1. Structure of leaves

2. External structures of a leaf
Veins
Lamina
Mid rib
Show them a big leaves
Briefy identify major parts of a leaf.
Ask: what are the 2 major components of a vascular bundle.
petiole
Stem

3. External structure of a leaf
Thin and flat lamina:
- Allows rapid diffusion of carbon dioxide into the leaves.
- Capture maximum amount of sunlight.
Branching network of veins:
- Supply water and mineral salts.
- Remove sugar products of photosynthesis.
Leaves held out at an angle by the petiole,
arranged to prevent overlapping:
- Able to achieve maximum exposure to light.
show them 2 different kinds of branches

4. Internal structure of the lamina
1) Upper epidermis
2) Mesophyll
3) Lower epidermis

5. Internal structure of lamina
Upper and lower epidermis
Single layer of cells
Covered with waxy cuticle
Prevent excessive evaporation of water
Transparent to allow sunlight to pass through

6. Internal structure of lamina
Tell the difference between the spongy and the palisade layer
Use white board

7. Compare and Constrast Palisade mesophyll Spongy Mesophyll
Shape of cells
Long, cylindrical
Irregular in shape
Packing
Closely packed
Loosely packed
Air spaces
Absent
Present
Chloroplasts
Numerous
Less
Vascular bundles

8. Mesophyll layer More chloroplasts found in the palisade layer
more light energy can be absorbed nearer to the leaf surface.
Interconnecting air spaces
Rapid diffusion of carbon dioxide into the mesophyll cells.
Vascular bundles contain of xylem and phloem.
Xylem transport water and mineral salts from roots to leaf.
Water move out of veins and move through the cells by osmosis.
Phloem transport sugar away from leaves.

9. Stomata (s: stoma) Minute pores found at the lower epidermis.
Size of the pores controlled by guard cells.
Contains chloroplasts for photosynthesis

10. Opening and closing of stomata
Stomata found on the underside of the leaves
functions:

11. Functions of stomata and guard cells
Stomata allows diffusion of CO2 , O2 and water vapour into and out of the cells.
Guard cells regulates the size of the stomata.
Eg: on a very hot day, guard cells become flaccid, stomata closes to reduce water loss.

12. Opening of stomata Day time Photosynthesis generates chemical energy.
Energy pumps potassium (K+) ions from the epidermal cells into the guard cells.
Water potential in the guard cell decrease.
Water enters by osmosis.
Guard cells swells, becomes turgid and pull the stomata open.

13. Closing of stomata Night time
Potassium ions diffuse out of the guard cells.
Water potential in the guard cells increases.
Water leaves by osmosis.
Guard cells becomes flaccid and stomatal pore closes.

14. night time
day time
Guard cells turgid
Stoma Opens
Guard cells flaccid
Stoma Closes
Stoma

15. How does CO2 enter the leaf?
Lower concentration of CO2
higher concentration of CO2
CO2 diffuses in