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  1. 1-biological-molecules

    1-1-biological-molecules-carbohydrates
    11 主题
  2. 1-2-biological-molecules-lipids
    3 主题
  3. 1-3-biological-molecules-proteins
    5 主题
  4. 1-4-proteins-enzymes
    12 主题
  5. 1-5-nucleic-acids-structure-and-dna-replication
    8 主题
  6. 1-6-atp-water-and-inorganic-ions
    4 主题
  7. 2-cell-structure
    2-1-cell-structure
    7 主题
  8. 2-2-the-microscope-in-cell-studies
    4 主题
  9. 2-3-cell-division-in-eukaryotic-and-prokaryotic-cells
    8 主题
  10. 2-4-cell-membranes-and-transport
    7 主题
  11. 2-5-cell-recognition-and-the-immune-system
    7 主题
  12. 2-6-vaccines-disease-and-monoclonal-antibodies
    6 主题
  13. 3-exchange-and-transport
    3-1-adaptations-for-gas-exchange
    6 主题
  14. 3-2-human-gas-exchange
    10 主题
  15. 3-3-digestion-and-absorption
    5 主题
  16. 3-4-mass-transport-in-animals
    6 主题
  17. 3-5-the-circulatory-system-in-animals
    8 主题
  18. 3-6-mass-transport-in-plants
    6 主题
  19. 4-genetics-variation-and-interdependence
    4-1-dna-genes-and-chromosomes
    7 主题
  20. 4-2-dna-and-protein-synthesis
    6 主题
  21. 4-3-genetic-diversity-mutations-and-meiosis
    7 主题
  22. 4-4-genetic-diversity-and-adaptation
    6 主题
  23. 4-5-species-and-taxonomy
    4 主题
  24. 4-6-biodiversity
    9 主题
  25. 5-energy-transfers-in-and-between-organisms-a-level-only
    5-1-photosynthesis-a-level-only
    5 主题
  26. 5-2-respiration-a-level-only
    7 主题
  27. 5-3-energy-and-ecosystems-a-level-only
    9 主题
  28. 5-4-nutrient-cycles-a-level-only
    4 主题
  29. 6-organisms-respond-to-changes-in-their-environments-a-level-only
    6-1-response-to-stimuli-a-level-only
    12 主题
  30. 6-2-nervous-coordination-a-level-only
    10 主题
  31. 6-3-skeletal-muscles-a-level-only
    6 主题
  32. 6-4-homeostasis-a-level-only
    11 主题
  33. 7-genetics-populations-evolution-and-ecosystems-a-level-only
    7-1-inheritance-a-level-only
    6 主题
  34. 7-2-populations-a-level-only
    3 主题
  35. 7-3-evolution-a-level-only
    5 主题
  36. 7-4-populations-in-ecosystems-a-level-only
    7 主题
  37. 8-the-control-of-gene-expression-a-level-only
    8-1-genetic-mutations-a-level-only
    2 主题
  38. 8-2-regulation-of-gene-expression-a-level-only
    11 主题
  39. 8-3-using-genome-projects-a-level-only
    4 主题
  40. 8-4-gene-technologies-a-level-only
    13 主题
  41. exam-guidance-and-skills
    essay-guidance
    3 主题
  1. Biology_A-level_Aqa
  2. 3-2-human-gas-exchange
  3. 3-2-3-microscopy-and-gas-exchange-surfaces
课 14, 主题 3
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3-2-3-microscopy-and-gas-exchange-surfaces

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Examining gas exchange surfaces

  • School students may use pre-prepared microscope slides to view gas exchange tissue under an optical microscope

Mammalian gas exchange tissue

  • Thin sections of mammalian lung tissue may display the following features:

    • alveoli that differ in size and shape

    • alveolar walls that are:

      • one cell thick

      • made up of flattened cells

    • nuclei that are shown as dark dots

    • blood vessels in between the alveoli

Histological slide showing lung tissue with labelled blood vessel and alveolus, highlighted in pink and purple hues; scale bar indicates 100 micrometres.
Mammalian lung specimens may show alveoli, alveolar walls and blood vessels

Fish gas exchange tissue

  • Thin sections of fish gill tissue may display the following features:

    • the gill arch which provides a backbone for the gill filaments

    • many filaments arranged along the gill arch

    • lamellae visible at higher power

Microscopic view of a fish gill showing pink and purple filaments, lamellae, and gill arch, with each part labelled for educational purposes.
The gill arch, filaments and gill lamellae may be visible under an optical microscope

Insect gas exchange tissue

  • Electron microscopes can take clear images of insect gas exchange structures, e.g. the spiracles

Illustration shows a close-up of an insect spiracle, surrounded by textured exoskeleton. Label with an arrow points to the spiracle.
Scanning electron microscopes can generate 3D images of insect gas exchange features

Dicotyledonous leaves

  • A section of stained tissue from a dicotyledonous leaf can allow the following features to be viewed:

    • waxy cuticle

    • epidermal layers

    • palisade mesophyll layer

    • spongy mesophyll layer

    • stomata

    • guard cells

Cross-section of a leaf showing labelled layers: upper epidermis, waxy cuticle, palisade mesophyll, spongy mesophyll, lower epidermis, and guard cells.
Optical microscopes can be used to view the internal tissues within a dicotyledonous leaf

Examiner Tips and Tricks

Textbook diagrams and microscope specimens do not always look exactly the same, so be sure to get plenty of practice at identifying key features as viewed under a microscope, as well as learning them from the original diagrams.