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
Many stomata: no mesophyll cell is far from a stoma so diffusion pathways are short
Many large air spaces in the spongy mesophyll to increase the surface area of contact between the air and cells.
Leaf is thin to keep the diffusion pathways short
How the stomata can open and close: 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 adapted to live in warm, windy or dry habitats where they receive little liquid water
Xerophyte adaptations
Sunken stomata
Layer of hairs on epidermis
Rolled leaves
Spine shaped leaves
Less stomata
THICKER Waxy cuticle
How sunken stomata prevents water loss
Stomata sunk in pits to trap water vapour in air near the stomata
Reduces water potential gradient between cell and outside
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 reduced water potential gradient
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
And water is trapped near stomata so decreases water potential gradient
How less stomata reduces water loss
Fewer places for water to escape
How THICKER waxy cuticles prevent water loss
Reduces evaporation due to waterproofing but because its thicker, increases diffusion distance
dicotyledonous
Plants thats embryo plant in the seeds has 2 leaves
How are epidermis cells adapted for gas exchange?
Transparent to allow light to pass through to mesophyll cells for photosynthesis
SO no chloroplasts = no photosynthesis
Secretes waxy cuticle = waterproofing to reduce water loss
During the day for plants…
Both respiring and photosynthesising through open stomata
Rate of photosynthesis > respiration
= net uptake of CO2 into leaf and O2 out
During the night for plants…
No photosynthesis
Only respiration of glucose that has been produced during the day so net uptake of O2 used in the cell and CO2 lost from cell
Name for evaporation of water out of stomata of a cell
Transpiration
When do plants close stomata?
Night: no photosynthesis so not much point having it open
When plant doesnt have enough water to reduce water loss
Why does closing the stomata reduce plant growth?
Not enough CO2 can enter plant = not enough photosynthesis so less glucose is produced = reduced growth
How do spine shaped leaves in a xerophyte decrease water loss?
Decreases surface area to volume ratio so less water can evaporate from stomata at once
