The document discusses the structure and function of leaves. It describes the external and internal structures of leaves, including the epidermis, stoma, palisade and spongy mesophyll layers, and vascular tissues. Leaves have adaptations for gas exchange, such as their flattened shape, thinness, internal air spaces, and stomata, which allow diffusion of carbon dioxide during photosynthesis. The document also compares monocot and dicot leaf structures.

1. LEAF STRUCTURE &
FUNCTION

2. Role of leaves:
Trap light for photosynthesis
Exchange gases

3. Leaves do not shade each other
To trap as much light as possible

4. External structure of a leaf
margin
petiole
[leaf stalk]
midrib vein
lamina
[blade]

5. Monocot & Dicot leaves
Long & slender leaf
Parallel veins
Broad leaf
Branching veins

6. Veins contain
xylem
&
phloem

7. Xylem & Phloem transport materials
in plants
Xylem transports:
Water + mineral salts
Phloem transports:
Food [sucrose,
amino acids]

8. Internal structure of a leaf
margin
guard cells
Stoma
[plural: stomata]
palisade layer
spongy layer
xylem
phloem

9. Internal structure of a leaf

10. Function of the waxy cuticle:
 prevents loss of water

11. Why are epidermal cells
transparent?
 to allow a lot of light to pas through

12. Vertical section through a leaf
8. Guard cell 7. stoma
1. Waxy cuticle
2. Upper epidermis
3. Palisade
mesophyll cell
4. Air space
5. Spongy mesophyll cell
6. Lower epidermis

13. QUESTION: [MAY, 2010]
Give a biological explanation for the following
statement:
Leaves are well adapted for efficient diffusion
of carbon dioxide. (4)

14. QUESTION: [MAY, 2010]
The flattened shape of leaves increases the surface
area for diffusion. 1 mark
Most plants have thin leaves – this means that the
distance for the carbon dioxide to diffuse from the
outside air to the photosynthesising cells is kept as
short as possible. 2 marks
The many air spaces inside the leaf allow carbon
dioxide to come into contact with lots of cells – this
provides lots of surface area for diffusion. 1 mark
Stomata allow carbon dioxide into the leaf. 1mark

15. Why is the upper leaf surface darker
green than the lower surface?
More chloroplasts in palisade layer than in
spongy layer.

16. Vascular tissue
is present
throughout the
plant

17. What is the function of the:
Stoma: allows exchange of gases
Guard cells: to adjust the opening and
closing of the stoma

18. When are stomata open and when
are they closed?
DAY NIGHT

19. open their stomata
during the NIGHT

20. How do stomata open during the
day?
potassium ions
enter the guard cells
& water follows.

21. Where are stomata located in:

22. Stomata are located:
mostly on the
lower leaf surface
 each leaf surface
has an equal
number of stomata

23. NO stomata in
submerged leaves
 Stomata only on
upper leaf surface
in floating leaves

24. Why are stomata located like this?
Lower leaf surface is
more protected from
the sun
Each leaf surface is
equally exposed to
the sun

25. Stomata are useless:
they are not in
contact with air
Stomata allow gas
exchange with the air

26. Differences between guard cells and
the surrounding epidermal cells.
Guard cells Epidermal cells
1) have chloroplasts Chloroplasts absent
2) are bean-shaped Cuboidal in shape
3) cell walls are not
evenly thick
Cell walls evenly thick

27. Structure of a dicot plant

28. Structure of a dicot plant
Internode
Node
Main/tap root
Veins
Terminal/apical bud
Leaf
Petiole
Lateral/axillary bud
Stem
Lateral roots