Potometers

You need to measure the rate of transpiration in a leaf shoot. You should use...

• A ruler

• A balance

• A potometer

• A syringe

What is the purpose of the valve shown by the arrow?

• Lets you move the air bubble back to the start of the scale for the next test

• Lets you remove the water

• Transpiration is measured here

• You can add a second leafy shoot here

When assembling a potometer you should...

• Cut the leaft shoot and assemble under water

• Ensure there are no leaks where the stem joins the tube

• Briefly lift the end of the capillary tube above the water to introduce an air bubble

• Assemble the potometer on the bench

To work out the rate of transpiration using the potometer you need to know...

• The time taken

• The distance the bubble moves along the scale

• The area of the end of the capillary tube

• The species of plant

If you were using a potometer to compare rate of transpiration of two species of plant, which factors should you try to control?

• age of plant

• species of plant

• number of leaves on plant

• type of potometer used

Which conditions tended to give the highest rate of transpiration in our potometer experiments?

• high light intensity

• high temperature

• high wind speed

• high humidity

high temperature increases transpiration rate because...

• at high temperature water evaporates faster inside the leaf

• at high temperature particles have more KE

• diffusion happens faster at higher temperatures

High light intensity tends to increase transpiration rate because...

• Stomata open in bright conditions

• diffusion is faster in bright conditions

High wind speed causes a greater rate of transpiration because...

• The wind removes water vapour from the air around the leaves maintaining the concentration gradient for diffusion

• wind gives the gases in the air more KE

• water vapour can get blown back inside the leaves through the stomata

If we used grease to cover one surface of a leaf, which greased surface would cause the greatest reduction in transpiration rate?

• Upper surface

• Lower surface