6.4 and 6.5 Gas exchange in the leaf of a plant and reducing water loss Flashcards
What is the gas exchange for respiration of a plant cell
What about for photosynthesis
They take in oxygen and release carbon dioxide
The cells that are doing photosynthesis take in carbon dioxide and release oxygen
Why is it good that photosynthesis and respiration occur at the same time
The oxygen released from photosynthesis can be used for respiration.
This reduces gas exchange with the environment
How is gas exchange in plants similar to gas exchange in insects
(short diffusion pathway)
. No living cell is far from the external air so is therefore close to a source of oxygen and carbon dioxide
. Diffusion takes place in the gas phase (air) which makes it more rapid than if it were in water
So there is a short diffusion pathway
How do leaves have a large surface area to volume ratio
The air spaces inside leaves have a large surface area compared to the volume of living tissue
Where does most gas exchange occur in plants
In leaves
How do gases move in and out of the plant
There is no specific transport system so the gases move in and out by diffusion directly
They enter and leave through the stomata
What are the adaptations of leaves for gas exchange
. They contain many small pores called stomata where gases can diffuse in and out.
No cell is far from a stomata so the diffusion pathway is short.
. Large surface area of mesophyll cells for rapid diffusion
. Numerous interconnecting air spaces that occur throughout the mesophyll so gases can readily come in contact with mesophyll cells that could be photosynthesising or respiring
What are stomata and what are they controlled by
Mini pores that are mainly found in leaves, especially on the underside of them
Two guard cells are on either side of each stoma and they can control when to open and close each stomatal pore
Why is it good for plants to have stomata
They can control the rate of water loss by evaporation in terrestrial organisms.
They help to balance the conflicting needs of gas exchange and water loss by being able to close at times when water loss would be excessive
Describe the layers in leaves
. Upper epidermis
. Palisade mesophyll containing chloroplasts for photosynthesis
. Spongy mesophyll where gas exchange can occur through all the gaps in it
. Lower epidermis containing stomata and guard cells
Majority of water loss occurs through leaves
Name the 5 adaptations do leaves have to help reduce this
. Thick waxy cuticle layer
. Rolling up leaves
. Stomata in pits or grooves
. Hairy leaves
. A reduced surface area to volume ratio in leaves
How does having a thick waxy cuticle layer reduce water loss in plants
Thick waxy cuticle layer can form a waterproof barrier, however up to 10% of water loss can occur through this route
Thicker the cuticle, the less water that can escape. Eg in Holly
How does rolling up leaves reduce water loss in plants
. Most leaves have their stomata mainly on the lower epidermis.
Leaves can roll up to protect these stomata from the outside which can trap a region of still air within the rolled up leaf
. This region can become very saturated with water vapour so has a high water potential
This means there is no water potential gradient between the inside and outside of leaf so therefore there is no water loss
Eg Marram leaves
How do hairy leaves reduce water loss of plants
Thick layer of hairs, especially on lower epidermis can trap a layer of moist air next to the leaf surface
This reduces the water potential gradient between the inside and outside of leaf so there is much less loss of water
Eg heather plants
How do the stomata in pits and grooves of leaves reduce water loss
These trap still, moist air next to them which reduces the water potential gradient between the inside and outside of leaf so less water is loss by evaporation
Eg pine trees
How does a reduced surface area to volume ratio in the leaves reduce water loss
Name examples of plants
The smaller the surface area to volume ratio, the lower the rate of diffusion
So having small and circular leaves eg pine needles, rather than big and flat leaves can reduce the rate of water loss
You need to balance this with the need in surface area for sunlight for photosynthesis
What are xerophytes
Plants that are adapted to live in areas where water is in short supply, they may show a large range of desert adaptations eg in hot and dry conditions
Why should water loss limited in insects
Most insects are terrestrial so live on land which means there is a problem of water evaporating from their surface and they can become dehydrated
Insects have to balance the conflicting needs for a good gas exchange system, whilst reducing water loss
What adaptations do insects have that reduce water loss
And what does this mean for gas exchange of insects
- Small surface area to volume ratio to minimise the area over which water is lost
- Waterproof coverings over the body surfaces eg having a rigid outer skeleton of chitin that is covered with a waterproof cuticle
- Spiracles are the openings to the trachea at the body surfaces and they can be closed to reduce water loss. This conflicts with the need for oxygen so occurs largely when the insect is at rest
This means that gas exchange by diffusion can’t occur so they have to use their trachea to carry oxygen to the tissues
Why do plants not usually have a small surface area to volume ratio
They rely on photosynthesis for energy which means there has to be a large surface area for the chloroplasts to absorb the maximum amount of sunlight
