What is Holozoic Nutrition? Stages and Features

The Holozoic nutrition Is a nutritional method that involves the ingestion of liquid or solid organic material, its digestion, absorption and assimilation for use as a source of energy in the body.

Holozoic nutrition includes taking the complex substances and converting them into simpler forms. For example, proteins can be divided into amino acids.

Holozoic nutrition

This method suggests Phagocytosis Where the cell membrane completely surrounds a food particle. Most free live animals, including humans, exhibit this type of nutrition.

In this mode of nutrition, the food may be a small bacteria, a plant or an animal. Holozoic nutrition is the process used by most animals. In this process, food that is ingested as a solid particle is digested and absorbed.

Holozoic nutrition can also be classified in terms of the source of food: herbivores, such as cows, obtain food from plants; Carnivores, like wolves, obtain nutrients from other animals; Omnivores, like man, use both plants and animals to eat.

Stages of the holozoic nutrition process

There are five stages in the holozoic nutrition process used by most of the higher invertebrates and vertebrates.

1. Ingestion

Ingestion is the act of consuming any substance, whether liquid, food, medication, poisons, pathogenic bacteria or even nondigestible nutrients.

In short, ingestion refers simply to the act of introducing any substance into the digestive system .

Food is introduced as large or small particles. This can be by specialized organs such as the mouth in higher animals or by the general surface of the body with the aid of structures such as pseudopodia in lower organisms (such as amoebas). Ingestion of pseudopods is called phagocytosis.

2. Digestion

Digestion is defined as the process by which complex food molecules are broken down into simpler molecules, so that they can be absorbed by the body. Digestion can be mechanical or chemical.

In mechanical digestion, food is physically decomposed into smaller particles by processes such as mastication.

Chemical digestion, for its part, makes use of certain chemicals called enzymes. They are proteins that help in the simplification of the alimentary matter.

The required enzymes are secreted by the organism itself depending on the type of food to be digested.

Enzymes break covalent bonds in food molecules and release energy. This reaction is called chemically hydrolysis And is the decomposition of a bond by the addition of the water molecule. The enzymes that catalyze these reactions are, therefore, called hydrolases.

Digestion converts food into soluble form. This is done in order to absorb food into the cells. Foods such as glucose and vitamin C , Which are already small and soluble in water, do not need to undergo digestion. They can enter directly into the cells.

Digestion can take place outside (extracellular) cells or within (intracellular) cells. In unicellular organisms the digestion is intracellular with the enzymes present in the vesicles.

In more advanced multicellular forms, the digestive enzymes are secreted outside in the surrounding environment. The digested products are absorbed back into the cell.

In upper and vertebrate invertebrates, digestion takes place in a separate specialized channel called the alimentary canal.

In lower organisms such as Hydra, ingestion and excretion take place through the same opening. Features such as ingestion and excretion with different openings and each portion of the canal with specific enzymes directed to specific types of foods increase the efficiency of the digestive system.

3. Absorption

This involves the absorption of food in the soluble form from the region of digestion to the tissues or into the bloodstream that transports it to the different tissues. This occurs through cell membranes. Absorption may be passive or active.

Passive absorption is through diffusion or osmosis without using energy. It takes place in both directions. For example, water is absorbed by osmosis. Active absorption needs energy and can be inhibited by poisons such as cyanide. It only takes place in one direction.

The small intestine is 5 to 6 meters long, and most of the chemical digestion occurs within the first meter. Once the food has been digested into smaller molecules, the absorption can be carried out.

Millions of small finger-like structures, called villi, project inwardly from the lining of the small intestine.

These structures greatly increase the contact surface of the products of the digestion with the small intestine, allowing their rapid absorption into the bloodstream. Once absorbed, they are transported to the liver via the hepatic portal vein.

4. Assimilation

The digested food is assimilated by the cytoplasm By diffusion. Food vacuoles constantly move in the cytoplasm to deliver the digested food to each part of the body through the cells.

Assimilation involves the use of the nutrients that have been purchased from foods for the various functions of the body.

5. Excretion

By the end of the small intestine, all digested food products, along with the minerals and vitamins that are useful for the body, should have been removed from the aqueous contents, ie they should have been assimilated to benefit the body.

What remains, consists of the indigestible components of foods such as cellulose from the consumption of herbal foods. These materials are then passed to the large intestine.

In the large intestine the following functions are performed:

  • Recover water and electrolytes (sodium, chloride) from indigestible food.
  • Form and store stool.
  • Fermenting part of the indigestible food material by bacteria.
  • Maintain a bacterial population.

As the undigested material accumulates in the rectum, it stimulates a response that leads to the removal of waste through the anus.


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