21.4 Leaves TEKS 4B, 5B, 10B, 10C
The student is expected to:
4B investigate and explain cellular processes,
including homeostasis, energy conversions,
transport of molecules, and
synthesis of new molecules;
5B examine specialized cells, including roots,
stems, and leaves of plants...;
10B describe the interactions that occur
among systems that perform the functions
of transport, reproduction, and response in
plants;
10C analyze the levels of organization in
biological systems and relate the levels to
each other and to the whole system
21.4 Leaves TEKS 4B, 5B, 10B, 10C
KEY CONCEPT
Leaves absorb light and carry out photosynthesis.
21.4 Leaves TEKS 4B, 5B, 10B, 10C
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 TEKS 4B, 5B, 10B, 10C
• Mesophyll is between the leaf’s dermal tissue layers.
cuticle
upper
epidermis palisade
mesophyll
spongy
mesophyll
lower
epidermis
21.4 Leaves TEKS 4B, 5B, 10B, 10C
– 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
• Guard cells surround each stoma.
21.4 Leaves TEKS 4B, 5B, 10B, 10C
• Leaves may be simple, compound, or double compound.
Simple leaf Compound leaf Double compound leaf
21.4 Leaves TEKS 4B, 5B, 10B, 10C
• Leaf veins may be parallel or pinnate.
Pinnate veins Parallel veins
21.4 Leaves TEKS 4B, 5B, 10B, 10C
• Leaf margins may be toothed, entire, or lobed.
Toothed margin Entire margin Lobed margin
21.4 Leaves TEKS 4B, 5B, 10B, 10C
Most leaves are specialized systems for photosynthesis.
• There are two types of mesophyll cells.
– both types contain chloroplasts
– palisade mesophyll absorbs sunlight
– spongy mesophyll connects to stomata
xylem
phloem
cuticle
upper
epidermis palisade
mesophyll
spongy
mesophyll
stomata
lower
epidermis
21.4 Leaves TEKS 4B, 5B, 10B, 10C
– for extreme temperatures,
ex: pine needles
• Leaves have many adaptations.
21.4 Leaves TEKS 4B, 5B, 10B, 10C
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
21.4 Leaves TEKS 4B, 5B, 10B, 10C
– for aquatic environments,
ex: water lily
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
21.4 Leaves TEKS 4B, 5B, 10B, 10C
– for aquatic environments,
ex: water lily
– for getting food,
ex: Venus’ flytrap
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines