Transpiration

Question 1

Define Transpiration

Answer 1

The evaporation of water vapour a plant’s surface.

Question 2

How does light intensity effect the rate of transpiration?

Answer 2

Higher light intensity = Faster rate of transpiration

Stomata open when there’s light, so that CO2 can diffuse into the leaf for photosynthesis

When it’s dark, stomata close so there is little transpiratio

Question 3

How does temperature effect the rate of transpiration?

Answer 3

Higher temp = faster rate of transpiration

More kinetic energy so water molecules evaporate quicker

This increases the water potential gradient between the inside and outside of the leaf, making the water vapour diffuse faster

Question 4

How does humidity effect the rate of transpiration?

Answer 4

Lower humidity = faster transpiration

when the air around the plant is dry, the water potential gradient between the air and the leaf is increased, so there is more transpiration

Question 5

How does air movement/wind effect the rate of transpiration?

Answer 5

More wind = faster transpiration

Air movement blows water molecules away from stomata, which increases the water potential gradient, increasing the rate of transpiration

Question 6

What do potometers measure?

Answer 6

Water uptake by a plant

Question 7

When preparing a plant for a potometer, why do you cut the stem underwater?

Answer 7

So that air doesn’t enter the xylem

Question 8

Where are xerophytes located?

Answer 8

Dry conditions

Question 9

Adaptions of marram grass to reduce transpiration

Answer 9

Sunken stomata - sheltered from wind

Layer of hairs on the epidermis - traps moist air which reduces the water potential gradient between the leaf and the air which slows transpiration

Rolled leaves - traps moist air, slowing transpiration and reducing the exposed surface area

Question 10

Adaptions of cacti to reduce transpiration

Answer 10

Spines instead of leaves - reduces surface area

Closed stomata at hot times of the day

Question 11

Where are hydrophytes located?

Answer 11

Aquatic environments

Question 12

Adaptions of hydrophytes

Answer 12

Air spaces in tissues - helps plant float

Stomata only on upper surface - maximise gas exchange

Flexible leaves and stems - support and to prevent damage by water currents

Question 13

Where does water move in an apoplast pathway?

Answer 13

cell walls

Question 14

Why does the apoplast pathway have to switch to the symplast pathway?

Answer 14

The casparian strip in the endodermis is thick, waterproof and waxy

Question 15

Where does water move in a symplast pathway?

Answer 15

Through cytoplasm and plasmodesmata

Question 16

Explain the cohesion-tension theory

Answer 16

The movement of water through the xylem is due to the evaporation of water vapour from the leaves and the cohesive and adhesive properties of water molecules

Question 17

Why does the transpiration stream occur?

Answer 17

The water potential gradient inside to outside the leaf means that water vapour moves out of the leaf

this lowers the water potential gradient in the air spaces around mesophyll cells

The water in these mesophyll cells evaporates into air spaces - creating transpiration pull

Water moves through the mesophyll cell wall or the mesophyll cytoplasm into the cell wall

This results in water leaving the xylem vessels through the pits, which causes water to move upwards.