Plant Evolution Ch21

Students should be able to:

• List the four major plant divisions

• Define the plant life cycle of alternation of generations

• Name which stage is dominant for each plant division (gametophyte or sporophyte)

• List the key terrestrial adaptations for each plant division.

• Name the parts of a flower

Figure 14.25

What is a plant? • Multicellular, photosynthetic eukaryote that

typically lives on land

• Has cell walls made of cellulose

Plants evolved from green algae • The algal ancestors of plants carpeted moist

fringes of lakes or coastal salt marshes

• First moved to land over 500 million years ago

• Charophytes: Closest relatives to land plants

© 2013 Pearson Education, Inc.

Plants vs. Algae

(Adaptations to

their environments)

Leaf performs photosynthesis

Cuticle reduces water loss; stomata regulate

gas exchange

Shoot supports plant

Surrounding water supports

the alga

Whole alga performs photo-

synthesis; absorbs water,

CO2, and minerals from the

water

Alga

Plant

Figure 21-2 p346

Plant life cycle: Alternation of

Generations

Figure 21-3 p347

Plant diversity reflects evolutionary

history (adaptations to life on land)

© Cengage Learning 2015

1 – Bryophytes

(Non-vascular plants)

• No vascular tissue, lack support, flagellated

sperm require water

• Least adapted to life on land

Figure 21-4a p348

In bryophytes, the gametophyte is

dominant

Gametophyte

(Dominant, carpet-like

form)

Sporophyte

(Reduced and not

independent)

Figure 16.8

© Cengage Learning 2015

Peat moss (Sphagnum)

Cutting blocks of

peat in Ireland for

use as fuel. Peat is

the compressed,

carbon-rich

remains of

Sphagnum moss.

© Cengage Learning 2015

2 – Seedless Vascular Plant

• Vascular tissue with lignin enables plants to

grow tall and upright on land

• Still dependent upon water for reproduction

Fern (Pterophyte)

Figure 21-8 p350

In ferns (and all other groups besides

bryophytes), the sporophyte is dominant

© Cengage Learning 2015

Seed Plants

• 90% of living species

• Adaptations for success:

– Seed is survival packet for embryo

– Pollen (no water required!)

© Cengage Learning 2015

How a seed forms

© Cengage Learning 2015

3 -- Gymnosperms

• “Naked seed” – seeds do not develop in

specialized chamber (no fruit)

Cycads

Conifers

Figure 21-12 p354

A pine tree is a sporophyte with the

gametophyte in its cones

© Cengage Learning 2015

4 – Angiosperms

(Flowering Plants)

• Complex reproductive structures (flowers

and fruit)

Apple blossoms and

fruit

Figure 21-14 p356

Structure of a typical flower

© Cengage Learning 2015 Figure 21-15 p356

An angiosperm plant is a sporophyte

with gametophytes in its flowers

Fruits: Adaptations that help disperse seeds

Wind-dispersed seeds

Fruits: Adaptations that help disperse seeds

Hitchhikers: seeds carried by

animals

Fruits: Adaptations that help disperse seeds

Seeds within edible fruits

Key Haploid (n)

Gametophyte

(n) Sporophyte

(2n)

Sporophyte (2n)

Gametophyte

(n)

Gametophyte

(n)

Sporophyte

(2n)

Diploid (2n)

Seed plants have a greater development of the diploid

sporophyte compared to the haploid gametophyte

generation.

Comparison of alternation of generations

Seed plants Ferns Mosses

The Beauty of Pollination – Moving Art

• Moving Art

Figure 16.UN08

Origin of gametangia

(protect gametes

and embryos)

Origin of vascular

tissue (conducts water and nutrients)

Origin of seeds (protect

embryos from dessication and other hazards)

Origin of flowers (bear ovules

within protective chambers called

ovaries)