NCERT Chapter Summary: Cells

The fundamental organisational unit of life is the cell. Cells are enclosed by a plasma membrane composed of lipids and proteins. The cell membrane is an active part of the cell. It regulates the movement of materials between the ordered interior of the cell and the outer environment.

In plant cells, a cell wall composed mainly of cellulose is located outside the cell membrane. The presence of the cell wall enables the cells of plants, fungi and bacteria to exist in hypotonic media without bursting.

The nucleus in eukaryotes is separated from the cytoplasm by double-layered membrane and it directs the life processes of the cell. The ER functions both as a passageway for intracellular transport and as a manufacturing surface.

The Golgi apparatus consists of stacks of membrane-bound vesicles that function in the storage, modification and packaging of substances manufactured in the cell.

Most plant cells have large membranous organelles called plastids, which are of two types - chromoplasts and leucoplasts. Chromoplasts that contain chlorophyll are called chloroplasts and they perform photosynthesis. The primary function of leucoplasts is storage.

Most mature plant cells have a large central vacuole that helps to maintain the turgidity of the cell and stores important substances including wastes.

Prokaryotic cells have no membrane-bound organelles, their chromosomes are composed of only nucleic acid, and they have only very small ribosomes as organelles. 

Cells in organisms divide for growth of body, for replacing dead cells, and for forming gametes for reproduction.