Biology, asked by Dilkhushpreetkaur, 11 months ago

flow chart of cell organelles ​

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Answered by kpushpendra693
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Answered by rsultana331
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Answer:

Cell Organelle: Type # 1. Nucleus:

The nucleus was first discovered by Robert Brown in 1833. Since nucleus contains chromosomes and genes, it is called as controlling centre of the cell. There is, usually, a single nucleus per cell, but multinucleate condition is also observed in some protozoa and fungi which results due to repeated nuclear division without division of cytoplasm.

The nucleus is, usually, of spherical or oval shape. However, flattened, irregular, branched and lanceolate shapes are also found in some cells. The nucleus is generally larger in the active cells than in resting cells. The nucleus, usually, occupies a central position, but it occupies peripheral position in some cells. A nucleus consists of three main parts, viz., nuclear envelope, nucleolus and chromatin (Fig. 2.1).

Cell Organelle: Type # 2. Plastids:

Plastids are self-replicating cytoplasmic organelles found in plant cells. Plastids are absent in bacteria, certain fungi and animals. Plastids are of three types, viz., leucoplast, chromoplast and chloroplast. Leucoplasts are colourless and are associated with storage of starch, protein and fat.

Cell Organelle: Type # 3. Mitochondria:

Mitochondrion is a rod-like cytoplasmic organelle which is the main site of cellular respiration. They are sources of energy and are often called as the power house of the cell. They have average length of 3-4 µ and diameter of 0.5-1 µ. Under light microscope, they appear as rod shaped, filamentous or granular structures in majority of the cells.

Their average number varies from 200- 800 per cell. In some protozoa, the number has been recorded up to 500,000 per cell. Mitochondria, contain about 65-70 per cent proteins, 25-30 per cent lipids, 1 per cent RNA and less than 1 per cent DNA.

Mitochondria consists of three main parts, viz:

(1) Membrane,

(2) Christae, and

(3) Matrix (Fig. 2.4).

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Cell Organelle: Type # 5. Ribosomes:

Ribosomes are small cellular particles which are the sites of protein synthesis. Since they are rich in RNA contents, they are called ribosomes. They contain 40-60 per cent RNA and several kinds of protein. The position of ribosomes changes with the stage of cell.

In the young dividing cells, they are usually free in the cytoplasm, while in the mature cells, they are attached with ER. The portion where ribosomes are attached to ER becomes rough.

Ribosomes have two sub-units, viz., larger sub-unit and smaller subunit. The size or weight of ribosome molecule is expressed in S units on the basis of sedimentation rate. The complete unit, larger sub-unit and smaller subunit differ in lower and higher organisms (Table 2.1). Sometimes, ribosomes are observed in cluster. They are called poly-ribosomes. Such ribosomes play an active role in protein synthesis.

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