How does carbon dioxide enter and oxygen go out of the leaves ?
On the under-side of leaves there are tiny holes called stomata
Special guard cells are responsible for opening and closing stomata
How does the water get into plants?
Water is absorbed through root hair cells by osmosis
In osmosis water moves from an area of high water concentration to a region of low water concentration
A root hair cell has a large surface area and thin walls to help water uptake
Selectively permeable membrane
Why is water needed in plants?
Water is required for photosynthesis
Water is needed to maintain turgidity i.e. to keep plants cells rigid and to stop them from losing their shape and going flaccid (floppy)
Evaporation of water through stomata cools the plant down on a hot day
Xylem tissue is made up of dead cells joined end to end (with no ‘end walls’)
Xylem tubes contain lignin which makes them strong and stiff
Xylem tubes take water up the plant, along with mineral salts dissolved in the water
Phloem tubes are made of living cells with perforated end-plates (to let substances pass through)
Phloem tubes transport food made in the leaves to all other parts of the plant
Substances such as starch, fats and proteins are carried by phloem to the growing shoot tips and root tips, and to storage organs in the roots
Phloem can transport food in both directions
A cross-section through a stem, stained to show the phloem and xylem vessels
What else can get out of leaves through the stomata?
Water is lost through the stomata during transpiration
Transpiration is the constant flow of water up the plant
It is caused by the evaporation of water from the plant through the stomata