Biology B2 GCSE

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  • Biology B2 Revision
    • Transport in cells
      • Diffusion
        • Diffusion = Spreading out the particles of gas or any solution.
        • It is the movement from an area of HIGH concentration to LOW concentration
        • Diffusion takes place because of the random movement of particles (Ion and molecules)
        • When certain particles move around they bump into each other which causes the movement to be transferred.
        • If the concentrations are different then diffusion takes place much quicker, this is because the low concentration particles attract many moving particles
        • If the concentrations quite similar then the diffusion will take longer to be carried out. This is because the number of particles moving in the low area is more than the particles leaving the area.
        • Net Movement = Particles moving in - Particles moving out
        • The greater different in concentration the faster the diffusion happens.
          • Substances that are dissolved move in and out of living cells through diffusion
            • These are substances such as simple sugars, oxygen and carbon dioxide.
            • Oxygen thats needed for respiration passes through the air in your lungs, the oxygen moves down the concentration gradient from a high region to low.
            • Some cells adapt to make the diffusion process easier and quicker. The most common adaption is increased surface area of the cell membrane. Increases the surface area increased the rate of reaction.
        • If there is a difference between the concentrations this is called the concentration gradient, The bigger the difference the steeper the gradient.
        • Another factor that affects the rate of diffusion is temperature, if temperature increases the particles move around more quickly meaning quicker rate of reaction.
      • Osmosis
        • Membranes that only let some types of particles in are called Partially  Permeable Membranes
          • Partially Permeable Membranes let water move through
        • Dilute sugar = sugar that contains high concentration of water with a low concentration of sugar
          • ConcentratedSugar = A sugar solution that is low concentration with water and high concentration of sugar.
        • Cytoplasm o the cell is made of chemicals dissolved in water, this gives a good concentration of salt and sugar solutions. Water moves from the dilute solution to the concentrated solution across the membrane.
        • A type of diffusion is where water moves across partially permeable membrane from a dilute to a concentrated solution is called osmosis
          • Inside your body the concentration each solute needs to stay the same level for them to work properly.
            • The concentrations of the solutions outside your cells can be different to the concentration inside. the gradient can cause the water to move  into or out of the cells by osmosis.
          • Hypertonic = if the concentration outside the cell is higher than the internal concentration
          • Isotonic = The concentrationthe solutes outside the cell is the same as the internal concentration
          • Hypotonic = If the concentration outside the cell is lower than the internal concentration
        • During a reaction if the water is used up the cytoplasm becomes very concentrated,the fluid that surrounds it becomes hypotonic to the cell and more water moves in by osmosis.
          • If this  becomes too dilute this surrounding fluid becomes hypertonic to the cell and leaves it through osmosis. Osmosis restores the balance.
      • Active Transport
        • Substances move through diffusion and down the concentration gradient, although sometimes these have to be moved against a concentration gradient across a permeable membrane, this is a process called alive transport.
        • Active Transport allows cells to move substances from an area of low to high concentration.This movement is against the concentration gradient.
          • This allows  cells to absorb ions from the dilute solutions.
        • Active transport is widely used in   cells, this is more important in certain situations. For example, mineral ions in soil such as nitrate are found in very dilute situations. These are more dilute than the solution within root hair cells. By using active transport these ions can travel against the concentrationgradient
        • Glucose and other sugars are absorbed through the gut and kidneys into the blood, this is done against a large concentrationgradient

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