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Biology AS CIE

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  1. 1-cell-structure
    10 主题
  2. 2-biological-molecules
    19 主题
  3. 3-enzymes
    13 主题
  4. 4-cell-membranes-and-transport
    16 主题
  5. 5-the-mitotic-cell-cycle
    8 主题
  6. 6-nucleic-acids-and-protein-synthesis
    9 主题
  7. 7-transport-in-plants
    11 主题
  8. 8-transport-in-mammals
    16 主题
  9. 9-gas-exchange
    6 主题
  10. 10-infectious-diseases
    6 主题
  11. 11-immunity
    10 主题
课 4, 主题 5
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4-2-movement-into-and-out-of-cells AS investigating-surface-area

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Exam code:9700

Investigating SA with agar

  • The effect of changing surface area to volume ratio on diffusion can be investigated by timing the diffusion of ions through cubes of agar of different sizes

Method

  • Coloured agar is made up and cut into cubes of the required dimensions (eg. 0.5 cm × 0.5 cm × 0.5 cm, 1 cm × 1 cm × 1 cm and 2 cm × 2 cm × 2 cm)

  • The surface area, volume and surface area to volume ratio of these cubes is calculated and recorded

  • The cubes are then placed into boiling tubes containing a diffusion solution (such as dilute hydrochloric acid)

    • The same volume of dilute hydrochloric acid should be measured carefully into each boiling tube

    • The acid should have higher concentration than the sodium hydroxide so that its diffusion can be monitored by a change in colour of the indicator in the agar blocks

  • Measurements can be taken of either:

    • The time taken for the acid to completely change the colour of the indicator in the agar blocks

    • The distance travelled into the block by the acid (shown by the change in colour of the indicator) in a given time (e.g., 5 minutes)

Diagram showing steps for a diffusion experiment with agar cubes, detailing cutting, calculating surface area, immersing in acid, and timing colour change.
The steps used to investigate the effect of changing the surface area to volume ratio on diffusion

Analysis

  • If the time taken for the acid to completely change the colour of the indicator in the agar blocks is recorded, these times can be converted to rates

  • A graph could be plotted showing how the rate of diffusion (rate of colour change) changes with the surface area : volume ratio of the agar cubes

Table of diffusion rates in agar cubes with a graph plotting rate versus surface area to volume ratio, accompanied by a conclusion about the relationship.
To analyse the results of the investigation, calculate the rates of diffusion before plotting a graph for rate of diffusion against surface area : volume ratio

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