Biology HL IA - Transpiration lab report

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Biology HL

Candidate name: Ieva Drūlytė

Date: ___________________

Investigation into the transpiration rate of maple dependency on the area of leaves



Transpiration is the evaporation of water particles from plant surfaces, especially from the surface openings, or stomata, on leaves.  Stomatal transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the surfaces of the epidermal cells of the leaves. The amount of water given off depends somewhat upon how much water the roots of the plant have absorbed.  It also depends upon such environmental conditions as sunlight, humidity, winds and temperature.  A plant should not be transplanted in full sunshine because it may lose too much water and wilt before the damaged roots can supply enough water. Transpiration occurs as the sun warms the water inside the blade.  The warming changes much of the water into water vapor.  This gas can then escape through the stomata.  Transpiration helps cool the inside of the leaf because the escaping vapor has absorbed heat.


Aim: to investigate the effect of altering the leaves area on the rate of transpiration of Acer (Maple).

Hypothesis: with decreasing area of leaves provided, the rate of transpiration would also decrease as transpiration occurs through stomata which are located commonly on the lower epidermis of leaves.

Variables: the rate of transpiration (the amount of H2O taken, mm) (dependent variable) will be altered by reducing the area of leaves (cm2) (independent variable).

Table 1 Controlled variables.

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  1. Maple branch
  2. 1 mL pipette; 0.01 divisions (±0.005)
  3. Test tube
  4. Glass tube
  5. Rubber bung with hole
  6. Stand with clamps and bosses
  7. Razor blade
  8. Stop-watch
  9. Water
  10. Plasticine


First, maple tree branch of the appropriate size to fit photometer was collected. It had to be cut under the water to prevent oxygen getting into the xylem. Then, the photometer was constructed from the test tube, plastic tube, and measuring pipette and filled up with water so that any air bubbles were removed from the tubing. After that, the end of the branch of maple tree ...

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