The instrument used to measure the rate of transpiration in plants is called a/an

Step 1: Analyze the question The question asks for the instrument that measures the rate of transpiration (water loss from plants through the stomata).

Step 2: Review the options

• A. Anemometer: measures wind speed.
• B. Barometer: measures atmospheric pressure.
• C. Hydrometer: measures the density (specific gravity) of liquids.
• D. Photomer: not a standard biology instrument. It looks like a distractor made from "photo-" (light).
• E. Potometer: measures the rate of water uptake by a cut leafy shoot, which is used to estimate the rate of transpiration.

Step 3: Explain the concept A potometer is a glass apparatus with a capillary tube. A leafy shoot is fixed into it, and an air bubble is introduced into the capillary tube. As the plant transpires, it draws water up, and the air bubble moves along the scale. The distance the bubble travels in a set time gives the rate of water uptake, which is closely related to the rate of transpiration.

Note that the potometer technically measures water uptake, and nearly all of that water is lost through transpiration. That is why it is the standard instrument for this purpose.

Step 4: Answer The correct option is E. Potometer.

Exam tip: Match the name to its function. "Poto" resembles "pot" or "potable" (water), so a potometer deals with water uptake in plants. Also remember that an anemometer measures wind, a barometer measures pressure, and a hydrometer measures liquid density. Factors that increase transpiration, such as wind, high temperature, low humidity, and light, are often tested alongside this question.