Amoeba: Structure and Life Processes

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Structure of Amoeba, Nutrition in Amoeba, Reproduction in Amoeba

Amoeba is one of the well-known members of Kingdom Protista. This post will provide you with everything you need to know about the structure as well as the life processes of Amoeba.


Kingdom Protista is made up of species that are mostly single-celled with only a few being multicellular.

Unlike bacteria which are prokaryotes, members of this Kingdom are eukaryotes. This means that they have a nucleus enclosed within a nuclear envelope.

Amoeba is a unicellular protist mostly found in stagnant or slow-moving freshwater and saltwater.

Structure of Amoeba

Amoeba has an irregular shape and its structure consists of 3 main parts; cell membrane or plasmalemma, cytoplasm, and nucleus.

The cell membrane is the body covering and it is selectively permeable to water and dissolved gases.

The cytoplasm is made up of an outer ectoplasm and an inner endoplasm. The endoplasm has a less fluid outer plasmagel and a more fluid inner plasmasol.

The nucleus controls the life activities of the cell. It is located in the endoplasm of the cytoplasm together with other organelles such as contractile vacuole and food vacuole.

Amoeba forms extensions or false feet called pseudopodia or pseudopods.

Amoeba, Structure of Amoeba

Amoeba like any other living thing also undergoes or performs some life processes.

These life processes include movement, reproduction and growth, nutrition, excretion and osmoregulation, respiration, and response to environmental changes.


The cell moves using the most primitive form of animal locomotion known as an amoeboid movement. This is by the use of false feet or pseudopodia.

A bulge first forms at a portion of the cell membrane which extends into a long pseudopodium. The cytoplasm flows into the pseudopodium drawing the posterior part of the cell with it.

A moving or locomotive Amoeba has two parts, a hyaline cap, and an uroid. The hyaline cap is the anterior part while the uroid forms the posterior part.

Reproduction in Amoeba

Reproduction in Amoeba is asexual. It occurs both under favorable and unfavorable conditions. Under favorable conditions, reproduction is by binary fission while it is by multiple fission or sporulation under unfavorable conditions.

Binary Fission

Binary fission in Amoeba is irregular. During this type of reproduction, a fully-grown cell stops moving and goes through karyokinesis and cytokinesis.

The cell first goes through karyokinesis which is the division of the nucleus during mitosis.

Cytokinesis which is the division of cytoplasm follows after the nuclear division to produce two daughter Amoeba cells that grow into matured cells.

Multiple Fission

This type of reproduction occurs by encystment. A fully-grown cell stops moving and forms a cyst around it.

The encysted cell then goes through cell divisions and produces many spores. When conditions become favorable, the cyst wall bursts to release the daughter amoebas or amoebae that grow into matured cells.

Amoeba, Reproduction in Amoeba, Binary fission, Multiple fission

Nutrition in Amoeba

Feeding is by phagocytosis. The cell feeds by engulfing food particles such as small algae and bacteria.

This is a holozoic mode of nutrition as the food is ingested and processed internally to obtain energy.

Amoeba uses its pseudopodia to engulf food particles to form a food vacuole inside it. Enzymatic digestion occurs inside the food vacuole and the nutrients diffuse into the cytoplasm.

The wastes are then expelled from the cell.

Amoeba, Nutrition in Amoeba

Excretion and Osmoregulation

Amoeba excretes mainly ammonia and carbon dioxide. These diffuse to the external environment through the cell membrane.

Osmoregulation is by the action of the contractile vacuole. The contractile vacuole collects and expels excess water to maintain the water and ionic balance of the cell.

The water expelled also contains traces of metabolic wastes.


The cell exchanges dissolved gases with the environment through the cell membrane by diffusion. Oxygen diffuses in while carbon dioxide diffuses out.


Although Amoeba has no sense organs to perceive stimuli, it is highly sensitive to changes in its environment.

It moves in the opposite direction when it encounters an obstacle. It moves away from salt, sugar, acid, and alkali concentrations to which it is not accustomed.

During harsh environmental conditions, Amoeba forms a cyst in response to the conditions.


Amoeba is a single-celled protist having no fixed shape. It moves using the most primitive form of animal locomotion known as an amoeboid movement.

It reproduces asexually by binary fission or multiple fission depending on the condition of its environment.

Amoeba also performs other life activities such as feeding, exchange of gases, removal of waste products, and more.

Amoeba/Protist Notes & Assessment

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