Chapter 22 The Land Plants - Warner Pacific Universityclasspages.Warnerpacific.edu/SRamos/BIO102...

© Cengage Learning 2016

Chapter 22

The Land Plants


22.2 Plant Ancestry and Diversity

• Plants

– Multicelled

– Photosynthetic eukaryotes

– Adapted to life on land

– Close relatives of red algae and green algae

– Contain cellulose cell walls and chloroplasts

• Chlorophylls a and b

– Embryophytes

• Embryos form within chamber of parental tissues

• Receive nourishment during development


Plant Ancestry and Diversity

• Adaptive radiation

• First plants evolved 500 million

years ago

– Photosynthetic cells had released

oxygen into the atmosphere and

ozone layer had formed

• Plant spore


Plant Ancestry and Diversity

• Plant spore

– Haploid cell with a cell wall

• Some plants have alternating generations

– A life cycle in which a diploid generation alternates with a haploid

one

– Diploid

– Haploid


Meiosis

Haploid (n)

Phase of Cycle sporesgametes

multicelled

gametophyte

zygote Diploid (2n)

Phase of Cycle

Fertilization

Stepped Art

multicelled

sporophytemitosis


Major groups of plants

• Criteria

– Vascular

– Seed production

– Types of seeds produced

– Development and morphology


Evolutionary Trends Among Plants

• Story of plant evolution

– Adapted to life on land

– Adapted to increasingly drier habitats

• Sporophyte dominates all vascular plant

life cycles

– Spores more likely to survive in dry

conditions

• Oak tree

– Large and complex sporophyte

– Gametophyte: only a few cells



• Genetic factors

– Influenced sporophyte dominance

• Structural adaptations

– Cuticle

• Helps reduce evaporative water loss

– Stomata

• Open to allow gas exchange for

photosynthesis

• Close to conserve water



• Vascular tissues

– Internal system of pipelines

– Xylem distributes water

– Phloem distributes sugars

– Lignin provides structural support

• Leaves

– Contain veins of vascular tissue

– Allow plant to capture sunlight

and exchange gases


Pollen and Seeds

• Pollen grains

– Walled, immature gametophyte

• Gives rise to male gametes

– Released by seed-bearing vascular

plants

– Travel to female gametophytes on the

wind or in insect bodies

– Allow plants to reproduce even in dry

environments


Pollen and Seeds

• Seeds

– Consist of an embryo

sporophyte and nutritive tissue

enclosed within a waterproof

seed coat

– Many have features that

facilitate their dispersal

• Angiosperms disperse seeds

inside a fruit


Bryophytes

• Mosses

– Most diverse and familiar group of bryophytes

– Example: Sphagnum (peat moss)

• 350 species

• One of the most economically important bryophytes

• Grow in peat bogs in high latitude regions of Europe,

Asia, and North America

• Blocks are cut, dried, and burned as fuel in Ireland

• Helps soil retain moisture


zygote2

sporophyte (2 n)

spor e (n) released

from sporangium

sperm released from

male gametangium

1gametophyte (n)

male

gametophyte

sperm

egg in female

gametangium

4

female

gametophyte

Fertilization Meiosis

Diploid (2n)

phase

Haploid ( n) phase 3

5

6

7

© 2016 Cengage LearningJane Burton/ Bruce Coleman Ltd.

① The leafy green part of a moss is the haploid gametophyte.

② The diploid sporophyte has a stalk and a capsule (sporangium). It is not photosynthetic.

③ Haploid spores form by meiosis in the capsule, are released, and drift with the winds.

④ Spores germinate and develop into male or female gametophytes with gametangia that produce eggs or sperm by mitosis.

⑤ Sperm swim to eggs.⑥ Fertilization produces a zygote.⑦ The zygote grows and develops into a

new sporophyte while remaining attached to and nourished by the female gametophyte.


Bryophytes

• Liverworts

– Among oldest known fossils of land plants

– Some gametophytes look leafy and others are

flat sheets

– Example: Marchantia

• Hornworts

– Has a pointy, hornlike sporophyte

– Spores form in upright capsule called

sporangium

– Contain chloroplasts


Seedless Vascular Plants

• Oldest vascular plant lineages

• Have flagellated sperm that swim to eggs

• Disperse by releasing spores directly to the

environment

• Two lineages survive today

– Lycophytes

– Monilophytes


Seedless Vascular Plants

• Club mosses

– Often grow on floor of temperate forests

• Whisk ferns and horsetails

– Native to the Southeastern United States

– Includes rushes

• Ferns

– Most diverse and familiar seedless

vascular plant

– Most live in the tropics


1 The familiar leafy form is the diploid sporophyte.

2 Meiosis in cells on the underside of fronds (leaves)

produces haploid spores.

3 After spores are released,

they germinate and grow into

tiny gametophytes that

produce eggs and sperm.

4 Sperm swim to eggs and

fertilize them, forming a

zygote.

