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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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Homeostasis

  • In order to function properly and efficiently, organisms have different control systems that ensure their internal conditions are kept relatively constant

    • The process of maintaining constant internal body conditions is known as homeostasis

  • Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function

  • Examples of physiological factors that are controlled by homeostasis in mammals include:

    • Core body temperature

    • Metabolic waste (e.g. carbon dioxide and urea)

    • Blood pH

    • Concentration of glucose in the blood

    • Water potential of the blood

    • Concentration of the respiratory gases (carbon dioxide and oxygen) in the blood

Examiner Tips and Tricks

Learn the following definition for homeostasis: Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.

Principles of homeostasis

  • The majority of homeostatic control mechanisms in organisms use negative feedback to maintain homeostatic balance

    • This means keeping certain physiological factors, such as blood glucose concentration, within certain limits

  • Negative feedback control loops involve:

    • A receptor (or sensor)—to detect a stimulus that is involved with a condition or physiological factor

    • A coordination system (nervous system and endocrine system)—to transfer information between different parts of the body

    • An effector (muscles and glands)—to carry out a response

  • Outcome of a negative feedback loop:

    • The factor / stimulus is continuously monitored

    • If there is an increase in the factor, the body responds to make the factor decrease

    • If there is a decrease in the factor, the body responds to make the factor increase

Flowchart illustrating a negative feedback loop with internal and external stimuli. It involves receptors, central control, and effectors to maintain stability.
A flow diagram of a negative feedback control loop

  • Homeostasis in mammals relies on two different coordination systems to transfer information between different parts of the body:

    • Nervous system—information is transmitted as electrical impulses that travel along neurones

    • Endocrine system—information is transmitted as chemical messengers called hormones that travel in the blood

Examiner Tips and Tricks

Although the nervous and endocrine systems are both important in homeostasis and the regulation of certain physiological factors, there are some fundamental differences between them.

Information is transmitted through these two systems in different ways (electrical impulses vs. hormones).

Also, the nervous system is usually required for fast, but short-lived responses, whereas the endocrine system is usually involved in slower, but longer-lasting responses (although this is not always the case and some hormones can act very quickly)!