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Flashcards · Biology · Plant Structures and Transport

Measuring Transpiration

17 cards

  1. What does a potometer measure?

    The rate of water uptake by a shoot, which estimates transpiration.

  2. Why is the shoot cut under water?

    To stop air getting into the xylem and blocking it.

  3. What does the air bubble show?

    How much water the shoot has taken up.

  4. How do you work out the rate of uptake?

    Distance moved by the bubble ÷ time.

  5. What is the independent variable if you move a lamp?

    The distance of the lamp (the light intensity).

  6. What is the dependent variable in a potometer experiment?

    The distance the bubble moves in a set time.

  7. Name two control variables.

    Any two of the same shoot, same time, same temperature, same light or wind.

  8. Why repeat the experiment?

    To check the results are reliable and to calculate a mean.

  9. How can you increase the humidity around the shoot?

    Cover it with a clear plastic bag.

  10. Why is water uptake only an estimate of transpiration?

    Some of the water is used in photosynthesis and growth.

  11. How do you find the volume of water taken up?

    π r² × the distance the bubble moves.

  12. How do you make an impression of the stomata?

    Paint clear nail varnish on the leaf, then peel it off with sticky tape.

  13. How do you calculate the stomatal density?

    The number of stomata ÷ the area of the field of view.

  14. Why must the joints of the potometer be airtight?

    So that no air enters, which would move the bubble.

  15. What would a fan do to the rate?

    Increase it, by removing water vapour from around the leaf.

  16. A potometer with a pointer marked X to the air bubble. Name the part marked X and say what it shows.

    The air bubble. It moves along the capillary tube as the shoot takes up water, so its distance shows the water taken up.

  17. A potometer with no labels. Label the parts of the potometer. The same potometer with every part labelled.

    Leafy shoot, cut stem, airtight seal, air bubble, capillary tube, ruler and water reservoir.