Leaves
Metabolic Factories
Leaf Structure
• Typical leaf has a flat
blade and petiole
which attaches it to the
stem.
• Most are thin
• High surface to
volume ratio
• Capture sunlight and
promote gas exchange
Simple or Compound
• Simple leaves are not
divided; one leaf
attaches to stem
• Compound leaves are
divided into leaflets.
Fine Structure
• Epidermis:
covers surfaces
• Palisade
Mesophyll:
loaded with
chloroplasts
• Spongy
mesophyll:
contain air
spaces
More about Structure
• Veins are
vascular
bundles of
xylem and
phloem
Stomata
• One Stoma, many
stomata
• A tiny opening in the
epidermis that allow
oxygen and water
vapor to escape, and
carbon dioxide to
enter
• More stomata on
underside
Guard cells open
(plumped) and close
(collapsed) stomata
Transpiration
• Water lost through the stomata in
leaves, and to a lesser degree
from evaporation from stems and
other plant parts.
• So how does a plant keep water
supplied to all parts-especially
the highest branches?
• Cohesion-tension theory.
Cohesion-Tension Theory
• Air’s drying power causes transpiration.
• Creates negative pressure (tension)
• Cohesion creates a continuous water
column
• Concentration gradient; water potential
Monocot /Dicot
• Monocot leaves have
parallel veins
• Dicot leaves have
netlike veins