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Biology_A-level_Cie

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  1. 1-1-the-microscope-in-cell-studies
    5 主题
  2. 1-2-cells-as-the-basic-units-of-living-organisms
    5 主题
  3. 2-1-testing-for-biological-molecules
    3 主题
  4. 2-2-carbohydrates-and-lipids
    8 主题
  5. 2-3-proteins
    6 主题
  6. 2-4-water
    2 主题
  7. 3-1-mode-of-action-of-enzymes
    5 主题
  8. 3-2-factors-that-affect-enzyme-action
    8 主题
  9. 4-1-fluid-mosaic-membranes
    4 主题
  10. 4-2-movement-into-and-out-of-cells
    12 主题
  11. 5-1-replication-and-division-of-nuclei-and-cells
    6 主题
  12. 5-2-chromosome-behaviour-in-mitosis
    2 主题
  13. 6-1-structure-of-nucleic-acids-and-replication-of-dna
    4 主题
  14. 6-2-protein-synthesis
    5 主题
  15. 7-1-structure-of-transport-tissues
    4 主题
  16. 7-2-transport-mechanisms
    7 主题
  17. 8-1-the-circulatory-system
    7 主题
  18. 8-2-transport-of-oxygen-and-carbon-dioxide
    5 主题
  19. 8-3-the-heart
    4 主题
  20. 9-1-the-gas-exchange-system
    6 主题
  21. 10-1-infectious-diseases
    3 主题
  22. 10-2-antibiotics
    3 主题
  23. 11-1-the-immune-system
    4 主题
  24. 11-2-antibodies-and-vaccination
    6 主题
  25. 12-1-energy
    5 主题
  26. 12-2-respiration
    11 主题
  27. 13-1-photosynthesis-as-an-energy-transfer-process
    8 主题
  28. 13-2-investigation-of-limiting-factors
    2 主题
  29. 14-1-homeostasis-in-mammals
    8 主题
  30. 14-2-homeostasis-in-plants
    3 主题
  31. 15-1-control-and-coordination-in-mammals
    12 主题
  32. 15-2-control-and-coordination-in-plants
    3 主题
  33. 16-1-passage-of-information-from-parents-to-offspring
    5 主题
  34. 16-2-the-roles-of-genes-in-determining-the-phenotype
    7 主题
  35. 16-3-gene-control
    3 主题
  36. 17-1-variation
    4 主题
  37. 17-2-natural-and-artificial-selection
    7 主题
  38. 17-3-evolution
    2 主题
  39. 18-1-classification
    5 主题
  40. 18-2-biodiversity
    7 主题
  41. 18-3-conservation
    6 主题
  42. 19-1-principles-of-genetic-technology
    11 主题
  43. 19-2-genetic-technology-applied-to-medicine
    4 主题
  44. 19-3-genetically-modified-organisms-in-agriculture
    2 主题
  45. 1-1-the-microscope-in-cell-studies
  46. 1-2-cells-as-the-basic-units-of-living-organisms
  47. 2-1-testing-for-biological-molecules
  48. 2-2-carbohydrates-and-lipids
  49. 2-3-proteins
  50. 2-4-water
  51. 3-1-mode-of-action-of-enzymes
  52. 3-2-factors-that-affect-enzyme-action
  53. 4-1-fluid-mosaic-membranes
  54. 4-2-movement-into-and-out-of-cells
  55. 5-1-replication-and-division-of-nuclei-and-cells
  56. 5-2-chromosome-behaviour-in-mitosis
  57. 6-1-structure-of-nucleic-acids-and-replication-of-dna
  58. 6-2-protein-synthesis
  59. 7-1-structure-of-transport-tissues
  60. 7-2-transport-mechanisms
  61. 8-1-the-circulatory-system
  62. 8-2-transport-of-oxygen-and-carbon-dioxide
  63. 8-3-the-heart
  64. 9-1-the-gas-exchange-system
  65. 10-1-infectious-diseases
  66. 10-2-antibiotics
  67. 11-1-the-immune-system
  68. 11-2-antibodies-and-vaccination
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Resolution & magnification

Magnification

  • Magnification is the number of times that a real-life specimen has been enlarged to give a larger view/image

    • E.g. a magnification of x100 means that a specimen has been enlarged 100 times to give the image shown

  • A light microscope has two types of lens which allow it to achieve different levels of magnification:

    • An eyepiece lens, which often has a magnification of x10

    • A series of objective lenses, each with a different magnification, e.g. x4, x10, x40 and x100

  • To calculate the total magnification of a specimen being viewed, the magnification of the eyepiece lens and the objective lens are multiplied together:

Total magnification = eyepiece lens magnification x objective lens magnification

Resolution

  • The resolution of a microscope is its ability to distinguish two separate points on an image as separate objects; this determines the ability of a microscope to show detail

    • If resolution is too low then two separate objects will be observed as one point, and an image will appear blurry, or an object will not be visible at all

    • The resolution of a microscope limits the magnification that it can usefully achieve; there is no point in increasing the magnification to a higher level if the resolution is poor

  • The resolution of a light microscope is limited by the wavelength of light

    • Visible light falls within a set range of light wavelengths; 400-700 nm

    • The resolution of a light microscope cannot be smaller than half the wavelength of visible light

      • The shortest wavelength of visible light is 400 nm, so the maximum resolution of a light microscope is 200 nm

    • E.g. the structure of a phospholipid bilayer cannot be observed under a light microscope due to low resolution:

      • The width of the phospholipid bilayer is about 10 nm

      • The maximum resolution of a light microscope is 200 nm, so any points that are separated by a distance of less than 200 nm, such as the 10 nm phospholipid bilayer, cannot be resolved by a light microscope and therefore will not be distinguishable as separate objects

  • Electron microscopes have a much higher resolution, and therefore magnification, than light microscopes as electrons have a much smaller wavelength than visible light

    • Electron microscopes can achieve a resolution of 0.5 nm

Diagram comparing light and electron microscopes; includes details on wavelengths and sizes, such as ribosomes and mitochondria, with annotations.
The resolving power of electron microscopes is much greater than that of light microscopes due to the smaller wavelength of electrons in comparison to visible light

Examiner Tips and Tricks

Don’t assume that increasing magnification will let you see more detail — it won’t if the resolution is too low.

Remember: magnification makes things bigger, resolution makes things clearer.