Transpiration

Question 1

Explain how light affects transpiration rate

Answer 1

• The lighter it is, the faster the transpiration rate
• The stomata open when it gets light, so CO2 can diffuse into the leaf for photosynthesis, and this lets water out down the water potential gradient. They close when its dark, so there is little transpiration.

Question 2

Explain how temperature affects transpiration rate

Answer 2

• the higher the temp, the faster the transpiration rate
• warmer water molecules have more energy so evaporate from the cells inside the leaf faster. This then increases the water potential gradient between the inside and outside of the leaf, making water diffuse out the leaf faster

Question 3

Explain how humidity affects transpiration rate

Answer 3

• the lower the humidity, the faster the transpiration rate
• if the air around the plant is dry, the water potential gradient between the leaf and the air is increased, increasing transpiration

Question 4

Explain how wind affects transpiration rate

Answer 4

• the windier it is, the faster the transpiration rate
• lots of air movement blows away water molecules from around the stoma, increasing water potential gradient, increasing transpiration rate

Question 5

What are xerophytic plants? Give an example

Answer 5

• Ones adapted to live in extreme dry climates, where water availability is low
• cacti

Question 6

Explain some ways in which xerophytic plants have adapted to prevent them losing too much water by transpiration.

Answer 6

1) Thick waxy cuticles= minimises water loss by transpiration because this layer is waterproof and water can’t move through it
2) sunken stomata in pits= shelters them from wind, reducing water potential gradient and transpiration
3) reduced numbers of stomata= reduces gas exchange capabilities and therefore water loss by transpiration
4) hairy leaves= traps moist air around the stomata, reducing water potential gradient and transpiration

Question 7

What are hydrophilic plants? Give an example

Answer 7

• plants that live in aquatic environments, that are adapted to cope with low oxygen levels
• water lilies

Question 8

Explain some ways in which hydrophilic plant have adapted to help them cope in low oxygen levels and survive in the water

Answer 8

1) air spaces in tissues= help them float on surfaces of water, increasing the amount of light they receive and increasing photosynthesis and also allow for oxygen to move into the air spaces of roots and stems under water.
2) stomata only present on upper surface of floating leaves= maximises gas exchange
3) very thin or no waxy cuticle= don’t need to conserve water so it can be lost by transpiration