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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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Investigating RQs

  • Respirometers are used to measure and investigate the rate of oxygen consumption during respiration in organisms

  • They can also be used to calculate respiratory quotients

  • The experiments usually involve organisms such as germinating seeds or invertebrates

Diagram showing respirometer with experimental and control tubes. Experimental tube has blowfly larvae; control tube has glass beads. Manometer measures pressure.
The typical set-up of a respirometer

The equation for calculating a change in gas volume

  • The volume of oxygen consumed (cm3 min-1) can be worked out using:

    • The diameter of the capillary tube r (cm)

    • And the distance moved by the manometer fluid h (cm) in a minute

  • Using the formula:

πr2h

Using a respirometer to determine the respiratory quotient

Method

  • Measure oxygen consumption: set up the respirometer and run the experiment with soda-lime present in both tubes. Use the manometer reading to calculate the change in gas volume within a given time, x cm3 min-1

    • Always read from the side of the U-tube manometer closest to the respiring organisms (the left side as depicted in this diagram)

  • Reset the apparatus: allow air to re-enter the tubes via the screw cap and reset the manometer fluid using the syringe

  • Run the experiment again: remove the soda-lime from both tubes and use the manometer reading to calculate the change in gas volume in a given time, y cm3 min-1

Calculations

  • x tells us the volume of oxygen consumed by respiration within a given time

  • y tells us the volume of oxygen consumed by respiration within a given time minus the volume of carbon dioxide produced within a given time

    • (x – y) is therefore the volume of CO2 given off by the organisms 

    • remembering to read the scale on the side of the U-tube manometer closest to the respiring organisms

  • The two measurements x and y can be used to calculate the RQ

Equation image showing RQ as CO2/O2. Below, RQ is shown as (x−y)/x.
RQ Equation for Respirometer experiment

Worked Example

Calculating RQ from a respirometer experiment

x = 2.9 cm3 min-1

y = 0.8 cm3 min-1

fraction numerator straight x minus straight y over denominator straight x end fraction equals RQ

fraction numerator 2.9 minus 0.8 over denominator 2.9 end fraction equals 0.724

When equal volumes of oxygen are consumed and carbon dioxide produced (as seen with glucose) the manometer fluid will not move and y will be 0, making the RQ=1.

Analysis

  • Respirometers can be used in experiments to investigate how different factors affect the RQ of organisms over time

    • e.g. temperature – using a series of water baths

  • When an RQ value changes it means the substrate being respired has changed

  • Some cells may also be using a mixture of substrates in respiration e.g. An RQ value of 0.85 suggests both carbohydrates and lipids are being used at the same time

    • This is because the RQ of glucose is 1 and the RQ of lipids is 0.7

  • Under normal cellular conditions, the order which substrates are used in respiration is: carbohydrates, lipids and proteins

  • The RQ can also give an indication of under or overfeeding:

    • An RQ value of more than 1 suggests excessive carbohydrate/calorie intake

    • An RQ value of less than 0.7 suggests underfeeding

Examiner Tips and Tricks

There are several ways you can manage variables and increase the reliability of results in respirometer experiments:

  • Use a controlled water bath to keep the temperature constant

  • Have a control tube with an equal volume of inert material to the volume of the organisms to compensate for changes in atmospheric pressure

  • Repeat the experiment multiple times and calculate a mean