Chapter 22 Plant Structure and Function Parts of

Leaves • Leaf is usually flat and wide to maximize light absorption • Is

Stomata • Small openings through which carbon dioxide, water, oxygen, and other gases pass

Cross Section of Leaf • Midrib – extension of the stalk into the leaf

Leaf Structure • Waxy Cuticle – thin layer atop the epidermis – Reduce the

Leaf Structure • Palisade Mesophyll Layer – Where most of photosynthesis occurs – Contain

Leaf Structure • Spongy Mesophyll Layer – Cells are NOT as closely packed –

Leaf Structure • Stoma – Openings in leaf that can open and close –

Leaf Modifications • Cacti – modified leaves called spines • Succulents – water storage

Leaf Modifications • Poison Ivy & Poison Oak – leaves contain toxic substances that

Trichomes • Hairlike projections that protect the plant – Protect from insect and animal

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Chapter 22 Plant Structure and Function

Parts of the Leaf

Leaves • Leaf is usually flat and wide to maximize light absorption • Is where photosynthesis occurs – Site of Sugar and O 2 production – Chloroplasts • Is where transpiration occurs • Have adaptations to prevent drying out

Stomata • Small openings through which carbon dioxide, water, oxygen, and other gases pass • The two cells that border a stoma are guard cells.

Cross Section of Leaf • Midrib – extension of the stalk into the leaf • Vein – branch off from midrib • Lamina – blade of the leaf • Petiole – attaches leaf to the stem

Leaf Structure • Waxy Cuticle – thin layer atop the epidermis – Reduce the water lost from leaf • Epidermis – Form layers on upper and lower surfaces of the leaf – Prevent water from getting out – Keep unwanted substances from getting in – Transparent

Leaf Structure • Palisade Mesophyll Layer – Where most of photosynthesis occurs – Contain a lot of chloroplasts – Closely packed together – Only in upper part of leaf

Leaf Structure • Spongy Mesophyll Layer – Cells are NOT as closely packed – Contains air spaces to enable gases to move in and out – Not as many chloroplasts – Photosynthesis still occurs in this layer

Leaf Structure • Stoma – Openings in leaf that can open and close – Guard cells located on each side of opening – Responsible for transpiration

Characteristics of Leaves

Leaf Modifications • Cacti – modified leaves called spines • Succulents – water storage sites • Pitcher plant – collects water that traps and drowns insects

Leaf Modifications • Poison Ivy & Poison Oak – leaves contain toxic substances that can produce skin irritations. • Squash & Tomato plants – have tiny hairs with trichomes at the tips which repel insects.

Trichomes • Hairlike projections that protect the plant – Protect from insect and animal predators • Some even release a toxic substance – Reflect light to cool plant

Trichomes

The Busy Leaf: Photosynthesis Explained