OCR Biology B3 part 2

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revision part 2 for ocr biology b3

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OCR Biology B3 part 2

  1. 1. Revision lesson 2
  2. 2. Enzymes <ul><li>Enzymes are biological catalysts – they speed up a biological reaction. </li></ul><ul><li>Each enzyme is specific to a substrate. The substrate molecules are changed into product molecules. </li></ul><ul><li>Enzyme controlled reactions are affected by pH and temperature. </li></ul>
  3. 4. <ul><li>Optimum pH or temperature – the pH / temperature where the reaction works best. </li></ul><ul><li>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. </li></ul>
  4. 5. Definitions <ul><li>Optimum – the best temperature and pH that enzymes work at. </li></ul><ul><li>Denatured – when the shape of the enzyme’s active site is changed irreversibly </li></ul><ul><li>Substrate – the chemical that is reacting </li></ul><ul><li>Active site – the area on the enzyme that the substrate fits into. </li></ul>
  5. 6. Denaturing enzymes <ul><li>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. </li></ul><ul><li>Enzymes can be denatured by: </li></ul><ul><li>Extremes of pH </li></ul><ul><li>High temperatures </li></ul>
  6. 8. Diffusion <ul><li>Diffusion – the movement of a substance from a region of high concentration to a region of low concentration. </li></ul><ul><li>Moving substances in the body </li></ul><ul><li>Different substances diffuse in and out of the cells across the cell membranes. </li></ul><ul><li>Oxygen – moves from the lungs into the red blood cells. It then moves from the red blood cells into the body tissue. </li></ul><ul><li>Carbon dioxide – moves from the body tissue into the blood, then from the blood into the lungs. </li></ul><ul><li>After eating – digested food molecules move from the small intestine into the blood. They then leave the blood and go into body tissue </li></ul>
  7. 9. 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 <ul><li>Good examples in the Human Body are:- </li></ul><ul><ul><li>Alveoli </li></ul></ul><ul><ul><li>Villi </li></ul></ul><ul><ul><li>Placenta </li></ul></ul><ul><ul><li>Neurones </li></ul></ul>
  8. 10. 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
  9. 11. Changing the rate of diffusion <ul><li>It can be increased by: </li></ul><ul><li>Increasing the surface area </li></ul><ul><li>Decreasing the diffusion distance </li></ul><ul><li>A greater concentration difference </li></ul>
  10. 13. Surfaces adapted for diffusion Villi <ul><li>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. </li></ul><ul><li>Villus – produce a large surface area, villi wall have folds (microvilli). Surface area of small intestine is approx 9 m 2 . </li></ul><ul><li>One cell thick, food does not have to far to diffuse into the blood </li></ul><ul><li>Good blood supply – means digested food is quickly taken away from villus so more can diffuse across to replace it </li></ul><ul><li>Membrane of villi is permeable, this means food molecules can pass through the membrane </li></ul>
  11. 14. Alveoli – in the lungs <ul><li>Breathing makes sure there is always a high concentration of oxygen in the alveoli. </li></ul><ul><li>Good blood supply makes sure as oxygen diffuses into the blood it is replaced with blood containing very little oxygen. </li></ul><ul><li>Alveolus is only one cell thick so the gases do not have far to travel </li></ul><ul><li>Large numbers of alveoli – this helps to increase the surface area, so more molecules can move across at any time. </li></ul><ul><li>Alveoli membrane is permeable to gases and is also moist; this helps to speed up diffusion. </li></ul>
  12. 15. Other substances adapted for diffusion <ul><li>Placenta </li></ul><ul><li>To move substances across the placenta as quickly as possible. To speed up movement, the placenta has: </li></ul><ul><li>A very large surface area </li></ul><ul><li>A very thin wall so substances only have a short distance to diffuse </li></ul><ul><li>The leaf </li></ul><ul><li>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. </li></ul><ul><li>Synapses </li></ul><ul><li>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. </li></ul>
  13. 16. The Alveoli in the Lungs Provide a Massive Surface Area for Exchange of Oxygen & Carbon Dioxide Alveoli

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