Vacuoles are large in size in plant cells and small in size in animal cells. Vacuoles are blank looking structures in the cytoplasm. It has a membrane callednuclear membrane.It has a smaller spherical body callednucleolusand thread like structures calledchromosomes.The chromosomes carrygeneswhich transfer characters from the parents to the off springs. The nucleusis a spherical body generally found in the centre of the cell. It contains other components (organells) like mitochondria, golgi bodies, ribosomes, vacuoles etc. The cytoplasmis a jelly like substance between the cell membrane ad nucleus. In plant cells the cell membrane is covered by another thick covering calledcell wall. The cell membranegives shape to the cell, protects the inner parts of the cell and allows movement of materials in and out of the cell. Human cheek cells as seen under a microscopeĥ) Parts of a cell :- The main parts of a cell are cell membrane (plasma membrane), cytoplasm and nucleus. Onion peel cells as seen under a microscope The largest cell is the egg of an ostrich (17cm x 13cm). The smallest cell is the cell of bacteria (0.1 to 0.5 micrometre). They may be as small as millionth of a meter (micrometre or micron) or large as a few centimetres. Some cells are spherical, round, elongated, spindle shaped, or branched.Ĥ) Size of cells Cells in living organisms are of different sizes. Eg : amoeba, white blood cells in human beings. Organisms made up of only one cell are calledunicellularorganisms.Eg: amoeba, paramaecium.ģ) Shape of cells Cells are of different shapes.

Organisms made up of many cells are calledmulticellularorganisms.Eg: a tree, an elephant. The number of cells in a tall tree or an animal like an elephant or human being are billions and trillions of cells. Some organisms are made up of a single cell and some are made up of many cells. The cells which Hooke observed were actually dead cells of plants.Ģ) The Cell Cellsare the basic structural units of living organisms. The boxes were separated from each other by a wall or partition. He noticed small boxes or compartments in the cork slice. CHAPTER - 8CELL – STRUCTURE AND FUNCTIONSġ) Discovery of the cell In 1965 Robert Hooke observed slices of cork from the bark of a tree under a simple magnifying glass.

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