Gas Exchange in Plants Flashcards
Properties of gas exchange
- Large surface area
- Thin (one layer of epithelial cells) - provide short diffusion pathway across gas exchange surface
What does the organism do for gases across exchange surface?
Maintain concentration gradient
How does single-celled organisms utilise diffusion?
Absorb and release gases by diffusion through their outer surface
Why does single-celled organisms not need gas exchange?
- Large surface area
- Short diffusion pathway
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Why do plants need O2?
For respiration
produces CO2 as a waste product
What is the main gas exchange surface for leaf?
Surface of mesophyll cells in leaf
-well adapted for their function
Large surface area
How do gases move in mesophyll cells?
They are found inside the cells
Gases move in and out of pores in epidermis called stomata
What can stomata control?
They can open to allow exchange of gases and close if the plant is losing too much later
Guard cells control the opening and closing of stomata
What is the unfortunate consequence of exchanging gases?
Lose water
How are insects specialised if they are losing too much water through exchanging gases?
- They close their spiracles using muscles
- Waterproof waxy cuticles all around body and tiny hairs around spiracles to reduce evaporation
Are plants stomata open during gas exchange?
Yes
How does water enter through plants stomata?
Water entering guard cells making them turgrid which opens stomatal pore
What happens if the plant is dehydrated with gas exchange?
If plants start to dehydrate, the guard cells lose water and become flaccid - close pore
What plants is this a problem for water loss?
Xerophytes- plants live in dry/windy habitats
Following adaptations for xerophytic plants
- Stomata
- Layer of hairs on epidmeris
- Curled leaves
- Reduced number of stomata
- Waxy , waterproof cuticles
How is stomata adapted for xerophytic plants?
Sunk in pits trap moist air - reducing concentration gradient of water between leaf and air
Reduce the amount of water diffusing out of the leaf and evaporating away
How is their layer of hair around epidermis adapted for xerophytic plants?
Trap moist air around the stomata
How is curled leaves with stomata inside the xerophytic plants adapted?
Protecting them from wind
windy conditions increase rate of diffusion and evaporation
How is the reduced number of stomata adapted for xerophytic plants?
Fewer places for water to escape
How having waxy, waterproof cuticles on leaves adapted for xerophytic plants?
reduce evaporation
Species C has a high number of stomata per mm2
Despite this it loses a small amount of water
Use this data to explain why:
It is thick so huge diffusion distance pathway
Suggest an appropriate units the student should use to compare the distribution of stomata on leaves
Stomata per millimetre per squared
The pieces of leaf were very thin. Explain why this was important.
This allows the light to pass through
This means you can view it properly under the optical microscope
Give two reasons why it was important to count the number of stomata in several parts of each pieces of leaf tissue
- Very accurate
- It won’t be the same number of stomata
Suggest two reasons why the rate of water uptake by plants might not be the same as the rate of transpiration
- Water used in photosynthesis
- Water is produced in respiration
Treatment 2 shows that even when the lower surface of the leaf is sealed there is still some uptake of carbon dioxide
Suggest how this uptake of carbon dioxide continues
CO2 uptake through the upper surface
In both treatment 1 and 2 , the uptake of carbon dioxide falls to zero when the light is turned off
CO2 used in photosynthesis
it is not anymore
What happens when the plant has a lot of H20?
Guard cells are turgid
State the two similarities between gas exchange in plants leaf and gas exchange in an insect
- Diffusion takes place in gas phase
- Need to avoid excessive water loss
State two differences between gas exchange in leaf and insect
- Insects has smaller surface area to volume raito
- Insects do not interchange gases between respiration and photosynthesis - plants do
- Insects has trachae along which gases diffuse - plants do not
Explain the advantage of a plant of being able to control the opening and closing of the stomata
Helps to control the water loss by evaporation/transpiration
