Amoeba is the simplest and most primitive protista, which can perform all vital activities such as locomotion, nutrition, digestion etc. in a single cell. Hence, it is regarded as an a cellular animal. It was first discovered by Von Rosel Rosinhof, in 1755. Amoeba means changing in shape.
Systematic Position:
Kingdom- Protista
Phylum – Protzoa
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Sub-Phylum – Sarcomastigophora
Class – Sarcodina/Rhizopoda
Habit and Habitat:
Amoeba proteus lives in fresh water ponds, pools, ditches, streams etc.
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Morphology:
Ameoba is a unicellular microscopic protista. It is transparent and coulerless. Its shape is irregular due to presence of finger like processes called pseudopodia. It becomes spherical when all pseudopodia are withdrawn. The size varies from 0.2mm to 0.5mm in diameter. The cell body is covered by a thin plasma membrane called plasmalemma. This plasmalemma bounds the cytoplasm.
The cytoplasm is differentiated into outer ectoplasm and inner endoplasm. The endoplasm occurs in two colloidal states. The peripheral gel like state is called plasmagel and central flowing state or sol state is called plasmsol. The plasmsol can be changed into plasmagel and vice versa. The endoplasm contains a number of structures such as nucleus, contractile vacuole food vacuole, water vacuole, endoplasmic reticulum, Golgi body, lysosome, ribosome, mitochondria etc. the contractile vacuole is a pulsatile, fluid filled spherical structure bounded by vacuolar membrane.
At regular intervals, it moves to the surface where it contracts and discharges the excess water, salts and waste products to the surrounding water environment. Therefore, it is osmoregulatory in function. The food vacuoles of gastric vacuoles are the sites for intracellular digestion. The pseudopodia are the temporary projections of the cytoplasm that helps in food capture and locomotion. The Amoeba reproduces asexually by binary fission and multiple fission.