Chapter 7 : Nutrition in Plants
7.2 Leaf Structure and function
External Structure of Leaf
• Network of Veins
– Veins carry water, mineral salts and manufacture
food.
• Lamina
– Large flat surface so as to obtain maximum light
for photosynthesis. Lamina allow carbon dioxide
to rapidly reach inner cells.
• Petiole
– Holds lamina away from stem. So as to obtain
sufficient sunlight and air.
Internal Structure of Leaf
1. Upper Epidermis
 Waxy Cuticle: Prevent loss of water, transparent to
allow sunlight to pass through
 Single layer of closely packed cells.
Internal Structure of Leaf
2. Palisade Mesophyll
 Closely packed, long and cylindrical cells
 Contains numerous chloroplast : Absorb maximum
sunlight for photosynthesis.
Internal Structure of Leaf
3. Spongy Mesophyll
 Irregularly shaped cells
 Contains numerous large intercellular spaces : for
diffusion of gases
 Fewer chloroplast as compared to palisade mesophyll.
Internal Structure of Leaf
3. Spongy Mesophyll
 Cells are layered with a thin film of moisture : Allow
Carbon Dioxide to dissolve in
 Presence of vascular bundle (xylem + phloem)
Internal Structure of Leaf
4. Lower Epidermis
 Single layer of closely packed cells
 Cuticle
 Many minute opening known as stoma : Important of
gaseous exchange
Guard Cells
• Bean-shaped
• Contains chloroplast.
Difference between Guard Cells
and Epidermis Cells
Shape
Chloroplast
Cell Wall
Function
Guard Cells
Bean-shaped
Epidermis Cell
Irregular shaped
√
Cell wall near the
stoma is thicker than
elsewhere.
X
Uniform cell
thickness
Controls diffusion rate
Does not control
diffusion
Internal Structure of Lamina: Guard
Cells
• During Day,
1. Water potential of guard cell decreases.
2. Water from neighbouring cells would start to
enter guard cells by osmosis
3. Guard cells become turgid.
Internal Structure of Lamina: Guard
Cells
• During Night,
1. Water potential of guard cell increases.
2. Water from neighbouring cells would start to
leave guard cells by osmosis
3. Guard cells become flaccid.
How does Carbon Dioxide and Water
enter the leaf?
• Carbon dioxide enter the leaf through the
stomata.
• Water is transported in the leaf through
xylem (vascular bundle)
How does Carbon Dioxide enter the
leaf?
• Through stomata
• Carbon dioxide is used for photosynthesis
• During the day, carbon dioxide is rapidly
used up during photosynthesis
• As a result, there is a lower concentration
of carbon dioxide in leaf.
• Carbon dioxide from air would then diffuse
into leaf through stomata and goes into
mesophyll cells.
How does Water enter the leaf?
• Vascular bundle – xylem and phloem
• Xylem transports water and dissolved
minerals from roots to leaf
• Water and mineral salts move from xylem to
mesophyll cells.
• Water is used for photosynthesis.