1. Leaf Structure

2. Functions of Leaves Main photosynthetic organ
Broad, flat surface increases surface area for light absorption
Have systems to prevent water loss
Stomata open in day but close at night or when hot to conserve water
waxy cuticle on surface
System of gas exchange
Allow CO2 in and O2 out of leaf
Elephant Ear Plant

3. Structure of a leaf
Waxy cuticle – waterproof layer (reduces water loss from surface)
Veins (stands of xylem and phloem from midrib)
Form a bundle of vascular tissue
xylem
Stomata – pores on underside of leaf through which carbon dioxide and water vapour are exchanged
phloem
Midrib (vascular tissue i.e. phloem and xylem)
Leaf stalk (petiole)
Stem
(supports plant)

4. Section through a leaf Upper side of leaf lower side of leaf
waxy cuticle to prevent water loss
Upper side of leaf
lower side of leaf
Upper epidermis – transparent, no chloroplasts
nucleus
Palisade cell – many chloroplasts
vacuole
cytoplasm
Chloroplast – membranes covered with chlorophyll
Spongy mesophyll cells – fewer chloroplasts
xylem – transports water
phloem – transports food (translocation)
Air space
lower epidermis
Stoma
Guard cells

5. Outer layer- upper surface
1.waxy 2.
Epidermis transparent so no chlorophyll
1. The waxy cuticle is a waterproof layer which cuts down water loss by evaporation.
2. The upper cells of the leaf make up the epidermis.
They are transparent so light passes straight through them into the next layer of cells…

6. Outer layer- bottom surface
Leaf epidermis with stomata- scanning electron microscope
State that plants take in carbon dioxide from the air through stomata which can open and close
Interpretation- stomata are tiny pores on the surface of a leaf.
Carbon dioxide enters the leaf through stomata.
During the day stomata are open.
During the night stomata are closed.
Know that water vapour is lost through stomata
On the lower surface of the leaf there are tiny pores called stomata (singular- stoma) which open and close.
Stomata let CO2 diffuse in.
Water vapour and oxygen (O2) move out.

7. Guard Cells
Stoma

8. Function of Stomata
What process involves using CO2 and H2O releasing O2 as a waste product?
Photosynthesis
If the plant needs water for photosynthesis, why is water coming out of the stoma?
Guard Cells
Guard Cells
What goes out? O2
H2O
CO2
What goes in?
Stoma Open
Stoma Closed
Stoma

9. Function of Guard Cells
These stomata (leaf openings) naturally allow water to evaporate out.
Why would the plant close stomata with guard cells?
Prevent excess water loss (conserve water)
So what is the point of having stomata?
Allow gas exchange for photosynthesis
Guard Cells
Guard Cells
Stoma Open
Stoma Closed
Guard cells open by inflating with extra water. They do this by pumping K+ ions into the cell, which causes water to rush in via osmosis to diffuse the high ion concentration.

10. Stomata- open
Stomata have guard cells surrounding them to control their opening & closing.
When there is plenty of water (daytime) the water enters the guard cells and becomes turgid and curved.
This opens the stomata and water can escape.

11. Stomata- closed
When there is little water the guard cells loose water and become flaccid = less curved.
This closes the stomata and keeps water in the leaf. This happens at night. G