Lecture notes
GCSE/iGCSE biology plant gas exchange
GCSE/iGCSE biology plant gas exchange. Allowed me to achieve a 9 in my exam. Very helpful, over 50 questions and answers
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What are adaptations of leaves for gas exchange? Air spaces in spongymesophyll - reduce diffusion pathway of gases like carbon dioxide and oxygen
Stomata allow gases to enter and exit the leaf
Guard cells control movement of gases into and out of the leaf
Which substances diffuse in and out of plants through the stomata? Oxygen and
carbon dioxide
How do stoma open and close? If the guard cells are flaccid or turgid. Water moves
in to the cells via osmosis
Which cells regulate stomatal opening? Guard cells
Why are stomata mainly on the underside of a leaf? To prevent uncontrolled water
loss due to evaporation
How would the density of stomata change in plants that are adapted to dry
conditions compared to plants in more temperate conditions?Reduced density to
minimise water loss via evaporation
What are the differences between the palisade mesophyll and the spongy mesophyll?
Palisade mesophyll:
Closely packed together just beneath the upper epidermis.
Contains lots of chloroplasts to absorb sunlight for photosynthesis
Spongy mesophyll:
Have air spaces to allow diffusion of gases into and out of the leaf
Located in middle layer of leaf
What does the waxy cuticle do? Reduces water loss by evaporation
Why are there no stomata on the outer surface of the leaf? Minimises water loss
because the outside of the leaf is exposed to sunlight and more prone to
evaporation
What is the function of the hairs on the inner surface of the leaves? Reduces air
flow
Increases humidity
Reduces diffusion
Reduces water loss
How will sunken stomata affect gaseous exchange? Sunken stomata will mean
there will be reduced water loss due to increased humidity
Therefore stomata remain open
Therefore gaseous exchange will increase
Allowing photosynthesis despite limited water supply
Describe an experiment to investigate the effect of light on gas exchange by a leaf
using hydrogencarbonate indicator. 1. Place 10cm^3 of hydrogencarbonate indicator
soution into the bottom of all 4 boiling tubes
2. Place 3 large green leaves into the top of three of the tubes
3. Seal each tube with a bung
4. Place one tube in a bright light, one in the dark covered in silver foil, and
the third tube in tissue paper to restrict the light intensity reaching the leaf.
The fourth tube will act as a control
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