 carcasses 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 form. Such nutrition, as a rule, is characteristic of animals and includes the following steps:
- Grabbing food and swallowing it.
- Digestion. It involves the breakdown of organic molecules into smaller particles that dissolve more easily in water. It should be noted that first mechanical grinding of food (for example, with teeth) takes place, after which it is exposed to special digestive enzymes (chemical digestion).
- Suction. Nutrients either immediately enter the tissues, or first into the bloodstream, and then with its current into various organs.
- Assimilation (assimilation process). It consists in the use of nutrients.
- Excretion - excretion of end products of metabolism and undigested food.
Saprotroph organisms
As already noted, organisms that feed on dead organic residues are called saprophytes. To digest food, they secrete the corresponding enzymes, and then absorb the substances resulting from such extracellular digestion. Mushrooms are heterotrophs that are characterized by a saprophytic type of nutrition - for example, yeast or Mucor, Rhizppus mushrooms. They live on a
nutrient medium and secrete enzymes, and a thin and branched mycelium provides a significant absorption surface. In this case, glucose goes to the process of respiration and providing the mushrooms 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 mule animals. They are able to digest cellulose, eating it. These microorganisms can survive under the anaerobic conditions of the digestive system and break down cellulose into simpler compounds that host animals can independently digest and assimilate. 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 a phenomenon such as parasitism. Under him, one of them (the parasite) benefits from such coexistence, while the other only harms (the host). So, in this case, the parasite extracts from the one on whom it lives, not only nutrients, but also takes refuge on it.
Parasites living on the outer surfaces of the host are called ectoparasites (fleas, ticks or leeches). They lead not only a parasitic lifestyle. Internal ones are obligate. They are characterized only by a parasitic existence (for example, pork tapeworm, plasmodium, or liver fluke).
To summarize, it can be argued that heterotrophs are an extremely wide group of living creatures that not only interact with each other, but are also able to influence other organisms.