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Flashcards · Biology · Transport in Cells

Surface Area to Volume Ratio and Exchange Surfaces

23 cards

  1. What is surface area to volume ratio?

    The surface area of an object divided by its volume.

  2. What happens to the ratio as an object gets bigger?

    It gets smaller.

  3. What is the surface area of a cube with 2 cm sides?

    24 cm², because \(6 \times 2 \times 2\).

  4. What is the volume of a cube with 3 cm sides?

    27 cm³, because \(3 \times 3 \times 3\).

  5. What is the surface area to volume ratio of a 3 cm cube?

    2 : 1, from 54 ÷ 27.

  6. Why can a single-celled organism exchange materials by diffusion across its surface?

    It has a large surface area to volume ratio, so substances reach the whole cell fast enough.

  7. Why can't a large organism rely on diffusion across its outer surface?

    Its surface area to volume ratio is small, so substances would take too long to reach the cells in the middle.

  8. What two things do large organisms have to solve this problem?

    Exchange surfaces and a transport system.

  9. Name the four features of an effective exchange surface.

    A large surface area, a thin membrane, an efficient blood supply (animals) and ventilation (animals, for gas exchange).

  10. Why does a thin membrane help?

    It gives a short diffusion path.

  11. Why does a good blood supply help?

    It carries substances away, keeping the concentration gradient steep.

  12. Why does ventilation help?

    It keeps the concentration of the gas high on the outside, keeping the gradient steep.

  13. What are villi?

    Finger-like folds in the lining of the small intestine that give a large surface area.

  14. What are alveoli?

    The tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged.

  15. How are the lungs ventilated?

    By breathing.

  16. How are the gills of a fish ventilated?

    Water flows over them all the time.

  17. How are root hair cells adapted?

    They have a long thin extension, which gives a large surface area.

  18. How are leaves adapted for gas exchange?

    They are flat and thin, with air spaces inside and stomata in the surface.

  19. What are stomata?

    Tiny pores in the leaf surface that let carbon dioxide in and oxygen out.

  20. Which exchange surfaces are not supplied with blood?

    Those of plants: the roots and the leaves.

  21. Three cubes of side 1, 2 and 3 cm with nothing else written on the page. Work out the surface area to volume ratio of each cube. Three cubes with their surface areas, volumes and ratios of 6 to 1, 3 to 1 and 2 to 1.

    1 cm: 6 cm² ÷ 1 cm³ = 6 : 1. 2 cm: 24 ÷ 8 = 3 : 1. 3 cm: 54 ÷ 27 = 2 : 1. The bigger the cube, the smaller the ratio.

  22. Five numbered pictures of exchange surfaces with no captions. Describe how each of these exchange surfaces is adapted. The five exchange surfaces described, with the features they share.

  23. A single cell beside a large block of cells with a question mark at its centre. Why do the middle cells of a large organism need an exchange surface and a transport system?

    Its surface area to volume ratio is small, so diffusion from the outside would be too slow to reach them. Exchange surfaces and a transport system get substances to every cell.