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  1. 1-biological-molecules

    1-1-biological-molecules-carbohydrates
    11 主题
  2. 1-2-biological-molecules-lipids
    3 主题
  3. 1-3-biological-molecules-proteins
    5 主题
  4. 1-4-proteins-enzymes
    12 主题
  5. 1-5-nucleic-acids-structure-and-dna-replication
    8 主题
  6. 1-6-atp-water-and-inorganic-ions
    4 主题
  7. 2-cell-structure
    2-1-cell-structure
    7 主题
  8. 2-2-the-microscope-in-cell-studies
    4 主题
  9. 2-3-cell-division-in-eukaryotic-and-prokaryotic-cells
    8 主题
  10. 2-4-cell-membranes-and-transport
    7 主题
  11. 2-5-cell-recognition-and-the-immune-system
    7 主题
  12. 2-6-vaccines-disease-and-monoclonal-antibodies
    6 主题
  13. 3-exchange-and-transport
    3-1-adaptations-for-gas-exchange
    6 主题
  14. 3-2-human-gas-exchange
    10 主题
  15. 3-3-digestion-and-absorption
    5 主题
  16. 3-4-mass-transport-in-animals
    6 主题
  17. 3-5-the-circulatory-system-in-animals
    8 主题
  18. 3-6-mass-transport-in-plants
    6 主题
  19. 4-genetics-variation-and-interdependence
    4-1-dna-genes-and-chromosomes
    7 主题
  20. 4-2-dna-and-protein-synthesis
    6 主题
  21. 4-3-genetic-diversity-mutations-and-meiosis
    7 主题
  22. 4-4-genetic-diversity-and-adaptation
    6 主题
  23. 4-5-species-and-taxonomy
    4 主题
  24. 4-6-biodiversity
    9 主题
  25. 5-energy-transfers-in-and-between-organisms-a-level-only
    5-1-photosynthesis-a-level-only
    5 主题
  26. 5-2-respiration-a-level-only
    7 主题
  27. 5-3-energy-and-ecosystems-a-level-only
    9 主题
  28. 5-4-nutrient-cycles-a-level-only
    4 主题
  29. 6-organisms-respond-to-changes-in-their-environments-a-level-only
    6-1-response-to-stimuli-a-level-only
    12 主题
  30. 6-2-nervous-coordination-a-level-only
    10 主题
  31. 6-3-skeletal-muscles-a-level-only
    6 主题
  32. 6-4-homeostasis-a-level-only
    11 主题
  33. 7-genetics-populations-evolution-and-ecosystems-a-level-only
    7-1-inheritance-a-level-only
    6 主题
  34. 7-2-populations-a-level-only
    3 主题
  35. 7-3-evolution-a-level-only
    5 主题
  36. 7-4-populations-in-ecosystems-a-level-only
    7 主题
  37. 8-the-control-of-gene-expression-a-level-only
    8-1-genetic-mutations-a-level-only
    2 主题
  38. 8-2-regulation-of-gene-expression-a-level-only
    11 主题
  39. 8-3-using-genome-projects-a-level-only
    4 主题
  40. 8-4-gene-technologies-a-level-only
    13 主题
  41. exam-guidance-and-skills
    essay-guidance
    3 主题
  1. Biology_A-level_Aqa
  2. 1-4-proteins-enzymes
  3. 1-4-6-using-a-tangent-to-find-initial-rate-of-reaction
课 4, 主题 6
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1-4-6-using-a-tangent-to-find-initial-rate-of-reaction

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Using a tangent to find the initial rate of reaction

  • For linear graphs (i.e. graphs with a straight line), the gradient is the same throughout

    • This makes it easy to calculate the rate of change (rate of change = change ÷ time)

  • The initial rate of reaction is the rate of reaction at the start of the line (i.e. where time = 0)

  • However, many enzyme rate experiments produce non-linear graphs (i.e. graphs with a curved line), meaning they have an ever-changing gradient

    • They are shaped this way because the reaction rate is changing over time

  • In these cases, a tangent can be used to find the reaction rate at any one point on the graph:

Worked Example

The graph below shows the results of an enzyme-catalysed reaction. Using this graph, calculate the initial rate of reaction.

Tangent initial reaction rate (1), downloadable AS & A Level Biology revision notes

Step 1: Estimate the extrapolated curve of the graph

Tangent initial reaction rate (2), downloadable AS & A Level Biology revision notes

Step 2: Find the tangent to the curve at 0 seconds (the start of the reaction)

Tangent initial reaction rate (3), downloadable AS & A Level Biology revision notes
Tangent initial reaction rate (4), downloadable AS & A Level Biology revision notes

The tangent drawn in the graph above shows that 72 cm3 of product was produced in the first  20 seconds.

Step 3: Calculate the gradient of the tangent (this will give you the initial rate of reaction):

Gradient = change in y-axis ÷ change in x-axis

Initial rate of reaction = 72 cm3 ÷ 20 s

Initial rate of reaction = 3.6 cm3 s-1

Examiner Tips and Tricks

When drawing a tangent, use a ruler and pencil to draw a perfectly straight line that just touches the curve at the chosen point. Make sure the curve remains visible (not hidden under the ruler).

To calculate the gradient, remember this handy phrase:
“Rise over run” – divide the vertical change by the horizontal change.