21.4 Leaves
KEY CONCEPT
Leaves absorb light and carry out photosynthesis.
21.4 Leaves
Most leaves share some similar structures.
• The blade is usually broad and
flat.
– collects sunlight for
photosynthesis
– connects to the stem by a
petiole
blade
petiole
21.4 Leaves
• Mesophyll is between the leaf’s dermal tissue layers.
cuticle
upper
epidermis
palisade
mesophyll
spongy
mesophyll
lower
epidermis
21.4 Leaves
• Guard cells surround each stoma.
– Stomata open and close when guard cells change
shape.
– When stomata are open, water evaporates and gas
exchanges.
– Stomata close at night and when plant loses too much
water.
guard cells
stoma
21.4 Leaves
Most leaves are specialized systems for photosynthesis.
(don’t memorize this, it is just background info)
• There are two types of mesophyll cells.
– both types contain chloroplasts
– palisade mesophyll absorbs sunlight
– spongy mesophyll connects to stomata
cuticle
upper
epidermis
palisade
mesophyll
xylem
spongy
mesophyll
phloem
lower
epidermis
stomata
21.4 Leaves
• Leaves have many adaptations (you’ll get to this later in
the year)
– for extreme temperatures,
ex: pine needles
• .
21.4 Leaves
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
– for aquatic environments,
ex: water lily
21.4 Leaves
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
– for aquatic environments,
ex: water lily
– for getting food,
ex: Venus’ flytrap