Feeding and Digestion in Amoeba: All living organisms require food to get energy for several metabolic, physiological, and physical processes. Food is also required to develop resistance against diseases. Amoeba is a unicellular, eukaryotic protozoan. All protozoans are believed to be the most primitive ancestors in the evolutionary history of animals. Like humans, Amoeba also cannot prepare their food and exhibits the heterotrophic mode of nutrition. Let’s read the complete article to understand the stepwise process of feeding and digestion in Amoeba.

Nutrition and Digestion

The use of nutrients by an organism for harvesting energy, building body substances for growth and development, and providing protection from diseases is called nutrition. The biochemical substances present in the food are called nutrients.
On the other hand, digestion is a step of nutrition that involves the breakdown of complex food molecules into simple food molecules.

Modes of Nutrition in Amoeba

Organisms that are unable to prepare their food and are totally dependent on others for food are called heterotrophs, and their mode of nutrition is called heterotrophic nutrition. Amoeba exhibits a holozoic mode of heterotrophic nutrition.
1. When organisms engulf the solid, complex food through their mouth or cell membrane and break it down inside the gut or cell, the mode is called holozoic nutrition or ingestive nutrition.
2. In Amoeba, the solid food particles are engulfed by the temporary finger-like projections called pseudopodia and further digested in the cell.
3. Paramecium, fishes, amphibians, reptiles, birds, mammals,  and humans also exhibit the holozoic mode of nutrition.

Fig: Amoeba

What is Feeding?

Feeding is the process of intake of food. Nutrition in animals depends on their feeding habits.
1. Simple organisms like Amoeba, Paramecium do not have any specific part or organ for the intake of food. Structures like pseudopodia, cilia help to sweep the food inside the cell.
2. Advanced organisms like mammals, reptiles have a specific opening called the mouth for the intake of food.

Feeding in Amoeba

Amoeba performs feeding with the help of the formation of pseudopodia. This process is called phagocytosis. It is a type of endocytosis that means ‘cell feeding’. In this process, once an Amoeba captures the food with the help of pseudopodia and encloses it in a vesicle called a phagosome, where the food is digested with the help of enzymes.

Steps Involved in Nutrition in Amoeba

The steps involved in nutrition in Amoeba are similar to those of complex organisms like humans. These steps are as follows:
1. Ingestion
2. Digestion
3. Absorption
4. Assimilation
5. Egestion

Fig: Steps of Nutrition in Amoeba

1. Ingestion

Ingestion means the intake of food. Amoeba does not have a specific opening (mouth) for the ingestion of food. The food particle is engulfed by the formation of pseudopodia (a temporary protrusion of the cell surface). The food is engulfed with a little amount of surrounding water to form a food vacuole. This food vacuole is also called the temporary stomach of Amoeba.

Depending upon the gross size of food particles, feeding in animals may be classified into two categories: macrophagy (ingesting large food particles as in chordates), microphagy (ingesting small food particles as in microscopic animals; Amoeba, Paramecium).

Fig: Ingestion in Amoeba

2. Digestion

Digestion is the process of the breakdown of complex organic food molecules (carbohydrates, proteins, fats) into simple food molecules. It is catalysed by digestive enzymes.
1. Digestion can be categorised into two types: Intracellular digestion (digestion within the cell)and extracellular digestion (digestion outside the cell in a cavity). Amoeba exhibits intracellular digestion.
2. In Amoeba, the digestive enzymes from the cytoplasm enter the food vacuoles and break down the food into smaller molecules that are suitable to be absorbed in the cell.
3. The two enzymes reported in Amoeba are amylase and proteinase.
4. Amylase breaks down the complex carbohydrates (polysaccharides) into simple carbohydrates (monosaccharides) called glucose.
5. Proteinase breaks down the protein molecules into amino acids.

Fig: Digestion in Amoeba

3. Absorption

Absorption is the process by which the digested food is absorbed within the cytoplasm of cells or through the cells lining the alimentary cavity.
The digested food present in the food vacuole is directly absorbed in the cytoplasm of Amoeba cells through the process of diffusion. The food vacuole gets degenerated after the absorption of food.

4. Assimilation

Assimilation is defined as a biological process in which the absorbed nutrients are utilised to satisfy the energy requirements of the body cells for several living activities.
In Amoeba, the absorbed food materials get converted into the constituents of protoplasm during assimilation. Glucose found in the protoplasm is used in respiration, and amino acids are used to build new proteins for growth. As a whole, assimilation of nutrients helps Amoeba to grow in size and reproduce.

5. Egestion

Egestion is the removal of undigested food materials from the body of an organism. Amoeba does not have any specific opening for the egestion. The undigested food remains stored in the old food vacuoles. It reaches the cell surface and fuses with the cell membrane at any site. The cell membrane then ruptures at the site of attachment of food vacuole, and the undigested food is thrown out of the body of the Amoeba. This process can be named exocytosis in Amoeba.

Comparative Study of Nutrition in Amoeba and Humans

All living organisms have arisen through the evolutionary process and show diversity. However, they share some similar basic morphological, anatomical, and physiological features. Based on this principle, nutrition in Amoeba and humans exhibit the following facts in common:
1. Amoeba and humans both exhibit holozoic mode of nutrition. However, humans have a specific opening called the mouth to engulf the food molecules, while Amoeba engulfs through pseudopodia.
2. The food vacuole performs a similar function to the stomach and small intestine in humans with respect to the digestion of food. However, the digestion in Amobea occurs in the cell and in humans, digestion takes place in the specific organs of the alimentary canal.
3. The digested food is absorbed into the cytoplasm of the Amoeba by the process of diffusion. This can be compared to the absorption of food in the blood (body fluid) of humans.
4. Egestion of undigested food is quite different in both. Humans remove the solid wastes through the anus, while Amoeba removes their wastes through the cell membrane.

Summary

Feeding involves the intake of food, and nutrition is the process of obtaining food in order to get energy for various living activities. Unicellular organisms also perform several life processes, hence requiring energy. Amoeba is a heterotroph that cannot prepare its food; therefore obtains the food from other sources, exhibiting holozoic mode of nutrition. This type of nutrition involves five steps, namely, ingestion, digestion, absorption, assimilation, and excretion. This article covers the detailed study of steps involved in nutrition in Amoeba and a comparison of nutrition in Amoeba with highly evolved mammals.

FAQs on Feeding and Digestion in Amoeba

Q.1. What is feeding in Amoeba?
Ans: Amoeba protrudes the pseudopodia around the food and engulfs the whole food particle. It is called feeding in Amoeba. It mainly feeds on bacteria and algae.

Q.2. How does Amoeba detect food?
Ans: Amoeba has a sense of ability to accept food particles. It detects the food with the help of pseudopodia.

Q.3. Where does Amoeba digest its food?
Ans: Amoeba digests the food inside the food vacuole that is called the temporary stomach of Amoeba.

Q.4. What is the use of false feet of Amoeba?
Ans: False feet called pseudopodia are used for locomotion and ingestion of food.

Q.5. What are the five stages of nutrition?
Ans: The five stages of nutrition are ingestion, digestion, absorption, assimilation, and egestion.

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