Using a Potometer Flashcards

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What is a potometer used for in plant experiments?

It is used to measure the rate of water uptake by a plant shoot, as an estimate of the rate of transpiration.

Why does a potometer only give an estimate of the transpiration rate?

Because not all water taken up by the plant is lost by transpiration; some is used in the leaves for support and in chemical reactions.

Name three main parts of a simple potometer.

A water-filled capillary tube with a scale, a reservoir, and a leafy plant shoot joined with airtight tubing.

Why must the plant shoot be cut under water when setting up a potometer?

Cutting the shoot under water stops air entering the xylem vessels, which would block water flow and give false results.

How do you introduce an air bubble into the capillary tube of a potometer?

Lift the end of the capillary tube briefly out of the water so air enters, then place it back under water to trap a single bubble.

How do you use the air bubble to find the rate of water uptake?

Measure how far the bubble moves along the scale in a known time, then calculate rate = distance moved ÷ time taken.

How can you reset the potometer between readings?

Open the reservoir tap or squeeze the reservoir so water pushes the air bubble back to the start point on the scale.

Why must all joints in a potometer be sealed and watertight?

So that water loss only happens through the plant. Leaks would let in air or lose water, which would change the bubble movement and the results.

When using a potometer to test one factor, what should you do with the other conditions?

Keep other conditions the same, such as temperature, wind, humidity, and light, so only the factor you change affects the rate.

Describe one way you could use a potometer to study the effect of light intensity.

Place the potometer at different distances from a lamp to give different light levels, measure bubble movement each time, and compare the rates of water uptake.