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Wednesday, 28 November 2018

Cells and Osmosis





A living cell is bound by a plasma membrane. This membrane is selectively permeable a d allows water and certain molecules and ions to pads through it. As a result, the plasma membrane regulated the movement of materials between the cell and its environment. In contrast, a semi Permeable membrane only allows water molecules to pass through it.

Osmosis in animals cells 

Animal cell contain mainly cytoplasm and cell organelles. In higher animals, the cells are bathed in intercellular fluid or plasma. The concentration of the solute in these fluids is Important for the wellbeing and functioning of the cells.

    A living cell may find itself in any one of the following situations:

• the fluid surrounding the cell is more concentrated than the inside of the cell. In this case, the surrounding fluid is said to be hypertonic to the contents of the cell. There is a net movement of water molecules out of the cell into the surrounding. This is known as exosmosis. It causes the cell to shrink.

• the fluid surrounding the cell is less concentrated than the inside of the cell. Here, the surrounding fluid is said to be hypertonic to the contents of the cell. There is s net movement of water molecules from the surrounding fluid into the cell. This is known as endosmosis. It causes the cell to swell, and eventually rupture.

• the surrounding fluid and the cell contents have the same concentration. Hence, they ate said to be isotonic. There is no net movement of water molecules in or out of the cell.

    To survive the function well, the living cell and the fluid that bathes it must be isotonic or be able to maintain an osmotic balance. Endosmosis and exosmosis can leaf to the eventual death of an animal.

Osmosis in plant cells

Plant cells have cell membranes and cells walls. The cell wall is a tough and fairly elastic structure that is freely permeable to all molecules and ions. The cell membrane, however , is selective permeable unlike an animal, most of the space in plant cell is occupied by a large central vacuole that contains cell sap. Cell slap is a complex mixture of solutes. It had s high concentration and tends to draw in water into the cell from the surroundings by osmosis.

      When endosmosis occurs, Water flows into the vacuole of s plant cell, causing the cell to swell. The cell, however, does not rupture because, although the cell wall stretches to s certain extent, it is tough and does not break. It  also prevents the cell membranes from expanding. A high pressure builds up inside the cell and makes it turgid.

    When exosmosis occurs, Water flows out of the vacuoles of the plant cell Into the surroundings. As a result, the vacuole shrinks and eventually pulls the cytoplasm from the cell wall. This process is known as plasmolysis.

   Turgidity is important in land plants. It makes the plant firm and gives  support , especially to herbaceous plants. If plant cells are not turgid. The plant will wilt. The plant will easily recover if it is supplied with water. However, if water is not supplied, the ant will die when all it's cell becomes plasmolysed.

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