Transpiration

Where does photosynthesis take place in the plant?

Photosynthesis takes place in the palisade mesophyll.

What does xylem tissue do?

Xylem tissue transports water and dissolved mineral ions from the roots to the leaves.

How does water enter the roots?

Via root hair cells.

What is transpiration?

Water is constantly evaporating from the surface of leaves.

What is the first stage of transpiration?

Water evaporates from the cells inside the leaf.

What happens after water evaporates from cells inside the leaf?

The water vapour diffuses through the air spaces in spongy mesophyll and exits through the stomata.

What is the transpiration stream?

• Water passes from the xylem into the leaf to replace the water that has been lost.

• Water is drawn into root hair cells and up the xylem vessels to the leaf.

Why is transpiration so important?

• It brings water to the leaf, which is required for photosynthesis.

• Transports dissolved mineral ions such as magnesium, which plays important roles in the plant.

What does evaporation of water from the leaf do?

Cools the leaf down, especially in warm weather.

At what temperatures is the rate of transpiration higher?

Higher temperatures cause greater rates of transpiration.

Evaporation is faster when temperatures are higher.

What humidity is transpiration fastest?

In dry conditions, when it is not very humid.

Evaporation is quicker in dry conditions.

What sort of wind conditions is transpiration greatest in?

Rate of transpiration increases in windy conditions.

Wind removes any water vapour, allowing more to evaporate.

What light intensity does transpiration happen the fastest?

Rate of transpiration increases when light intensity increases.

High light intensity increases rate of photosynthesis.

Why does increased rate of photosynthesis increase rate of transpiration?

Because the stomata opens to allow carbon dioxide to enter meaning water vapour can pass out of the leaf.

What are stomata surrounded by?

2 guard cells.

What happens to guard cells when light intensity is high?

The guard cells swell and change their shape.

This causes the stomata to open.

What happens once the stomata is open?

Carbon dioxide can diffuse into the leaf and be used in photosynthesis.

What happens to stomata in hot conditions?

It closes to reduce water loss by transpiration. BUT this means the plant cannot photosynthesise.