Gas exchange in plants Flashcards
Layers of a leaf fell from top to bottom
Waxy cuticle
Upper epidermis
Palisade mesophyll cells
Spongy mesophyll cells
Lower epidermis: guard cells
Waxy cuticle + stomata
Main gas exchange site in plants
Mesophyll cells
Gas exchange in a plant cell
CO2 diffuses in (needed for photosynthesis)
O2 diffuses our (waste product of photosynthesis)
O2 diffuses in (respiration needed)
CO2 diffuses out (waste product of photosynthesis
How do gases move into the leaf?
Through pores on the under side of leaf called stomata
What controls the opening of stomata?
Guard cells
When do guard cells open the stomata?
To allow diffusion of gases inside:
During the Day only for photosynthesis (only when sun is out) and respiration
When do guard cells close the stomata?
Reduce water loss
Adaptations of plants for gas exchange
Large surface area of mesophyll to maximise the amount of gas exchange happening at once
Air spaces so gases don’t have to diffuse through cells to get where they’re needed (shorter diffusion distance)
How the stomata controls water loss
Water enters guard cells causing it to become turgid and open the stomata pore, this is because the leaf isn’t dehydrated due to water moving in
Once plant is dehydrated, the water leaves guard cells thus stomata closes
Xerophytes
Plants that are damaged to live in warm, windy or dry habitats where water loss is a problem
Xerophyte adaptations
Sunken stomata
Layer of hairs on epidermis
Curlew leaves
Less stomata
Waxy cuticle
How sunken stomata prevents water loss
Stomata sunk in pits to trap water vapour in air near the stomata
Creates concentration gradient of trapped water in the air higher than in the cell
So water doesn’t evaporate against its concentration gradient out of the leaf
How layer of hairs reduces water loss
On the epidermis which traps water around the stomata so the concentration of water in air is higher outside the leaf than insides prevents water evaporating out the leaf against the concentration gradient
How curled leaves prevent water loss
The stomata is protected from the wind
So rate of evaporation is decreased, as wind increases rate of evaporation
How less stomata reduces water loss
Fewer places for water to escape
