Gas exchange in plants

Question 1

What is the role of diffusion in gas exchange (in multicellular organisms)

Answer 1

Diffusion occurs on exchange surfaces and organ systems e.g. leaves, roots
Efficiency of diffusion is increased by organs having a large surface area, short diffusion distance and gas exchange surfaces that are well ventilated to maintain steep concentration gradients

Question 2

Gas exchange during photosynthesis

Answer 2

Plant cells photosynthesize when there is enough sunlight, requiring uptake of CO2 and the release of oxygen
- The carbon dioxide diffuses down the concentration gradient from outside the leaf to inside the leaf
! The cells use carbon dioxide for photosynthesis so the concentration is always low inside the cells
- The oxygen diffuses down the concentration gradient from inside the leaf to outside the leaf

Question 3

Gas exchange during respiration

Answer 3

Plant cells respire, requiring uptake of oxygen and the release of CO2
- The oxygen diffuses down the concentration gradient from outside the leaf to inside the leaf
! The cells use oxygen for respiration so the concentration is always low inside the cells
- The carbon dioxide diffuses down the concentration gradient from inside the leaf to outside the leaf

Question 4

Leaf adaptations for gas exchange

Answer 4

Thin - short diffusion distance; and flat - large SA:V ratio
Many stomata which allow movement of gases in and out of the leaf to maintain a steep concentration gradient

Question 5

Function of stomata:

Answer 5

Stomata are spaces found between two guard cells predominantly on the lower epidermis of the leaf
Stomata open: When guard cells are turgid - allows gases to diffuse in and out of the leaf (when there is water and sunlight)
Stomata closed: When guard cells are flaccid - prevents diffusion in our out of the leaf (when there is little water or sunlight)

Question 6

During the daytime plants:

Answer 6

Respire and photosynthesize
- Rate of photosynthesis is higher than the rate of respiration
- Net diffusion of CO2 into the plant, net diffusion of O2 out of the plant

Question 7

During the nighttime plants:

Answer 7

Only respire
-Net diffusion of O2 into the plant, net diffusion of CO2 out of the plant

Question 8

At low light intensities:

Answer 8

The rate of photosynthesis is equal to the rate of the rate of respiration
- No net movement of O2 or CO2 in either direction