Chapter 23 and 24

*Plants

23.1 The Green Algal Ancestor of Plants

• Plants are multicellular, photosynthetic eukaryotes

• Plant evolution is marked by adaptations to a land existence.

• A land environment offers certain advantages Plentiful light for photosynthesis Carbon dioxide is present in higher concentrations

and diffuses more readily in air than in water

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The Green Algal Ancestor of Plants

• Adaptations are required for a land environment Constant threat of desiccation (drying out)

• Protect all phases of reproduction (sperm, egg, embryo) from drying out

• Seed plants disperse their embryos within the seed, which provides the embryo with food within a protective seed coat

• The water environment provides plentiful water support for the body of the plant

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The Green Algal Ancestor of Plants

• To conserve water, the land plant body is covered by a waxy cuticle. Impervious to water while still allowing carbon dioxide to enter so

that photosynthesis can continue• Vascular system transports water in the body of the land

plant.

• Plants are thought to have evolved from freshwater green algae about 450 mya

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Evolutionary History of Plants

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common ancestor

megaphylls

microphylls

seeds

flowers, double fertilization, endosperm, fruit

Flowering plants

Gymnosperms

Ferns and allies

Mosses

Lycophytes

Hornworts

Va

scu

lar

No

nv

asc

ula

r

See

dle

ss

Bry

op

hy

tes

See

d

Liverworts

Charophytes

550 400450500 350 300 250PRESENT

commongreenalgalancestor

embryoprotection

apicalgrowth

vasculartissue

Million Years Ago (MYA)

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The Green Algal Ancestor of Plants

• Additional terrestrial adaptations:

Waxy cuticle to prevent water loss

Stomata to allow gas exchange

Apical tissue, which has the ability to produce complex tissues and organs

Leaf Adaptation

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cuticle

a. Stained photomicrographof a leaf cross section

Stomata

b. Falsely coloured scanningElectron micrograph of leaf surface

400 x

Stomata

Plant leaves have aCuticle and stomata

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(Left): © Kingsley Stern; (Right): © Andrew Syred/SPL /Photo Researchers, Inc.

Evolution of Seed Plants: Full Adaptation to Land

• Flowers and Diversification:

Wind-pollinated flowers are usually not showy

Bird-pollinated and insect-pollinated flowers are often colorful

Night-blooming flowers attract nocturnal mammals or insects

• Usually white or cream-colored and aromatic

Fruits of flowers protect and aid in seed dispersal

• Utilize wind, gravity, water, and animals for dispersal8

• Chapter 24

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24.1 Organs of Flowering Plants• Flowering plants, or angiosperms, are extremely diverse

but share many common structural features. • Most flowering plants possess a root system and a shoot

system The root system simply consists of the roots, The shoot system consists of the stem and leaves.

• A typical plant features three vegetative organs roots, stems, and leaves Vegetative organs are concerned with growth and

nutrition.• Flowers, seeds, and fruits are structures involved in

reproduction.10

Organization of Plant Body

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stem

internode

leaf

petiole

blade

axillary bud

terminal bud

node

vascular tissues

root hairs

primaryroot

branchroot

shoot systemroot system

node

vein

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Organs of Flowering Plants

• Roots Generally, the root system is at least equivalent in

size and extent to the shoot system• Anchors plant in soil

• Absorbs water and minerals from the soil

• Produces hormones

Root hairs:• Projections from epidermal root-hair cells

• Greatly increase absorptive capacity of root

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