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CBSE - IX
Cell Structure
Cell Structure
Cell wall is the outermost, non-living and rigid layer, seen in a plant cell. Plasma membrane is selectively permeable. Diffusion is spontaneous movement of gases from a region of high concentration to a region of low concentration. Osmosis is diffusion of solvent molecules through a semi-permeable membrane from a region of low concentration to high concentration. If the medium surrounding the cell has a higher water concentration than the cell, called hypotonic solution, the cell gains water by osmosis and swells. If the medium has the same water concentration as the cell called isotonic solution, there is no net movement of water through the membrane and the cell stays the same size. If the medium has a lower concentration of water than the cell called hypertonic solution, the cell loses water by osmosis and then shrinks. Plasmolysis is the shrinking of the cell away from the cell wall. Nucleus is the control centre of the cell.
Cytoplasm is the fluid living content between the plasma membrane and the nucleus. Protoplasm is the nucleus along with the cytoplasm that makes up the living content of the cell. Cytosol is the liquid part of the cytoplasm other than the organelles. Endoplasmic reticulum is the protein synthesizing site of the cell. Ribosomes are small granules that synthesize proteins. Golgi apparatus is the site for storing and transporting proteins across the cytoplasm. Mitochondria is the power house of the cell. Lysosomes are known as suicide bags as these enzymes destroy injured or old organelles and foreign substances like bacteria. Vacuoles are storage units in cells. Chromoplasts are colored plastids and leucoplasts are colorless plastids. Difference between Plant cell and animal cell includes size, vacuole, cell wall and chloroplasts.