Plant Structures: Leaves
What is a leaf?
• Leaves are structures produced on stems where
photosynthesis primarily takes place.
Functions:
• Photosynthesis
• Evapotranspiration (loss of water vapor from the stomata)
moves water and nutrients up from the roots.
• Small openings in the leaf (stomata) regulate moisture
and gas exchange and temperature in the plant.
• Used for feed and food.
• Habitat for some organisms
• Used for plant identification
• Used for asexual reproduction (cuttings)
External structure:
Blade = Broad and flat part of the leaf where most of the photosynthesis
of the plant takes place.
Petiole = The thin stalk that connects the leaf to the stem.
Stipule = An outgrowth at the base of the petiole – can be in pairs;
can vary and be in the form of glands, scales, hairs, spines and sometimes
look leaf-like.
Internal structure:
Waxy coating – prevents water
loss – can be thicker in desert
plants
Tightly packed parenchyma
cells filled with chloroplasts
Vascular bundle/ leaf veins - moves
water and nurients through the plant
Parenchyma cells loosely
arranged, help with
movement of O2, CO2 and
water vapor. May contain
chloroplasts
Specialized kidney shaped
cells that open and close the
stomata
Openings that allow for gas
exchange (water vapor, O2, CO2)
Epidermis – Upper – Protect underlying tissues, could have a waxy coating to
prevent water loss.
Lower – Contains stomata
Simple leaf
Blade
Double/Doubly compound leaf
Compound leaf
Leaflets
Leaflet
Simple leaf
Compound leaf
Doubly compound
leaf
Pinnate
venation
Alternate
Whorled
Opposite