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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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Test strips & biosensors

Measuring urine glucose concentration

  • People with diabetes cannot control their blood glucose concentration so that it remains within normal, safe limits

  • The presence of glucose in urine is an indicator that a person may have diabetes

    • If blood glucose concentration increases above a value known as the renal threshold, not all of the glucose from the filtrate in the proximal convoluted tubule is reabsorbed and some will be left in the urine

  • Test strips can be used to test urine for the presence and concentration of glucose

  • Two enzymes are immobilised on a small pad at one end of the test strip:

    • glucose oxidase

    • peroxidase

  • The pad is immersed in the urine sample for a short time

  • If glucose is present:

    • Glucose oxidase catalyses a reaction in which glucose is oxidised to form gluconic acid and hydrogen peroxide

    • Peroxidase then catalyses a reaction between the hydrogen peroxide and a colourless chemical in the pad to form a brown compound and water

  • The colour of the pad is compared to a colour chart

    • Different colours represent different concentrations of glucose (the higher the concentration of glucose present, the darker the colour)

  • Urine tests only show whether or not the blood glucose concentration was above the renal threshold whilst urine was collecting in the bladder

    • They do not indicate the current blood glucose concentration

Flowchart showing glucose reactions in urine. Includes enzymes glucose oxidase and peroxidase, colour change on test strip indicating glucose levels.
Top: the chemical reactions catalysed by the immobilised glucose oxidase and peroxidase enzymes on the end-pad of a urine test strip. Bottom: an example of the colour chart used to interpret the colour of the end-pad of a urine test strip.

Measuring blood glucose concentration

  • A biosensor can be used by people with diabetes to show their current blood glucose concentration

  • Similar to the test strips, a biosensor uses glucose oxidase (but no peroxidase) immobilised on a recognition layer

  • Covering the recognition layer is a partially permeable membrane that only allows small molecules from the blood to reach the immobilised enzymes

  • When a small sample of blood is tested, glucose oxidase catalyses a reaction in which any glucose in the blood sample is oxidised to form gluconic acid and hydrogen peroxide

  • The hydrogen peroxide produced is oxidised at an electrode that detects electron transfers

  • The electron flow is proportional to the glucose concentration of the blood sample

  • The biosensor amplifies the current, which is then read by a processor to produce a digital reading for blood glucose concentration

  • This process is complete within a matter of seconds

Diagram showing a biosensor detecting blood glucose levels. Glucose oxidase reacts with glucose, producing hydrogen peroxide, read on a digital display.
The parts of a glucose biosensor

Examiner Tips and Tricks

The urine test strip will only produce a positive result for glucose. Other sugars such as fructose, sucrose and lactose will give a negative result. This is due to the specificity of the glucose oxidase enzyme.