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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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Closed double circulatory system

The need for a circulatory system

  • The cells of all living organisms need a constant supply of reactants for metabolism, e.g. oxygen and glucose

  • Single celled organisms can gain oxygen and glucose directly from their surroundings

    • The molecules can diffuse to all parts of the cell quickly due to short diffusion distances

  • Larger organisms, however, are made up of many layers of cells

    • This means that the time taken for substances such as glucose and oxygen to diffuse to every cell in the body would be far too long

      • The diffusion distances involved are too great

  • To solve this problem their exchange surfaces are connected to a mass transport system, for example

    • The digestive system is connected to the circulatory system

    • The lungs are connected to the circulatory system

  • Mass transport is the bulk movement of gases or liquids in one direction, usually via a system of vessels and tubes

  • The circulatory system in mammals is a well-studied example of a mass transport system

    • The one-way flow of blood within the blood vessels carries essential nutrients and gases to all the cells of the body

Open and closed systems

  • Circulatory systems are either described as being open or closed

  • In a closed circulatory system, blood is pumped around the body and is always contained within a network of blood vessels

    • All vertebrates and many invertebrates have closed circulatory systems

  • In an open circulatory system, blood is not contained within blood vessels but is pumped directly into body cavities

    • Organisms such as arthropods and molluscs have open circulatory systems

  • Humans have a closed double circulatory system:

    • In one complete circuit of the body blood passes through the heart (the pump) twice

  • The right side of the heart pumps deoxygenated blood to the lungs for gas exchange

    • This is the pulmonary circulatory system

  • Blood then returns to the left side of the heart, so that oxygenated blood can be pumped efficiently (at high pressure) around the body

    • This is the systemic circulatory system

Diagram of blood circulation showing oxygenated and deoxygenated flow between the lungs, heart, and body tissues, with labelled components.
The double circulatory system in mammals showing pulmonary and systemic circulation

Structure

Function

Heart

A hollow, muscular organ located in the chest cavity which pumps blood. Cardiac muscle tissue is specialised for repeated involuntary contraction without rest.

Arteries

Blood vessels which carry blood away from the heart. The walls of the arteries contain lots of muscle and elastic tissue and a narrow lumen, to maintain high blood pressure.

Arterioles

Small arteries which branch from larger arteries and connect to capillaries.

Capillaries

Tiny blood vessels which connect arterioles and venules. Their size means they pass directly past cells and tissues and perform gas exchange and exchange of substances such as glucose.

Venules

Small veins which join capillaries to larger veins.

Veins

Blood vessels which carry blood back towards the heart. The walls of veins are thin in comparison to arteries, having less muscle and elastic tissue but a wider lumen. Valves help maintain blood flow back towards the heart.

Examiner Tips and Tricks

Make sure you study any circulatory diagrams in the exam carefully to distinguish between single and double circulatory systems.