This blog post provides readers with the following objectives. The reader will be able to:

·             Describe the structure of Amoeba

·             Explain the life processes of Amoeba

Amoeba Definition and meaning

Kingdom of Amoeba: Protoctista

Phylum: Rhizopoda

Habitat of Amoeba

Amoeba can be found in ponds, ditches, shallow muddy and in damp soils.

Structure of Amoeba

Amoeba is a unicellular organism. The body consists of protoplasm made up of the nucleus and the cytoplasm. The cytoplasm is made up of outer clear layer, called ectoplasm  oplasmagel and more fluid, dense inner layer called endoplasm or plasmasol.

The endoplasm contains food vacuoles, contractile vacuoles and a dense nucleus. A food vacuole consists of partly digested food particles surrounded by bubbles of water.

A ‘false feet’ or pseudopodia projects from the body surface. Amoeba does not have constant shape. Its shape keeps changing by the formation of pseudopodia. It has a jelly-like body with no definite shape surrounded by a thin semi permeable membrane.

Diagram of Amoeba

structure of Amoeba proteus

Life Processes of Amoeba

Nutrition in Amoeba

What's the food for Amoeba?

Amoeba feeds on smaller organisms like bacteria, plankton and diatoms. It obtains its food through phagocytosis. It engulfs the food together with water with its pseudopodia to form food vacuole.

Enzymes are released from the cytoplasm into the food vacuole to digest the food. The soluble end product diffuses into the cytoplasm. The unwanted waste is released through the cell membrane by a process called exocytosis.

diagram of Amoeba engulfing prey with labels

Irritability in Amoeba

Amoeba responds to environmental conditions. Response to the stimuli is called taxis (towards a weak light but avoids powerful ray of light. Amoeba avoids adverse conditions for example, insufficient food, water or pond drying. The body is rounded, and it goes into a resting state called a movement). Amoeba reacts to light, temperature, various substances, and other irritants. It moves to cyst.

Excretion in Amoeba

Waste products of metabolism in Amoeba include carbon dioxide, urea and ammonia. These waste products diffuse out through the cell membrane. Others are dissolved in water in contractile vacuole and they are eliminated together with excess water.

Respiration in Amoeba

Amoeba has no special structures for respiration. Gaseous exchange in amoeba is simply through the process of diffusion. It obtains oxygen for respiration from the surrounding water by diffusion through the cell membrane. Carbon dioxide produced from respiration diffuses out into the surrounding water.

Movement in Amoeba

Amoeba moves by using pseudopodia or "false feet". It moves by controlling the flow of its cytoplasm forming extensions or projections called pseudopodia (singular: pseudopodium). The pseudopodia grow in the direction that the Amoeba will like to move and at the same time withdraw pseudopodia elsewhere.


Osmoregulation in Amoeba

The cell membrane is semi permeable and water continually diffuses into the cell by osmosis. The contractile vacuole removes the water which diffuses into the organism. The contractile vacuole quickly contracts expelling the liquid in it into the surrounding water. The cycle is repeated and this process regulates the amount of water present in the cytoplasm.  


Importance of osmoregulation

1. Osmoregulation enables Amoeba to maintain osmotic balance.

2. It also prevents Amoeba from bursting.

Reproduction in Amoeba

Binary Fission:

Amoeba reproduces asexually by binary fission. The process takes place in favorable condition. Amoeba stops moving and rounds off. The nucleus first constricts and divides followed by division of the cytoplasm. The daughter amoebae separate into two identical cells. 

Reproduction in Amoeba

Multiple Fission or Sporulation

The process takes place in unfavorable condition, such as insufficient food, oxygen, water or temperature. Amoeba secretes a hard resistant cyst around itself. This process is term as encystment. This cyst helps the organism to survive adverse conditions.
Within the cyst the nucleus divides into many parts followed by division of the cytoplasm to form large numbers of amoebae. When conditions become favorable, the cyst break open and numerous amoebae come out in water.

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