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

upperepidermis

palisademesophyll

spongymesophyll

lowerepidermis

21.4 Leaves

– 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

• Leaves may be simple, compound, or double compound.

Simple leaf Compound leaf Double compound leaf

21.4 Leaves

• Leaf veins may be parallel or pinnate.

Pinnate veinsParallel veins

21.4 Leaves

• Leaf margins may be toothed, entire, or lobed.

Toothed margin Entire margin Lobed margin

21.4 Leaves

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

upperepidermis

palisademesophyll

spongymesophyll

stomata

lowerepidermis

21.4 Leaves

– for extreme temperatures, ex: pine needles

• Leaves have many adaptations.

21.4 Leaves

• Leaves have many adaptations.

– for extreme temperatures, ex: pine needles

– for water loss,ex: cactus spines

21.4 Leaves

– 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

– 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