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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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Ultrastructure of striated muscle

  • Striated muscle makes up the muscles in the body that are attached to the skeleton

    • ‘Striated’ means it is striped/streaky in appearance

Histological slide of skeletal muscle tissue showing elongated muscle fibres in pink with multiple nuclei, and visible striations and connective tissue.
Skeletal striated muscle as seen under the microscope, after staining Image by Nephron, CC BY-SA 3.0, via Wikimedia Commons

  • Striated muscle is made up of muscle fibres

  • A muscle fibre is a highly specialised cell-like unit:

    • Each muscle fibre contains an organised arrangement of contractile proteins in the cytoplasm

    • Each muscle fibre is surrounded by a cell surface membrane

    • Each muscle fibre contains many nuclei—this is why muscle fibres are not usually referred to as cells

  • The different parts of a muscle fibre have different names from the equivalent parts of a normal cell:

    • Cell surface membrane = sarcolemma

    • Cytoplasm = sarcoplasm

  • The sarcoplasm contains mitochondria and myofibrils

    • The mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction

    • Myofibrils are bundles of actin and myosin filaments, which slide past each other during muscle contraction

Diagram of muscle structure showing muscle fibres, tendon attachment, nuclei, sarcolemma, T-tubule, mitochondrion, sarcoplasmic reticulum, and myofibrils.
The ultrastructure of striated muscle and of a section of muscle fibre

Myofibrils

  • Myofibrils are located in the sarcoplasm

  • Each myofibril is made up of two types of protein filament:

    • Thick filaments made of myosin

    • Thin filaments made of actin

  • These two types of filament are arranged in a particular order, creating different types of band and line

Part of myofibril

Description

H band

Only thick myosin filaments present

I band

Only thin actin filaments present

A band

Contains areas where only myosin filaments are present and areas where myosin and actin filaments overlap

M Line

Attachment for myosin filaments

Z line

Attachment for actin filaments

Sarcomere

The section of myofibril between two Z lines
Diagram of a sarcomere showing myofibril structure with thick myosin filaments and thin actin filaments, including Z line, M line, A band, I band, and H band.
The structure of a myofibril