The rate of transpiration of a leafy shoot can be measured with

Analyze the question: The question asks which instrument measures the rate of transpiration (water loss) in a leafy shoot.

Explain the concept: Transpiration is the loss of water vapour from plants, mainly through the stomata of leaves. Because a shoot takes up water to replace what it loses, the rate of water uptake is used to estimate the rate of transpiration. The instrument designed for this is the potometer.

How a potometer works:

1. A leafy shoot is cut under water, so no air bubble enters the xylem.
2. The shoot is fitted into the potometer, which is filled with water and has a thin capillary tube attached.
3. An air bubble is introduced into the capillary tube.
4. As the shoot transpires, it pulls water in, and the air bubble moves along the scale.
5. The distance the bubble travels in a given time shows the rate of water uptake, which approximates the rate of transpiration.

Checking each option:

• A. Anemometer: measures wind speed.
• B. Barometer: measures atmospheric pressure.
• C. Photometer: measures light intensity. It is not used for transpiration.
• D. Potometer: measures water uptake and so the rate of transpiration. ✔
• E. Thermometer: measures temperature.

Answer: D. Potometer

Exam tip: "Poto" sounds like "potable" (water), so a potometer goes with water uptake. Also remember that a potometer measures water uptake, which is only an approximation of transpiration, because not all the water absorbed is lost. Some is used in photosynthesis.