1898 Golgi apparatus seen and described for the first time by Camillo Golgi by using staining technique 1932 Electron microscope was invented by Knoll and Ruska.

Later, electron microscope was developed with a resolving power of 0.004 nm. It provides direct information about structures of cell components ranging in size from 0.4 to 200 nm.

This chapter proposes to examine the structure of plant and animal cells and understand their functions. There is no single ideal cell that can accurately match to the features of about four million species of living organisms.

What is learnt from one kind of cell can be applied, sometimes, directly, sometimes, with modifications, to other kind of cells. However, unequivocally, there are two general types of cells: the prokaryotic [bacteria and cyan bacteria (blue green algae)] and eukaryotic, found in all other organisms. The representative types of both types of cells are presented in the Table


Prokaryotes and Eukaryotes

The living world can be divided into five Kingdoms according to a recent classification. But on the basis of the cell structure, they are of two types: prokaryotes and eukaryotes.

The prokaryotic cell is the simplest kind ever known and as per the fossil evidences, it probably came into existence nearly 3 to 3.5 billion years ago. These cells are very small in dimension (0.1 to .25 porn) among these are the mycoplasmas, the smallest cells ever known;

Bacteria and cyan bacteria (blue-green algae) the living portion of the prokaryotes isle externally by a plasma membrane. A more or less rigid cell wall and jelly like mucilage capsule or sheath cover it.


The bacterial cell wall contains lipids, carbohydrate muccopolysaccharides derived from amino acids and amino sugars the cyan bacteria however, and structurally more complex than those of bacterial cells.

The cellular content of prokaryotes consists of an outer, less electron dense area inner, very dense cytoplasm, where the nuclear mass is seen. Thin tangled fibers, about 31(in diameter are present in the nuclear area.

They are the strands of deoxyribonucleic acid (1 the nuclear area, characteristically, lacks the nuclear membrane. Hence, the space occupy the single circular DNA (the so-called chromosome) is called the nucleoid and is pre direct contact with the rest of the protoplasm.

The cyan bacteria and some bacteria pi layered membranes that are involved in photosynthesis. These have been derived from the plasma membrane the photosynthetic pigment in bacteria isbacteriochlorophyll cyan bacteria, chlorophylla andphycocyanin.


The only cell organelle present in the prokaryotes is the ribosome. These are rounded structures, about 15 to 20 nm in diameter. All other organelles, typical of a euk; cell, are absent in prokaryotes. Some possesses flagella but the fine structure of the flag is completely different from that of aeukaryote.

The bacteria divide by simple fission. The DNA remains attached to a mesoso structural feature of the plasma membrane. Division of the embosomed into two halves prey the bacteria] cell division. This, later, forms the nuclear area of the daughter cells.

Bacteria and cyan bacteria (show similarity in their alibi form the resting spores. A spore coat is formed around the nuclear area and a small ammonia cytoplasm and the cell can remain suspended in this condition until it germinates. The BAC can withstand a temperature of untold 20°C, where as cyan bacteria remain alive up to 7

The eukaryotic cell is far more elaborate in structure than the prokaryotic one 2.1 d). An internal division of labour has taken place in it.


The eukaryotic cell is surrounded plasma membrane. In the case of the plant cells, this membrane has an outer cell wall, air living component made up of cellulose. The hereditary material is enclosed in a membrane bow nucleus and is segmented into complex nucleoprotein bodies, called chromosomes.

The nun of chromosomes is characteristic of a species. The organelles present in the cell carry out van functions. For example, the mitochondria convert chemical energy of carbohydrates, and fats into utilizable form of ATP and endoplasmic reticulum and Golgi apparatus are concerned with the synthesis and packaging of the macromolecules needed for cellular structure and function.

The sun light is trapped by green plants in membrane bound chloroplasts and is converted into chemical energy of carbohydrates. The vacuoles, lysosomes, peroxisomes and glyoxisomes, all membrane enclosed organelles, play definite roles in the eukaryotic cells. The ribosomes, chromosomes and cytoskeletal structures like microtubules and microfilaments are not membrane-enclosed structures. Summarizes the structures and functions of sub-cellular components, present in a eukaryotic cell.

A comparative account of prokaryotes and eukaryotes is given in the comparative relative sizes of two types of cells is presented in the