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Flashcards · Biology · Exchange Surfaces and Gas Exchange

Factors Affecting the Rate of Diffusion and Fick's Law

20 cards

  1. Name three factors that affect the rate of diffusion.

    The surface area, the concentration gradient and the diffusion distance (thickness).

  2. What happens to the rate of diffusion if the surface area is bigger?

    It increases, because more particles can cross at once.

  3. What happens to the rate of diffusion if the concentration difference is bigger?

    It increases, because the net movement is greater.

  4. What happens to the rate of diffusion if the membrane is thicker?

    It decreases, because the particles have further to go.

  5. What is Fick's law in words?

    The rate of diffusion is proportional to the surface area times the concentration difference, divided by the thickness of the membrane.

  6. What does the symbol \(\propto\) mean?

    Is proportional to.

  7. If the surface area doubles, what happens to the rate?

    It doubles.

  8. If the thickness doubles, what happens to the rate?

    It halves.

  9. If the concentration difference triples, what happens to the rate?

    It triples.

  10. What shape is the graph of rate against concentration difference?

    A straight line through the origin.

  11. What shape is the graph of rate against thickness?

    A curve that falls steeply and then levels off.

  12. What are arbitrary units?

    Units used for comparing values, such as the answer to a Fick's law calculation.

  13. Calculate the relative rate for area 8, difference 15 and thickness 4.

    \(8 \times 15 \div 4 = 30\) arbitrary units.

  14. Why does a thin barrier suit an exchange surface?

    The diffusion distance is short, so the rate is high.

  15. How do blood and breathing keep the gradient steep in the lungs?

    The blood carries oxygen away and breathing brings in fresh air.

  16. How are villi adapted for absorbing food?

    A large surface area, a wall one cell thick and a rich blood supply.

  17. Why does temperature affect diffusion?

    Particles have more energy at a higher temperature, so they move and diffuse faster.

  18. What is the common mistake with Fick's law?

    Multiplying by the thickness instead of dividing by it.

  19. Three pairs of boxes showing particles diffusing through a window in a divider, with no labels. Describe what each pair of boxes shows about the rate of diffusion. The same three pairs of boxes with headings and captions saying slower and faster.

    Left: a larger area makes diffusion faster. Middle: a bigger concentration difference makes diffusion faster. Right: a thinner membrane makes diffusion faster.

  20. Two graphs of the rate of diffusion, one a straight line and one a falling curve. Describe the relationship shown by each graph.

    Rate of diffusion is directly proportional to the concentration difference: a straight line through the origin. Rate of diffusion is inversely proportional to thickness: doubling the thickness halves the rate.