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