Holozoic Nutrition

Holozoic nutrition is a type of heterotrophic nutrition that is characterised by the ingestion and internal processing of liquids or solid food particles. Protozoa, such as amoebas, and most of the free living animals, such as humans, exhibit this type of nutrition.

In Holozoic nutrition, energy and organic building blocks are obtained by ingesting and then digesting other organisms or pieces of other organisms, including blood and decaying organic matter. 

There are several stages of Holozoic nutrition, which often occur in separate compartments within an organism (such as the stomach and intestines):

1. Ingestion :

It is the consumption of food by the organism. It varies from one organisms to another. 

For example:

• amoeba ingests with the help of Pseudopodia.
• Paramecium uses cilia.
• Butterfly does it using its feeding tube.
• Python swallows smaller animals.
• Human use their mouth etc.

2. Digestion :

It involves breaking down the complex molecules into simpler substance. Here, food is broken down mechanically through chewing or chemically through the release of acids and enzymes in the alimentary canal.

In humans, 

• The process of digestion starts in the mouth.
• The teeth help in chewing the food and breaking it into smaller pieces.
• The saliva in the mouth has a digestive enzyme called salivary amylase (also called Ptyalin) that help in moistening the food and breaking it into simpler compounds.
• The food is then pushed by the peristaltic movement of the food pipe (Oesophagus) into the stomach.
• In the stomach, only the digestion of proteins takes place as it has an acidic environment due to the secretion of Hydrochloric acid (HCL).
• The pepsin enzyme secreted in the stomach converts the proteins into Peptones that are shorter chains of amino acid.
• Then, the partially digested food is pushed into the small intestine where all the nutrients are converted into their respective simpler units.

    Starch àSugar à Glucose                         by the action of enzyme amylase

    Protein à Amino acids                               by the action of enzyme protease

Fats à Fatty acids and glycerol                 by the action of enzyme lipase

This completes the process of digestion as all nutrients have been converted into their simpler form that are now absorbable into the blood that carries these nutrients to various in the body.

3. Absorption :

• The absorbable nutrients are taken into the blood and to other parts of the body. 
• The absorption of the food nutrients starts in small intestine that has finger-like projections called villi on this inner surface.The villi increases the surface area for absorption and facilitate the absorption of nutrients into the blood.
• The remaining food is then passed into the large intestine where the water is absorbed into the blood from the undigested food and the undigested food is passed through the rectum part of the large intestine, and finally, through the anus.

4. Assimilation :

• The utilisation of the nutrients for the metabolic processes of the body is called Assimilation.

5. Egestion :

• The process of eliminating the undigested food from the body is called Egestion.