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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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Anaerobic adaptations of rice

  • Flooding is a major problem when growing crops

  • As the water rises and covers the different parts of a plant it can create problems:

    • Plant roots don’t get the oxygen they need for aerobic respiration

    • Plant leaves don’t get the carbon dioxide they need for photosynthesis

  • These gases are less readily available in water as they diffuse more slowly in liquid compared to air

  • Rice plants possess several adaptations that enable them to survive and grow in waterlogged conditions

Person in traditional straw hat planting rice seedlings in a flooded paddy field under bright sunlight, with green shoots visible.
Rice being planted in a waterlogged paddy field in Laos (Basile Morin, CC BY-SA 4.0, via Wikimedia Commons)

Adaptations for aerobic respiration

  • Some types of rice show an increased rate of upward growth away from the waterline

    • The leaves always remain above water so there is access to oxygen and carbon dioxide through the stomata

  • Rice plants possess aerenchyma tissue in the stems and roots

    • This specialised plant tissue contains useful air spaces that allow gases that enter the stomata to diffuse to other parts of the plant that are above and under the water

    • Oxygen and carbon dioxide can therefore be held in this tissue even when underwater and can be transferred from parts of the plant that have access to air

Adaptations for anaerobic respiration

  • When there isn’t enough energy being supplied to the cells by aerobic respiration, plants resort to anaerobic respiration as a source of ATP

  • Plants use ethanol fermentation during anaerobic respiration

    • Toxic ethanol is produced which can build up in the plant tissue causing damage

  • Rice plants can tolerate higher levels of toxic ethanol compared to other plants

  • They also produce more ethanol dehydrogenase

    • This is the enzyme that breaks down ethanol

  • The resilience that rice plants have towards ethanol allows them to carry out anaerobic respiration for longer so enough ATP is produced for the plant to survive and actively grow

Cross-section diagram of plant tissue, labelled with vascular tissues, air space, aerenchyma, and cells of the cortex, showing structural details.
Aerenchyma tissue in rice plants

Examiner Tips and Tricks

You might be wondering why farmers would grow rice in paddies (intentionally flooded fields). Growing rice in these conditions actually increases the yield. The plants or weeds that would usually be competitors for nutrients and light are unable to survive in these conditions and so the rice has more resources for its growth. Farmers are effectively removing selection pressures from the growing areas by flooding them.