TranspirationLesson objectives

• All will be able to describe transpiration

• Most will be able to explain differences in transpiration speed

• Some will suggest reasons why plants compromise between gas exchange and water loss

How do tall trees get enough water?

Redwoods are the tallest species of tree in the world - the tallest was 120 metres.

How does a plant this size get water from its roots to the branches at the top?

What experiment could show that water travels up stems?

TranspirationTranspiration can be measured using a potometer.

A cut plant stem is sealed into the potometer using a rubber bung.

An air bubble is introduced to the capillary tube.

The distance the bubble travels shows how much water the stem has taken up.

1. Record a definition of transpiration

2. Where do plants lose water?

3. Transpiration will often lead to water loss by the plant so what is its purpose and what is the major advantage?

Transpiration

• Sort the statements out into the correct order to show how water moves to the top of the plant

TranspirationExperiment Distance bubble moved after each minute in mm

Time in min

1 2 3 4 5 6 7 8 9 10

A 2 3 5 7 10 11 13 15 18 20

B 13 24 38 49 73 75 89 114 118 152

C 5 12 18 24 30 35 41 47 53 58

humidity (amount of moisture in the air)

Is the rate of transpiration constant?

The speed at which a plant loses water is called the rate of transpiration.

Transpiration is a bit like a straw, pulling water up the plant. Sometimes the pulling force will be stronger and the plant will lose more water.

What environmental factors will affect the rate of transpiration?

light intensity

temperature

air movement (wind).

How does a plant control water loss?

1. Waxy waterproof layer (cuticle)

2. Stomata on the underside of the leaf (not expose to sun)

3. Wilting. Leaves collapse reducing surface area

4. Stomata close