Gas Exchange - Plants

Question 1

Where does carbon dioxide travel in the leaf?

Answer 1

• CO2 diffuses into the stoma and travels into the spongy mesophyll which has lots of spaces for the gasses to diffuse and helps maintain a conc gradient
• CO2 can then diffuse to the palisade mesophyll where most photosynthesis occurs

Question 2

How is the leaf adapted for efficient gas exchange?

Answer 2

• lots of stomata = short diffusion pathway
• numerous air spaces throughout the mesophyll so that gases can come into contact with the mesophyll cells
• large SA of mesophyll for rapid diffusion

Question 2

What are xerophytes?

Answer 2

plants adapted to live in areas where there is shortage of fresh water

Question 3

What is the movement of water like via the stomata?

Answer 3

• normally humidity of the atmosphere is less than the air surrounding the stomata which creates a water potential gradient
• if open water will move diffuse out of air spaces into surrounding air and water lost is replaced by water evaporating from cell wall of mesophyll cells
• these cells now have lowered water potential do water enters by osmosis from neighboring cells → pulls water from xylem across mesophyll to atmosphere

Question 4

How are xerophytes adapted for gas exchange?

Answer 4

• curled up leaves → traps still air which has become saturated with water vapour, reducing water loss
• hairy leaves → traps still moist air reducing water potential gradient
• thick cuticle → waxy cuticle forms waterproof barrier and reduces evaporation
• sunken stomata (in grooves) → traps till moist air
• all adaptations trap moisture to increase local humidity

Question 5

What is the movement of gases via the stomata?

Answer 5

• oxygen diffuses out of the stomata
• carbon dioxide diffuses in through the stomata