5. The Fundamental Unit of Life
Cell: It is the smallest unit of life capable of performing all living functions. Milestones in Cell Biology Biologists Major contributions Discovered cell Robert Hooke Discovered microscope Leeuwenhoek Nucleus Robert Brown Coined term protoplasm Purkinje Schleiden and Schwann Presented Cell theory First described Golgi apparatus Camillo Golgi Cell theory All plants and animals are composed of cells The cell is the basic unit of life. This was further expanded by Virchow by suggesting that all cells arise from pre-existing cells. Unicellular organism – It is made up of only a single cell, e.g. Amoeba, Paramecium Multicellular organism – It is made up of many cells, e.g. algae, plants, animals, etc. Structural organization of cell Cell wall – It is the outermost structure present in plant, fungal, and some bacterial cells; it is absent in animal cells Plasma membrane or cell membrane – It is the outermost covering of all cells. It separates the contents of the cell from the external environment. Important functions of cell membrane: Regulates the entry and exit of substances in and out of the cell Performs certain physical activities such as diffusion and osmosis o Diffusion – It is the spontaneous movement of molecules from a region of high concentration to a region of low concentration o Osmosis – It is the movement of water molecules from a region of high concentration to a region of low concentration, through a selectively permeable membrane Cytoplasm – It is the fluid that fills the cell; It contains all cell organelles
Cell organelles Nucleus It controls all the cellular activities of the cell; acts like the brain of a cell. Important components of nucleus are nuclear membrane, nucleoplasm, containing chromatin and nucleolus Prokaryotic cell - The nuclear region is poorly defined; membrane-bound organelles are absent. The undefined nuclear region containing only nucleic acid is...
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