5 The sporophyte begins its

development attached to the

gametophyte, but it continues

to grow and live independently

after the gametophyte dies.

3

sperm

egg

rhizome

zygote

mature

gametophyte

(underside)

spore

sori (clusters of sporangia) on underside of frond

Diploid (2n ) phase

Haploid (n ) phase

2

MeiosisFertilization

1mature sporophyte

5young sporophyte

female

gametangium

male

gametangium

4

photo, A. & E. Bomford/ Ardea, London; art, © 2016 Cengage Learning


Rise of the Seed Plants

• Advantages of seed-bearing plants

– Reproductive traits

– Structural traits


seed (embryo

sporophyte in ovule)

zygote (2n) in ovule

fertilization

develop into

Figure 22.21 p365

pollen sac (2n)

sperm-producing male

gametophytes (pollen grains)

microspores (n) in pollen sac

develop into

meiosis

release and pollination

delivers sperm to

Stepped Art

develop into

egg-bearing female

gametophytes in ovule

megaspores (n) in ovule

ovule (2n)

meiosis


Gymnosperms

• Vascular seed plants

– Produce seeds on the surface of ovules

– Some seeds enclosed in a fleshy or papery

covering

• Types

– Conifers

– Cycads

– Ginkgos

– Gnetophytes


Gymnosperms

• Conifers

– 600 species

– Trees and shrubs with woody cones

– Needle-like or scale-like leaves with a thick cuticle

– More resistant to drought and cold than flowering plants

– Evergreen

– Include the longest lived plants

• Some bristlecone pines are 4,000 years old


pollen tube

sperm (n)

1 Scales of pollen

cones hold pollen sacs.

2 Meiosis of cells in

pollen sacs yields microspores ( n).

8 Fertilization

produces a zygote

that develops into

a seed.

9 The seed

germinates and grows into a new sporophyte.

3 Microspores

develop into pollen grains (male game-tophytes) that are released and travel on the wind.

6 Megaspores

develop into egg-

bearing female

gametophyte s

inside the ovule.

7 A pollen grain alights on a scale of an ovulate cone. It germinates

and a pollen tube grows toward the ovule. Sperm form as the tube grows.

© 2016 Cengage Learning; photos, Robert & Linda Mitchell Photography; Robert Potts, California Academy of Sciences; R. J. Erwin/Science Source

5 Meiosis of cells

in ovules yields megaspores ( n).

4 Scales of

ovulate cones contain ovules .

eggs (n)

female

gametophyte

Inside

ovule

zygote (2 n)

seed coat

embryo seed

stored food

sporophyte (2n)

pollen cone with

many scales

One scale sectioned

through pollen sac

One scale sectioned

through ovule

Fer tilization

MeiosisMeiosis

ovulate cone with

many scales


Gymnosperms

• Cycads

– Native to dry tropics and subtropics

• Ginkgos

– One species remains today: Ginkgo biloba

• Native to China

– Deciduous

• Gnetophytes

– Tropical trees

– Desert shrubs

– Leathery vines


Angiosperms – The Flowering Plants

• Vascular seed plants that make

flowers and fruits

• Flower

– Specialized reproductive shoot

– Contain sepals, petals, and stamen

– Innermost part of the flower is the ovary

– After fertilization, ovule matures into seed

• Ovary becomes the fruit


4 An ovule forms on theovary wall. It contains a diploid cell that will undergo meiosis.

5 Meiosis

yields four

megaspores.

Three will

degenerate.

6 The remaining

megaspore devel-

ops into a female

gametophyte tha t

consists of an egg

and six other cells,

including a cell wit h

two nuclei.8 During double fertilization, one

sperm fertilizes the egg to form a zygote; the other fertilizes the cell with

two nuclei to form a triploid (3n) cell.

9 The ovule

develops into a seed.

7 Pollinatio noccurs, and the pollen grain germinates.A pollen tube grows to and through ovary tissue to the ovule, where it releases two sperm.

2 Meiosis

produces microspores.

3 Microspores

develop into pollen grains (male

gametophytes).

ovule

Double Fertilization

1 An anther has

two pollen sacs

with diploid cells

that give rise to

microspores.

pollen sac

of anther

(cutaway

view)

seed coat (2n)

embryo (2 n)

endosperm (3 n)

2n

pollen grain(n)

microspores (n)

megaspores (n)

mature female

gametophyte

in ovule

pollination

pollen

tube

sperm

mature male

gametophyte

seedMeiosis Meiosis

pollen tube

delivers

2 sperm to

ovule

egg

cell with

2 nuclei

© 2016 Cengage Learning


Angiosperms – The Flowering Plants

• 90 percent of all species today are angiosperms

• Angiosperm characteristics that give them a selective

advantage over gymnosperms

– Shorter life cycle

– Animal-pollinated flowers

– Enhanced seed dispersal


Angiosperm Diversity and Importance

Chapter 22 The Land Plants - Warner Pacific Universityclasspages.Warnerpacific.edu/SRamos/BIO102...

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