Class IX: Biology
Chapter 5: The fundamental unit of life.
1) In 1665, Robert Hooke first discovered and named the cells. 2) Cell is the structural and functional unit of all living organisms. 3) Organisms may be unicellular or multicellular. A single cell constitutes the unicellular organism whereas many cells coordinately function in case of multicellular organism. 4) The size, shape and volume of the cell are related to the specific function that they perform. 5) A cell generally shows plasma membrane, nucleus and cytoplasm 6) Plasma membrane is a thin, selectively permeable membrane, covering the cell and is made up of lipids and proteins. 7) Functions of plasma membrane :
i) It separates the contents of a cell from its outside environment. ii) It regulates the flow of substances to and from the cell through diffusion, facilitated diffusion, active transport and endocytosis. 8) Osmosis is diffusion of water through a selectively permeable membrane. 9) A cell placed in different solutions:
i. hypotonic solution : A cell placed in it will gain water. ii. hypertonic solution: A cell placed in it will lose water: Also known as plasmolysis. iii. isotonic solution: A cell placed in it will neither gain nor lose water 10) Cells of Plants, fungi & bacteria: Contain both plasma membrane & cell wall. Cell wall is rigid, non-living & outer most covering, composed mainly of cellulose. 11) When placed in hypertonic solution, a living plant cell shows plasmolysis 12) Cell wall provides mechanical strength to the cell. It permits the cell to withstand huge changes in the surrounding medium. 13) Nucleus is an important, spherical, usually centrally located constituent of the cell and is bounded by double layered nuclear envelope. 14) The nucleus of a dividing cell shows rod-shaped chromosomes, made up of DNA and proteins. In a non-dividing cell, the chromosomes elongate and take the form of thread-like...
Please join StudyMode to read the full document