Gas Exchange In Plants Flashcards
How do plants respire?
Aerobically with oxygen. They use oxygen and produce carbon dioxide it happens in the mitochondria.
Photosynthesis?
In the daylight they also photosynthesise which requires carbon dioxide and produces oxygen.
What does a balance of respiration and photosynthesis allow?
A balance of the two maintains the concentration gradient.
Where does gas exchange occur in plants?
Gas exchange occurs on the surface of the palisade and spongy mesophyll cells which are in contact with air spaces inside the leaf creating a short diffusion pathway. It also takes place in gas phases so is fast. The leaf is thin and wide therefore surface area to volume is large. No cell is ever far away from air.
What do the numerous stomata do?
They also have numerous stomata to allow air to diffuse. Most stomata are underneath the leaf. A stomata is surrounded by 2 guard cells these control the opening and closing which controls the diffusion of gas and water vapour. Plants have to balance the loss of water with gas exchange. The stomata is open when guard cells are turgid and when it’s closed the guard cells are flaccid.
What must plants do to survive?
They must conserve water without limiting the efficiency of the gas exchange system. These are conflicting needs of an efficient gas exchange system and the need to conserve water, the things that make a good exchange system increase water loss.
Main ways of limiting water loss?
While plants have a waterproof covering they have a large SA:V for photosynthesis, to reduce water loss they also have the ability to close the stomata when necessary. Certain plants with restricted water supplies have evolved to limit water loss through transpiration, these are called xerophytes.
Plants also have many other modifications to reduce the rate of water loss such as?
- a thick cuticle, 10% water loss occurs via the waxy cuticle, the thicker it is the less water that is lost.
- hairy leaves which trap moist air next to the leaf surface so the WP is reduced inside so less is lost.
- stomata in pits or grooves which traps moist air.
- a reduces SA:V of the leaves by having a small circular leaves e.g. pine needles reduces the rare of water lost, the reduced SA is balanced against the need for sufficient area for photosynthesis.
- the rolling up of leaves which protects the lower epidermis where the stomata usually is and traps a region of still air within it. The region becomes saturated and has a high WP, there is no gradient so none lost.
