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OCR Biology B3 part 2

OCR Biology B3 part 2



revision part 2 for ocr biology b3

revision part 2 for ocr biology b3



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    OCR Biology B3 part 2 OCR Biology B3 part 2 Presentation Transcript

    • Revision lesson 2
    • Enzymes
      • Enzymes are biological catalysts – they speed up a biological reaction.
      • Each enzyme is specific to a substrate. The substrate molecules are changed into product molecules.
      • Enzyme controlled reactions are affected by pH and temperature.
      • Optimum pH or temperature – the pH / temperature where the reaction works best.
      • Lock and key theory- each enzyme has a unique sequence of amino acids – therefore each enzyme has a different shape. Within this shape is a structure called an active site. Only one type of substrate can fit into the active site, this makes enzymes specific to a reaction. Once the substrate is attached to the active site it is turned into a product. The enzyme is like a lock and the substrate is like the key.
    • Definitions
      • Optimum – the best temperature and pH that enzymes work at.
      • Denatured – when the shape of the enzyme’s active site is changed irreversibly
      • Substrate – the chemical that is reacting
      • Active site – the area on the enzyme that the substrate fits into.
    • Denaturing enzymes
      • If the shape of an enzyme changes it can no longer catalyse a reaction because the substrate can no longer fit into the active site. The enzyme has become denatured.
      • Enzymes can be denatured by:
      • Extremes of pH
      • High temperatures
    • Diffusion
      • Diffusion – the movement of a substance from a region of high concentration to a region of low concentration.
      • Moving substances in the body
      • Different substances diffuse in and out of the cells across the cell membranes.
      • Oxygen – moves from the lungs into the red blood cells. It then moves from the red blood cells into the body tissue.
      • Carbon dioxide – moves from the body tissue into the blood, then from the blood into the lungs.
      • After eating – digested food molecules move from the small intestine into the blood. They then leave the blood and go into body tissue
    • Surfaces Across Which Gases Are Exchanged Are Often Specialised in Humans by Having Large Surface Areas This is to increase the rate at which diffusion can occur
      • Good examples in the Human Body are:-
        • Alveoli
        • Villi
        • Placenta
        • Neurones
    • Diffusion Cells use diffusion to swap the oxygen they need for the carbon dioxide they no longer want: Other examples of where diffusion happens in humans: Alveoli in the lungs Villi in the intestines Oxygen diffuses in Out goes waste CO 2
    • Changing the rate of diffusion
      • It can be increased by:
      • Increasing the surface area
      • Decreasing the diffusion distance
      • A greater concentration difference
    • Surfaces adapted for diffusion Villi
      • Diffusion takes place in the villi in the small intestine and the alveoli in the lungs. Both are adapted to increase the rate of diffusion.
      • Villus – produce a large surface area, villi wall have folds (microvilli). Surface area of small intestine is approx 9 m 2 .
      • One cell thick, food does not have to far to diffuse into the blood
      • Good blood supply – means digested food is quickly taken away from villus so more can diffuse across to replace it
      • Membrane of villi is permeable, this means food molecules can pass through the membrane
    • Alveoli – in the lungs
      • Breathing makes sure there is always a high concentration of oxygen in the alveoli.
      • Good blood supply makes sure as oxygen diffuses into the blood it is replaced with blood containing very little oxygen.
      • Alveolus is only one cell thick so the gases do not have far to travel
      • Large numbers of alveoli – this helps to increase the surface area, so more molecules can move across at any time.
      • Alveoli membrane is permeable to gases and is also moist; this helps to speed up diffusion.
    • Other substances adapted for diffusion
      • Placenta
      • To move substances across the placenta as quickly as possible. To speed up movement, the placenta has:
      • A very large surface area
      • A very thin wall so substances only have a short distance to diffuse
      • The leaf
      • To increase the rate of gas exchange, the leaf has a large surface area. The under-surface of the leaf also has many stomata through which gases can diffuse.
      • Synapses
      • The gap between two neurones (nerve cells). The synapse releases a chemical that can diffuse across the gap between the two neurones. A large surface area and short diffusion distance is important.
    • The Alveoli in the Lungs Provide a Massive Surface Area for Exchange of Oxygen & Carbon Dioxide Alveoli