Exam (elaborations) Biology Notes(The Fundamental Unit980

all living organism are made up of cells and functional unit as it is the smallest structure capable of performing basic life processes. Two postulates of the cell theory are1. All organisms are made up of cells. 2. All cells exist from pre- existing cells. B) Who discovered cell-It was discovered by Robert Hooke in 1665.Other discoveries about cell are: a) Robert Brown –Nucleus of the cell in 1831 b) Anton Van Leeuwenhoek – Free living cells in pond water (bacteria) in 1674 c) Purkinje – Fluid substance of cell (Protoplasm) in 1839 d) J.E.Virchow- Expanded cell theory (all cells arise from pre-existing cells) in 1855 e) M.J. Schleiden and T. Schwann – Gave cell theory (cell is basic unit of life) in 1838-39 f) The discovery of electron microscope in 1940 helped to understand complex structure of cell and its organelles. C) What are cell organelles- Each cell has got certain basic components within it known as cell organelles. Each kind of cell organelle performs a special function that is why a cell is able to live and perform all its function in any organism. These organelles are suspended in the cytoplasm. D) Basic components of cell- Plasma membrane, Nucleus and cytoplasm. E) PLASMA MEMBRANE: a) It is the outermost layer of animal cell. b) It gives shape to the cell and provides mechanical support and protection to the inner contents of the cell. c) It is protective covering of the cell. d) It is called selectively permeable membrane as it allows the entry and exit of some materials in and out of the cell. e) It is highly flexible, living membrane made up of organic molecules- proteins and lipids. F) What is difference between diffusion and osmosis- 2 DIFFUSION OSMOSIS 1. The process of movement of molecules from a region of higher concentration to lower concentration to spread uniformly in given space. 1. The process of movement of water molecules from region of higher concentration to lower concentration through semipermeable membrane. 2. It is seen in solids, liquids and gases. 2. It is seen only in liquids. 3. It helps in exchange of gases like CO2 and O2 between cell as well as its external environment. 3. It helps in absorption of water by plant cells and unicellular organisms. 4. 4. G) What happens when we put an animal cell into a solution of salt or sugar? ** Solute + Solvent ---------- SOLUTION Three things can happena) Higher water concentration than a cell in surrounding medium i.e. the solution is diluteforms hypotonic solution-Cell gains water and swells up (becomes turgid)-process is Endosmosis. b) Lower concentration of water than a cell in surrounding medium i.e. the solution is concentrated-forms Hypertonic solution- Cell loses water and shrinks (plasmolysed i.e. becomes flaccid)-process is Exosmosis. c) Same concentration inside and outside the cell-forms Isotonic solution- No change and remains normal cell. Conclusion: Osmosis is special kind of diffusion through plasma membrane which can be affected by the amount of substance dissolved in water. 3 H) What is Plasmolysis- When living plant cell loses water through osmosis, there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is called as PLASMOLYSIS. I) What is Endocytosis – It is the process which enables the cell to engulf in food and other material from its external environment. It takes place as cell membrane is highly flexible. Example – Unicellular organism Amoeba acquires its food through this process.