Biology Chapter 1 - Part 2

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  • Biology Chapter 1 - Part 2
    • Osmosis
      • Movement of water across a partially permeable membrane from high water conc. to low water conc.
      • 2 solutions have same conc. = isotonic  Water with high conc. = hypertonic Water with low conc. = hypotonic
      • When plant cells are placed in a hypertonic solution a lot of the water leaves the cell, the vacuole and cytoplasm shrink and the membrane pulls away from the cell wall (plasmolysed)
      • Osmosis is important to maintain turgor (turgid shape)  in plant cells
    • Active transport
      • Cells use active transport to absorb substances in short supply across a partially permeable membrane against the conc. gradient
      • Active transport requires the energy released during respiration
      • Examples of active transport: -Root cells absorb mineral ions from dilute solutions in the soil -glucose can be reabsorbed in the kidney tubules
    • Exchanging materials
      • Large organisms have many cells that are not in contact with their  environment, so have  special exchange surfaces to obtain the food and water they need
      • Efficient exchange surfaces have: large surface area, thin walls, short diffusion path and efficient transport system ie. blood stream
      • Plants have long thin roots and root hair cells increase surface area
        • Leaves are flat and thin with internal air spaces and stomata to allow gases in and out of the leaves
    • Exchange in the gut
      • The villi line the inner surface of the small intestine and are the exchange surface for food molecules.
        • Villi increase the surface area od small intestine
        • The walls of the villi are very thin and there are many capillaries close to the wall
        • The villi use both diffusion and active transport to absorb the product of digestion

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