Transpiration — Part 2: Potometer, factors, guttation: visual lesson, ICSE Class 10 Biology (Science Paper 3)

Lesson

Measuring and Controlling Water Loss

Part 2 — the potometer, what speeds transpiration up or slows it down, and other ways plants lose water.

In this lesson you will

Explain how Ganong's potometer measures water uptake and state its limitations
Predict the effect of light, temperature, humidity and wind, and describe adaptations that reduce water loss
Distinguish guttation from transpiration and from bleeding

Diagram

Ganong's potometer

A leafy shoot in an airtight, water-filled apparatus; as it takes up water, an air bubble moves along a graduated capillary towards the shoot.

Concept

Using the potometer

Table of steps in using a potometer and the reason for each
Step	Reason
Cut the shoot under water	Keeps air out of the xylem
Seal all joints with Vaseline	Keeps the apparatus airtight
Let in one air bubble	Marks the movement of water
Time the bubble over a fixed distance	Gives the rate of water uptake
Open the reservoir stopcock	Pushes the bubble back to the start

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