Biology 3.1

some topis from B3.1

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  • Biology 3.1
    • Dissolved Substances
      • Osmosis
        • The movement of water through a partially permeable membrane into a solution with low water concentration
          • Partially permeable membrane
            • stops solute molecules getting through because they are too large
            • allows water molecules through
      • Dissolved substances move by
        • Diffusion
          • The mixing of two substances through the natural movement of their particles from a high concentration to a low concentration
        • Active Transport
          • the movement of substances against a concentration gradient; requires energy
    • Osmosis and cells
      • When the concentrations of the solutions inside and outside a cell are different, it causes water to move into or out of the cell by osmosis
      • Osmosis will gradually dilute the more concentrated solution. for example, water moves from the soil into a plants root hair cells by osmosis, along a concentration gradient.
    • Active Transport
      • Substances are sometimes absorbed against a concentration gradient  i.e. in the opposite direction to the normal distribution. This.....
        • requires energy from respiration
        • is known as active transport
      • Active transport allows cells to absorb sugar and ions, which can pass through cell membranes, from very dilute solutions
        • Plants absorb ions from very dilute solutions in the soil by active transport.
        • In humans, sugar can be absorbed from the intestine and from the kidney tubules by active transport
    • Exchanging Materials
      • Many organ systems are specialised for exchanging materials. features that make exchange surfaces efficient include
        • being thin, providing a short diffusion path
        • Being vantilated (in animals) for gas exchange.
        • a large surface area
        • having an efficient blood supply (in animals)
      • The larger and more complex an organism is, the more difficult it is to exchange materials. Exchange surfaces in organisims are adapted to maximise their effectiveness.
        • In humans
          • alveoli increase the surface area of the lungs
          • Villi increase the surface area of the small intestine

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