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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
  1. Biology_A-level_Cie
  2. 12-1-energy
  3. respiratory-quotient-rq
课 25, 主题 4
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respiratory-quotient-rq

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Respiratory quotient (RQ)

  • The respiratory quotient (RQ) is: the ratio of carbon dioxide molecules produced to oxygen molecules taken in during respiration

 RQ equals CO subscript 2 over straight O subscript 2

Diagram of human head and respiratory system showing oxygen inhalation and carbon dioxide exhalation with formula for respiratory quotient (RQ).
The formula for the Respiratory Quotient

RQ values of different respiratory substrates

  • Carbohydrates, lipids and proteins have different typical RQ values

  • This is because the number of carbon-hydrogen bonds differs in each type of biological molecule

    • A higher number of carbon-hydrogen bonds means that more hydrogen atoms can be used to create a proton gradient

    • More hydrogens means that more ATP molecules can be produced by chemiosmosis

    • More oxygen is therefore required to break down the molecule (in the last step of oxidative phosphorylation to form water)

  • When glucose is respired aerobically, equal volumes of carbon dioxide are produced and oxygen taken in, meaning it has an RQ value of 1

Glucose RQ

Respiratory substrate

Typical RQ value

Carbohydrate

1.0

Protein

0.8 – 0.9

Lipid

0.7

Examiner Tips and Tricks

Some questions may ask you to suggest what substrate is being respired during an experiment based on the RQ value—so make yourself familiar with the values in the table.

Calculating RQs

  • The respiratory quotient is calculated from respiration equations

  • It involves comparing the ratios of carbon dioxide given out to oxygen taken in

  • The formula for this is:

RQ Maths Equation, downloadable AS & A Level Biology revision notes

Equation to calculate the RQ

  • If you know the molecular formula of the substrate being aerobically respired then you can create a balanced equation to calculate the RQ value

  • In a balanced equation the number before the chemical formula can be taken as the number of molecules/moles of that compound

    • This is because the same number of molecules of any gas take up the same volume e.g. 12 molecules of carbon dioxide take up the same volume as 12 molecules of oxygen

  • Glucose has a simple 1:1 ratio and RQ value of 1 but other substrates have more complex ratios leading to different RQ values

Worked Example

RQ for a lipid

Linoleic acid (a fatty acid found in nuts) has the molecular formula C18H32O2

Step 1: Create a respiration equation

C18H32O2 + O2 → CO2 + H2O

Step 2: Balance the equation

C × 18 C × 1

H × 32 H × 2

O × 4 O × 3

Step 3: Create the full equation

C18H32O2 + 25O2 → 18CO2 + 16H2O

Step 3: Use the RQ formula

CO subscript 2 over open parentheses straight O close parentheses subscript 2 equals RQ

<img alt=”18 over 25 equals 0.72″ data-mathml='<math style=”font-family:Arial” ><semantics><mrow><mfrac><mn>18</mn><mn>25</mn></mfrac>&lt