Introduction to

Plants

Section 22-1

Plants:

dominates the landscape

provide the base for food chains on land

provide shelter, shade and oxygen for

animals

oldest fossiI evidence is about 470

million years old

What is a Plant?

• Members of the kingdom Plantae

• Multicellular eukaryotes with cell walls made of

cellulose

• Carry out photosynthesis using the green

pigments chlorophyll a and b

• Autotrophic, do not gather food, move about or

directly struggle with predators

The Plant Life Cycle

• Alternation of Generations

• Gametophyte (N) or haploid, gamete-

producing plant

• Sporophyte (2N) or diploid, spore-

producing plant

• Gametes = egg & sperm

(haploid cells) when fuse produce

a new diploid individual

• Spores are reproductive cells that

produce a new individual by mitosis

• Plants must be able to reproduce in dry

environments where there is no water

through which gametes move from plants

to plant

What Plants Need To Survive

1. Sunlight

Photosynthesis

Leaves are broad and flat to maximize

light absorption

2. Water and Minerals

All cells require a constant supply of

water

Water is a raw material of

photosynthesis

Plants have developed structures that

limit water loss

Minerals are needed for growth

3. Gas Exchange

Plants take in CO2 to carry out

photosynthesis and give off O2 for

respiration

Gas exchange takes place with the

atmosphere without losing excessive

water

4. Movement of Water and Nutrients

Plants take up water and minerals

through their roots

Food is made in their leaves

Plants have specialized tissues that

carry the water and distribute the food

throughout the plant body

Early Plants

Origins in the Water

• first green plants evolved from multicellular

green algae

• algae have similar reproductive cycles to

plants

• green algae have cell walls and

photosynthetic pigments identical

to those in plants

The First Plants

• The first true plants were still dependent

on water to complete their life cycles

• Early plants were similar to mosses in that

they were simple and grew close to the

ground

• Common in damp swampy regions

• From these first plants others began to

evolve:

– mosses and their relatives

– ferns

– cone-bearing plants

– flowering plants

Overview of the Plant

Kingdom

• Botanists divide the plant kingdom into

four groups based on three important

features:

– water-conducting tissues

– seeds

– flowers

• Today, plant scientists classify

plants by their DNA sequences

Bryophytes Section 22-2

Mosses

Liverworts

Hornworts

• Bryophytes (nonvascular plants) are

mosses and their relatives

• Do not have vascular tissues allowing

plants to conduct water and nutrients.

• Life cycle depends on water for

reproduction.

• Sperm must swim through water to reach

the eggs.

Groups of Bryophytes

• Bryophytes are low-growing plants

found in moist shady areas.

• Found from polar regions to tropical

areas as long as there is water.

• Bryophytes include:

• mosses

• liverworts

• hornworts

Mosses

• Mosses are members of the phylum

Bryophyte

• Grow in areas of moisture (swamps and

bogs, near streams and rain forests)

• Tolerate low temperatures so they can

grow in harsh environments where other

plants cannot.

• It is the most abundant plant in the polar

regions.

• Vary in appearance from miniature

evergreen trees to small, filamentous plants

that resemble a carpet of green

• When mosses

reproduce, they

produce thin stalks,

each containing a

capsule (sporophyte

stage)

• Each moss plant has

a thin upright shoot

that looks like a stem

with tiny leaves

(gametophyte stage)

• These are NOT true stems or leaves

because they DO NOT contain vascular

tissue

• "Leaves" are only one cell thick and lose

water quickly if the air is dry

• DO NOT have "true roots" instead they

have rhizoids which anchor them and

absorb water and nutrients

Liverworts

• Liverworts are members of the phylum

Hepaticophyta

• Some species resemble the shape of a liver

• The gametophyte stage produces gametes

in structures that look like little green

umbrellas

• Reproduce asexually by means of

gemmae which are small circular

spheres that contain many haploid cells

• Gemmae are produced in cuplike

structures called gemma cups

Hornworts

• Hornworts are members of the phylum Anthocerophyta

• Found only in soil that is damp year-round

• Hornworts have sporophytes that looklike tiny green horns

Life Cycle of Bryophytes

• Reproduce with alternation of

generations

• The gametophyte is the dominant,

recognizable stage and the stage that

carries out the most photosynthesis

• The sporophyte is dependent on the

gametophyte for supplying water and

nutrients

Dependence on Water

• For fertilization to occur, the sperm must

swim to an egg

• Sometimes raindrops splash sperm from

one plant to another

• Bryophytes must live in habitats where

water is available

Life Cycle of a Moss

1. A moss spore lands in a moist place, grows into a mass of tangled green filaments called a protonema.

2. The protonema grows and forms rhizoids that grow into the ground and shoots that grow into the air.

3. Shoots grow into the familiar green moss plants which are the gametophyte stage.

4. Gametes are formed in reproductive structures at the tips of the gametophytes.

5. Sperm in the antheridia and eggs cells in archegonia.

Haploid (N)

Diploid (2N) MEIOSIS

FERTILIZATION

Mature sporophyte

(2N)

Gametophyte (N)

Gametophyte (N)

Young sporophyte (2N)

Zygote (2N)

Sperm (N)

Sperm (N)

Egg (N)

Spores (N)

Capsule (sporangium)

Protonema (young gametophyte) (N)

Male gametophyte

Female gametophyte

Antheridia

Archegonia

Life Cycle of a Moss

6. Sperm are released, reach egg cells and

fertilization produces a diploid zygote.

