Organisms Exchange Substances with their Environment: Gas Exchange - Plants

Question 1

Which gases do plants need and which processes are these gases used in?

Answer 1

• Plants need carbon dioxide for photosynthesis, which produces oxygen as a waste gas
• Plants need oxygen for respiration, which produces carbon dioxide as a waste gas

Question 2

What is the main gas exchange surface in leaves?

Answer 2

• The main gas exchange surface is the surface of the mesophyll cells in the leaf

Question 3

What are mesophyll cells?

Answer 3

• Cells where photosynthesis occurs

Question 4

What are stomata?

Answer 4

• There are many pores in the epidermis (mostly lower) called stomata
• They open to allow gas exchange of gases
• Close if plant is losing too much water
• Guard cells control the opening and closing of stomata

Question 5

How are the leaves of plants adapted to carry out gas exchange?

Answer 5

• Thin and flat

• Provides short diffusion pathway
• Large SA:V

• Many stomata

• Allows gases to easily enter
• Large surface area
• Means no cell is far from stomata - short diffusion pathway

• Air spaces in mesophyll
- Allows gases to move around leaf to photosynthesising mesophyll cells

Question 6

How do plants limit their water loss while still allowing gases to be exchanged?

Answer 6

• Stomata regulated by guard cells
• Which allows them to open and close as needed
• Most stay closed to prevent water loss, while some open to let oxygen in

Question 7

Describe the relationship between gas exchange and water loss

Answer 7

• Exchanging gases tends to make you lose water

- Plants have evolved adaptations to minimise water loss without reducing gas exchange too much

Question 8

What are xerophytes?

Answer 8

• Plants that are specially adapted for life in warm, dry or windy habitats where water loss is an issue

Question 9

How are xerophytes adapted to reduce water loss?

Answer 9

• Sunken stomata

• Sunk in pits to trap water vapour, reducing concentration gradient of water between leaf and air
• This reduces rate of transpiration

• Hairs
- Layer of hairs to trap water vapour on the epidermis

• Curled leaves

• Keeps stomata inside leaf, protecting them from wind
• Reduces rate of transpiration

• Reduced number of stomata

• Fewer places for water to escape
• Reduces surface area and therefore rate of diffusion

• Thick, waxy, waterproof cuticles

• Wax is impermeable to water
• Thick - increases diffusion distance