Leaf Structure and Function
Basic functions
• 1. Photosynthesis: process
which plants use the energy
from sunlight to produce
sugar (for themselves)
• 2. Cellular Respiration: the
process whereby cells use
sugar to release stored
energy
Photosynthesis
• The conversion of
carbon dioxide using
sunlight energy and
water into sugars and
oxygen
• is associated with the
actions of the green
pigment chlorophyll
Leaf Structure
• leaf is a plant organ and is made up of a
collection of tissues
• Like a sandwich!
• 1. The epidermis that covers the upper and
lower parts
• 2. The mesophyll inside the leaf that is rich in
chloroplasts (light absorbers during
photosynthesis)
• 3. The arrangement of veins (the vascular
tissue)
Components of a Leaf
Think about your sandwich you had
for lunch!
1a. Upper Epidermis
• The epidermis is the outer layer of cells covering
the leaf
• forms the boundary separating the plant's inner
cells from the external world
• Has a waxy texture
• Functions: protection against water loss by way
of transpiration, regulation of gas exchange,
secretion of metabolic compounds, and (in some
species) absorption of water
2. Mesophyll
• Most of the inside of the leaf between the
upper and lower layers of epidermis
• Primary location of photosynthesis in the
plant
• Composed of 2 layers
Layers
• A) Palisade Layer: tightly packed cells
that contain choroplasts (convert light
energy in photosynthesis)
• B) Spongy Layer: cells contain many
spaces between them for gas exchange
and carbon dioxide absorption, contain the
plants veins
1b: Lower Epidermis
• Contains pores called stomata
which are surrounded by
chloroplast-containing guard
cells
• stomata regulate the exchange
of gases and water vapor
between the outside air and
the interior of the leaf
• stomata are more numerous in
the lower epidermis of the leaf
than the upper epidermis
Guard Cells
• Guard cells contain chloroplasts, so they
can manufacture food (for the plant) by
photosynthesis
• At night, the sugar is used up and water
leaves the guard cells, so they become
flaccid and the stomata pore closes, this
reduces the amount of water vapour
escaping from the leaf
3. Veins
• Are the vascular tissue of the leaf
• located in the spongy layer of the
mesophyll
• veins are made of: 2 components
• 1. Xylem: tubes that bring water
and minerals from the roots into
the leaf.
• 2. Phloem: tubes that usually
move sap, with dissolved
sucrose, (produced by
photosynthesis) out of the leaf
Where would each term go?
Veins
Mesophyll
Lower
Epidermis
Upper
Epidermis