7. The zygote is the beginning of the sporophyte

stage.

8. It grows directly out of the body of the

gametophyte and depends on it for water and

nutrients.

9. The mature sporophyte is a long stalk ending

in a capsule.

10. Inside the capsule, haploid spores are

produced and when the capsule ripens, it opens

releasing the spores to start the cycle again.

Human Use of Mosses

• Sphagnum mosses thrive in acidic water of

bogs. They absorb many times their own weight

and act as a "natural sponge".

• Dead remains of sphagnum accumulate to form

thick deposits of peat and can be cut from the

ground and burned as a fuel.

• Peat moss is also used in gardening.

– Added to soil to improve the soil's ability to retain

water.

– low pH so it increases the soiI's acidity. Plants,

such as azaleas, grow well in acidic soil.

Seedless Vascular Plants

Section 22-3

Evolving about 420 million years ago

were plants that contained vascular

tissue, a type of tissue that is

specialized to conduct water and

nutrients through the body of the plant.

Evolution of Vascular Tissue

• Tracheids are the key cells that

make up the xylem.

–a form of vascular tissue that

carries water up from the roots.

–are hollow cells

with thick cell

walls that resist

pressure.

–connected end

to end like a

series of

drinking straws.

• Phloem is the second type of vascular

tissue.

– it transports nutrients and carbohydrates

produced by photosynthesis

• Vascular plants also produce lignin, a

substance that makes cell walls rigid. It

allows the plant to grow upright and

reach great heights.

Ferns and Their Relatives

• Seedless vascular

plants include:

• Club mosses

• Horsetails

• Ferns (most

numerous)

• Ferns and their

relatives have true

roots, leaves and

stems.

• Roots are underground organs that

absorb water and minerals. Water

conducting tissues are in the center of

the root.

• Leaves are photosynthetic organs and

contain one or more bundles of vascular

tissue.

– This vascular tissue is gathered into veins

made up of xylem and phloem.

• Stems are supporting structures that

connect roots and leaves, carrying water

and nutrients between them.

Club Mosses

• Club mosses belong in the phylum

Lycophyta

• They are small plants that live in

moist woodlands and near

streambeds and marshes.

• Lycopodium,

the common

club moss

looks like a

miniature pine

tree

• Club moss is

also called

"ground pine"

Horsetails

• The only living genus in the phylum

Arthrophyta is Equisetum.

• Its leaves are arranged in whirls at

joints along the stem.

• Equisetum is called

horsetail or

scouring rush

because its stem

look similar to

horses' taiIs and

contain crystals of

silica.

• During Colonial

times, horsetails

were commonly

used to scour pots

and pans.

Ferns

• Ferns are members of the phylum

Pterophyta

• They have true vascular tissue, strong

roots, creeping or underground stems

called rhizomes and large leaves called

fronds.

• Thrive in areas with little light, found in

shadows of forest trees and are

abundant in the Pacific Northwest rain

forests.

Life Cycle of Ferns

• Ferns and other vascular plants have a

life cycle in which the diploid

sporophyte is the dominant stage.

• Fern sporophytes produce haploid

spores on the underside of their fronds

in tiny containers called sporangia.

• Sporangia are grouped into

clusters called sori.

1. When spores germinate, they develop

into haploid gametophytes.

2. The small gametophyte first grows a set

of rootlike rhizoids and then flattens into

a thin, heart shaped, green structure

that is the mature gametophyte.

3. The gametophyte grows independently

of the sporophyte.

4. The antheridia and archegonia are

found on the underside of the

gametophyte.

Haploid gametophyte (N)

Diploid sporophyte (2N)

MEIOSIS

FERTILIZATION

Mature sporophyte (2N)

Gametophyte (N)

Frond

Sperm

Egg

Spores (N)

Antheridium

Archegonium

Developing sporophyte (2N)

Sporophyte embryo (2N)

Mature gametophyte (N)

Young gametophyte (N)

Sporangium (2N)

Life Cycle of a Fern

5. Fertilization requires a thin film of

water for the sperm to swim to the egg.

6. The diploid zygote immediately begins

to grow into a new sporophyte plant.

7. As the sporophyte grows, the

gametophyte withers away.