1. Transpiration
Lesson 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
2. 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?
3. Transpiration
Transpiration 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.
4.
5. 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?
6. Transpiration
• Sort the statements out into the correct order
to show how water moves to the top of the
plant
7. Transpiration
Experiment Distance bubble moved after each minute in mm
Time in
1 2 3 4 5 6 7 8 9 10
min
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
8. Is the rate of transpiration constant?
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.
The speed at which a plant loses water is called
the rate of transpiration.
What environmental factors will affect
the rate of transpiration?
humidity (amount of moisture in the air)
light intensity
temperature
air movement (wind).
9.
10. 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
Teacher notes This four-stage animation uses close-up illustrations of the roots, stem and leaves to show what happens in the different part of a plant during transpiration. Suitable prompts include: Start: What is transpiration? Stage 1: How do root hair cells increase the diffusion of water? Stage 2: Which plant tissue transports water? Stage 3: Through what part of the leaf does water evaporats? Stage 4: What will happen to the water after it has evaporated into the air? See the ‘ Movement In and Out of Cells ’ presentation for more information about osmosis and concentration gradients.
Teacher notes This activity provides illustrated explanations about why certain environmental factors influence the rate of transpiration. It could be used to introduce the topic or for revision purposes.
