The cell is the structural and functional unit of living organisms. It was discovered by Robert Hooke in 1665. Cell in Latin means “little room”. Many organisms, such as bacteria, protozoa and yeasts consist of single cell called Unicellular Organisms and complex organisms are known as Multicellular Organisms made up of many cells.
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Structure of Cell
All cells have three major functional regions:
1. Cell membrane or plasma membrane and cell wall
2. The nucleus and
3. The cytoplasm
The outer boundary of cell is plasma membrane. Inside it lies the cytoplasm. Various cellular or cell organelles and inclusions like mitochondria, chloroplasts etc. are suspended in the cytoplasm.
|1. They are found in multicellular organisms.
2. They are large sized.
3. They may be external or internal to the body of an organism.
4. The organs are formed of tissues, tissues comprise of cells and cells are formed of organelles.
5. Organs coordinate to form organ system, while organ system forms the body of an organism.
|1. They are found in all Eukaryotic cells.
2. They are very small sized.
3. They are mostly internal.
4. It is made up of micro and macro molecules.
5. Organelles coordinate to produce the cell.
Plasma membrane permits the entry and exit of some materials in the cells. Therefore, plasma membrane is known as selective permeable membrane.
(i) Diffusion: The spontaneous movement of molecules from a region of high concentration to one of lower concentration, until uniform concentration is finally achieved. It is faster in the gaseous phase than in liquids and solids.
(j) Osmosis: The passage of water from a region of high water concentration through a semi-permeable membrane to a region of lower water concentration.
(k) Endocytosis: The ingestion of material by the cells through the plasma membrane.
(l) Exocytosis: In this process the membrane of a vesicle can fuse with the plasma membrane and extrude its contents to the surrounding medium. This is also known as cell vomiting.