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Function of Leaves:
1.
2.
Collect sunlight in order to perform
photosynthesis
Exchange gases without losing too much
water
Leaves have large thin, flattened sections
called blades
o Blade is attached to the stem by a thin
structure called the petiole
Leaves contain specialized tissue
1. Epidermal cells
2. Parenchyma cells
3. Vascular cells
Epidermis along with the cuticle form a waterproof
barrier that controls water loss (but prevents gas exchange)
• Problem: Gases must be dissolved in water in
order to be exchanged
• Plants need to “breathe”
•
•
Take in CO2 and expel O2 during photosynthesis
Take in O2 and expel CO2 when they use the food they make (like
us)
•
Gases must be dissolved in water in order to be
exchanged, the waterproof barrier prevents
water loss; How do they exchange gas? (i.e.
“breathe”)
• Solution: Stomata
o Stomata (singular: stoma)
small openings on the
underside of the leaf
that open and close to
allow gas exchange
Stomata formed by two special cells called guard cells
o Changes in water pressure in the guard cells causes the
stomata to open and close
• High water pressure = open stoma
• Water is lost while gases are exchanged
• Low water pressure = closed stoma
• No water loss but no gas exchange
• Guard cells have a very important
job, they must balance water loss
against the need to exchange
gases!
•
Vascular tissue in the leaves is connected to
vascular tissue in the stem
•
Xylem and Phloem tissue gathered together in bundles that
form the veins in the leaf
•
Leafs are mainly comprised of specialized
parenchyma tissue called mesophyll
•
Mesophyll cells have chloroplasts and do most of the
plant’s photosynthesis
•
Under the epidermis are mesophyll cells that
make up the Pallisade layer
•
Most of the photosynthesis take place in the pallisade
layer
•
Under the pallisade layer is the Spongy mesophyll
•
Looks like a “sponge” due to many air spaces between
each cell
•
Air spaces connect with stoma and allow CO2 and O2 rapidly
move to all cells

What is the function of the epidermis and cuticle layers?
o
o

To prevent the plant from losing too much water
What is the function of the openings in these layers?
• To open in order to allow gas exchange when needed
and then close to prevent water loss
Describe the location and function of mesophyll tissue
o
o
o
Sandwiched between the upper and lower epidermis
Pallisade layer – performs most of the photosynthesis and stores
food
Spongy layer – performs some photosynthesis but loose spongy
nature maximizes gas movement