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What is Amoeba?

Last updated date: 19th Mar 2023
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Amoeba is a unicellular protozoa whose digestion takes place in the food vacuole. The food ingested is engulfed by pseudopodia through the process of phagocytosis. The food vacuoles then fuse with lysosomes to form phagolysosomes that contain the enzymes essential for breaking down food particles.

Modes of Nutrition

Nutrients are reported to provide the energy required for carrying out our vital functions. Broadly, the nutrition in living organisms can be classified into two types, autotrophic and heterotrophic.

In the autotrophic mode of nutrition, the organisms utilize simple inorganic molecules like water and carbon dioxide to synthesize food with the air of light and chlorophyll on their own. Plants, algae, and cyanobacteria can synthesize their own food.

In the case of heterotrophic nutrition, organisms depend on others for their nutrition as they are incapable of synthesizing their food, unlike plants. Fungi and animals, including humans, are heterotrophs, which can again be classified into different groups depending on the type of their environment and adaptations.

Those who eat plants are called herbivores, and those feeding on animals are called carnivores. Few organisms feed on both, and they are called omnivores. Heterotrophs are again classified into 3 groups based on their mode of nutrition. First is the parasites that include leeches, ticks, Saprophytes (e.g. mushrooms), and Holozoic (e.g. humans, dogs) are the other groups.

Digestion in Amoeba

Amoeba is a eukaryotic organism that is classified as protozoa. All the protozoans have the special characteristics of living inside the host as parasites; hence they are also known as primitive relatives of animals.

Holozoic nutrition is the mode of nutrition in these organisms. The process of digestion in amoeba involves ingestion, digestion, absorption, assimilation, and egestion. Amoeba being a single-celled organism is reported to have intracellular digestion, which is facilitated by digestive enzymes that break down the large insoluble particles into simple ones. The finger-like projections called pseudopodia help in this process. The pseudopodia extend and engulf the food particle.

Amoeba digests their food in the food vacuole. The food vacuole is formed due to ingestion and its combination with lysosomes. The digested and absorbed food provides energy, and the excess food is stored as glycogen. The amoeba contains membrane-bound organelles such as lysosomes that contain hydrolytic enzymes like proteases, nucleases, and lipases. After the process of digestion, the enzymes are egested out. The process of engulfing liquid in amoeba is called pinocytosis.

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Amoeba Diagram

Process of Nutrition in Amoeba

Nutrition in an Amoeba takes place through a process also known as phagocytosis. In this process, the entire amoeba engulfs the food/bacteria. It shows heterotrophic nutrition, characterized by the internalization of liquids or solid food. Nutrition involves the following steps. ingestion, digestion, absorption, assimilation and egestion of food. The body surface of the amoeba takes part in the process as they do not have any specialized organs for nutrition.

The first step is ingestion which is the process of engulfing food by swallowing inside the body through the process of phagocytosis. Food vacuoles are formed as a result of the internalization of food. The next step is digestion, where the mechanical and chemical breakdown of the ingested food takes place with the aid of digestive enzymes.

Absorption is the process of absorption of nutrients from digested food. The excess food is later stored as glycogen or lipids for future use. Assimilation is the process of oxidation of food to gain the energy required for survival. Lastly, egestion takes place where the undigested food is excreted. The pseudopods or false feet are the cytoplasmic extensions which help the amoeba to engulf food. The amoeba has no mouth or anus, so digestion occurs through the cell surface.

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Nutrition in Amoeba Diagram

What is Pseudopodia?

Pseudopodia or false feet are temporary projections of the cell membrane of a eukaryotic cell. Movement with pseudopodia is the most primitive form of movement that occurs in amoeba. Amoeba, which is a single-celled organism, is characterised by the property of forming arm-like protrusions that have the ability to change their shape constantly. The shape of the amoeba is irregular due to the presence of these pseudopodia.

Interesting Facts

  • Amoeba appears like blobs of jelly-like substance, and it does not have any fixed body shape.

  • Amoeba can create body extensions called pseudopodia which help in digestion and locomotion.

Key Features

  • Amoeba belongs to protozoans, and it is responsible for causing amoebic dysentery.

  • The process of absorbing liquids by amoeba is known as pinocytosis.

  • Contractile vacuoles are accountable for osmoregulation, and this prevents the cell from bursting.

  • The food vacuole is where digestion occurs, as the digestive enzymes are present here.

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FAQs on Feeding and Digestion in Amoeba

1. What are mixotrophs?

Mixotrophs use different sources of carbon and energy for their nutrition. One popular example is Euglena sp., which acts as an autotroph as well as a heterotroph.

2. What is the mode of nutrition in blue-green algae?

Blue-green algae can use different carbon sources and energy sources and can behave as autotrophs, heterotrophs or mixotrophs.

3. What is saprophytic nutrition?

Saprophytic nutrition is the nutrition in which organisms feed on dead and decaying matter. Examples include fungi.


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