Structure and Life Cycle of Amoeba (Amoeba Labelled Diagram)

Read this article to learn about the Structure and Life Cycle of Amoeba !

Systematic Position

Phylum: Protozoa

Class: Rhizopodea

Order: Amoebida

Genus: Amoeba

Species: proteus

Structure of Amoeba

Amoeba proteus is a single-celled organism that can be found in many ponds, lakes, freshwater pools, and slow-moving streams. It usually moves slowly and feeds on algae, bacteria, and other things. Under a microscope, it looks like a small, irregular mass of hyaline protoplasm that looks like jelly (Figure 1). Amoeba doesn’t have a set shape, and the shape of its body keeps changing as small “fingers” called pseudopodia grow out of it.

Pseudopodia are temporary protrusions that look like fingers and end in blunt, rounded tips. The body is always giving out or taking back these protrusions. Many pseudopodia are made at the same time. The pseudopodia allow the amoeba to move. It also helps to catch food. Like a normal cell, an amoeba’s body is made up of three main parts: the plasma membrane, the cytoplasm, and the nucleus.

(Amoeba Labelled Diagram)

Figure 1: Amoeba Labelled Diagram

i) Plasma lemma

Plasma lemma is an amoeba cell membrane that is very thin, fragile, and stretchy. It is made up of two layers of molecules of lipids and proteins. This membrane lets water, oxygen, and carbon dioxide move in and out of the animal and the environment in a controlled way. On the outside of the plasma lemma, there are small ridge-like projections that help hold the organism to its base.

ii) The cytoplasm

The cytoplasm is differentiated into Ectoplasm and endoplasm. The ectoplasm forms the outer and relatively firm layer lying just beneath the plasma lemma. It is a thin, clear (non­granular) and hyaline layer It is thickened into a hyaline cap at the advancing end at the tips of pseudopodia.

There are a number of clear longitudinal ridges in the ectoplasm. Because the ectoplasm has long, narrow ridges, it is considered of as a supporting layer. The endoplasm is the main body mass, and the ectoplasm is all around it. It is granular heterogeneous fluid. The endoplasm is made up of a stiff plasmagel on the outside and a more fluid plasmasol on the inside.

The granules in the more solid and granular plasmagel don’t move at all. In addition to granules, endoplasm also includes a variety of significant inclusions, including a nucleus, contractile vacuole, food vacuoles, mitochondria, the Golgi apparatus, fat globules, and plate-like or bipyramidal crystals. Organelles and other structures are suspended in endoplasm. The nucleus, contractile vacuole, food vacuoles, and water globules are among these organelles.

iii) Nucleus

Amoeba proteus has a solitary noticeable nucleus. In early specimens, the nucleus appears as a biconcave disc, but in older specimens, it is often folded and twisted. The nucleus has a solid nuclear membrane, also known as the nuclear envelope, and it is made up of a transparent, achromatic material with tiny chromatin grains, also known as chromidia, that are evenly dispersed close to the surface. The nucleoplasm is not in good abundance. Such a nucleus is called massive or granular nucleus.

Life Cycle of Amoeba

In amoebas, reproduction is a cyclical process that happens periodically. Amoeba reproduce mostly asexually, by binary fission, multiple fission, and sporulation.

i) Binary fission

The most typical method of reproduction is this one. The whole organism splits into two daughter amoebae throughout this procedure via mitosis (Figure 2). The division includes the division of the nucleus (karyokinesis), then the cytoplasm (cytokinesis). This occurs when the circumstances are favourable.

Structure and Life Cycle of Amoeba

Figure 2: Binary Fission in Amoeba

ii) Sporulation

Amoebae proliferate when the circumstances are not favourable by internally producing spores. The opening of the nuclear membrane and the release of chromatin building blocks into the cytoplasm are the first two steps (Figure 3). Each block of chromatin gains a nuclear membrane and develops into a little daughter nucleus. Amoebae are created when cytoplasm surrounds the newly produced nucleus.

The peripheral cytoplasmic layer of amoebulae forms a tough and resistant spore-membrane or spore case. About 200 such spores are formed inside a single parent amoeba. Finally the body of parent amoeba disintegrates to release the spores. The spore remains inactive for some time and on getting favourable conditions each spore forms a young amoeba.

Sporulation in Amoeba

Figure 3: Sporulation in Amoeba

iii) Multiple fission

Amoeba splits into much fission under unfavourable circumstances. It pulls back its pseudopodia, swells up, and secretes a three-layered cyst all around it. Its nucleus repeatedly divides during mitosis to produce 500–600 daughter nuclei. Each daughter nucleus splits into tiny amoebae and becomes encircled by a mass of cytoplasm. When favourable circumstances arise, the cyst bursts, releasing the amoebulae, which quickly develop into adult amoebas.

Figure 4A: Multiple fission in Amoeba, Figure 4B: Stages of Multiple fission in Amoeba.