Cell : Structure and Function
Call : Structure and Function
The Basic Unit of Lite
Cell is a basic membrane-bound unit that contains the fundamental molecules of life and of which all life begins.
Robert Hooke was the first to observe dead cells in cork and Anton von Leeuwenhoek first saw and described live cells.
Robert Brown later discovered the nucleus in the cells of orchid roots.
Cell theory was jointly put forward by Matthias Schleiden and Theodor Schwann in 1839. Cell theory includes following
All living organisms are composed of one or more cells.
Cells are the basic units of structure and function in living beings.
All cells are produced from previously existing cells.
TYPES OF CELLS
Cells can be mainly classified into two types on the basis of nuclear organisation: cells that have membrane bound nuclei are called eukaryotic and cells that lack a membrane bound nucleus are called prokaryotic.
Cells differ greatly in size, shape and activities. Mycoplasma is the smallest cell (0.15 - 0.3 um in length) while the largest single cell is the egg of ostrich.
- Cell wall is absent in animai cell. A plant cell consists of cell wall and protoplast. Protoplasm includes cytoplasm and
nucleus. Various cell organelles like mitochondria, Golgi bodies, etc., and many cytoplasmic inclusion bodies are found in the cytoplasm.
- In primitive cells of prokaryotes, genetic material is not organised in the form of nucleus and other membrane bound cell organelles are also absent.
- Eukaryotic cells, in general comprise of following main components:
- it is the outer rigid, protective covering of plant cells, fungi and some protists
composed of cellulose microfibrils running through a matrix of other complex polysaccharides.
- Bacterial cell wall is made up of peptidoglycan. Algae have cell wall made up of cellulose, galactans, mannas and minerals like calcium carbonate.
- In other plants, it consists of cellulose, hemicellulose, pectins and proteins. Cell wall can have three parts-
(i) Middle lamella - Cementing layer between the adjacent cells and is the first layer to be formed during cytokinesis. It is made up of calcium and magnesium pectates.
(ii) Primary wall - It is formed inner to middle lamella and is capable of extension. It grows by addition of materials
within the existing wall.
(iii) Secondary wall - It is produced in mature cells that have stopped growth. It is formed by deposition of materials over surface of existing structure.
Plasmodesmata links the cytoplasm of adjacent plant cells in the cell wall.
- Provides mechanical support and protection from mechanical injury.
- Provides shape and rigidity to the cell.
- Counteracts osmotic pressure and prevents bursting of plant cells by inhibiting excessive endosmosis