Ch. 22 Sec. 2Ch. 22 Sec. 2

Bryophytes

• Mosses and their relatives are called Mosses and their relatives are called bryophytes, or nonvascular plants. bryophytes, or nonvascular plants. • They do not have vascular tissues, They do not have vascular tissues,

or specialized tissues that conduct or specialized tissues that conduct water and nutrients.water and nutrients.

I. Groups of Bryophytes

• Bryophytes have life cycles that depend on water for reproduction. • Bryophytes draw up water by

osmosis only a few centimeters above the ground.• Bryophytes are low-growing

plants found in moist, shaded areas.

A.A.MossesMosses1. Most common bryophytes 1. Most common bryophytes

a.a. Adapted to life in wet habitats and Adapted to life in wet habitats and nutrient-poor soilsnutrient-poor soils

b.b. Can tolerate low temperaturesCan tolerate low temperaturesc.c. Clumps of gametophytes growing Clumps of gametophytes growing

togethertogether

• The Structure of a Moss

Stalk

Capsule

Sporophyte

GametophyteStemlike structure

Leaflike structure

Rhizoid

Fig. 22-9 Page 557 This illustration shows the structure of a typical moss plant. The green photosynthetic portion is the gametophyte. The brown structure on the tip of the gametophyte is the sporophyte.

2. Structurea. Shoot

i. Looks like a stem with leaves ii. They do not contain vascular tissue

b. “Leaves” i. One cell thickii. Lose water quickly if air is dry

c. Rhizoids i. Long cells to anchor them in the groundii. Absorb water and minerals from soil iii. Water moves into the rest of the plant

a. Thin stalks each containing a capsule

b. This is the sporophyte stage

3. Reproduction

B. LiverwortsB. Liverworts1.1. Gametophytes Gametophytes

a. Broad, thin structures a. Broad, thin structures b. Draw up moisture from the soil b. Draw up moisture from the soil

surface surface2.2. Mature gametophytes produceMature gametophytes produce

structures that look like tiny greenstructures that look like tiny green umbrellas umbrellasa. Carry the structures that producea. Carry the structures that produce eggs eggs and spermand sperm

• Some liverworts can reproduce asexually by means of gemmae.

• Gemmae are small multicellular reproductive structures.

• In some species, gemmae form in gemma cups.

• When washed out of the cup, the gemmae can divide by mitosis to produce a new individual.

3. Reproduction

C. Hornworts1. Found only in soil that is damp

nearly year-round2. Gametophytes look like those of

liverworts3. Sporophyte looks like a tiny green

horn

II. Life Cycle of Bryophytes– Bryophytes reproduce and develop by alternation

of generations.– The gametophyte is the dominant stage of the life

cycle and is the stage that carries out most of the plant's photosynthesis.

The life cycle of a moss illustrates how bryophytes reproduce and

develop

Fig. 22-11 Page 558 In bryophytes, the gametophyte is the dominant, recognizable stage of the life cycle and is the form that carries out photosynthesis. Sporophytes, which produce haploid spores, grow at the top of the gametophyte plant. When the spores are ripe, they are shed from the capsule like pepper from a shaker. In some species, gametes (sperm and eggs) are produced on separate male and female gametophyte plants.

1.1. When a spore lands in a moist place, itWhen a spore lands in a moist place, it germinates and grows into a germinates and grows into a

mass ofmass of tangled green filaments tangled green filaments called acalled a protonema protonema

2.2. As the protonema grows, rhizoids growAs the protonema grows, rhizoids grow into the ground and shoots into the ground and shoots

grow intogrow into the air the air3.3. These shoots grow into green mossThese shoots grow into green moss

plants, which are the plants, which are the gametophytegametophyte stage of its life cycle stage of its life cycle

a.a. Gametes form in structures at the tips of Gametes form in structures at the tips of the gametophytes the gametophytes

b.b. Sperm are produced in antheridia, the Sperm are produced in antheridia, the male reproductive structuremale reproductive structure

c.c. Eggs are produced in archegonia, the Eggs are produced in archegonia, the female reproductive structure female reproductive structure

d.d. Some species produce both sperm and Some species produce both sperm and eggs on the same plant eggs on the same plant

Female gametophyte

Archegonia

Antheridia

Sperm (N)

Sperm (N)

Egg (N)

Male gametophyte

Protonema (young gametophyte) (N)

In bryophytes, the gametophyte is the dominant, recognizable stage of the life cycle and is the form that carries out photosynthesis.

4. Fertilization produces a diploid zygote4. Fertilization produces a diploid zygotea. Grows directly from the gametophytea. Grows directly from the gametophyteb. Depends on gametophyte for water andb. Depends on gametophyte for water and nutrients nutrients

5. Mature sporophyte5. Mature sporophytea. Long stalk ending in a capsulea. Long stalk ending in a capsuleb. Haploid spores are produced by meiosisb. Haploid spores are produced by meiosisc. Capsule ripens, opens, and spores arec. Capsule ripens, opens, and spores are

scattered scattered

Copyright Pearson Prentice Hall

Life Cycle of Bryophytes

Mature sporophyte (2N)

Gametophyte (N)

Gametophyte (N)

Capsule (sporangium)

Young sporophyte (2N)

Zygote (2N)

III. Human Use of MossesIII. Human Use of MossesA.A. Sphagnum Sphagnum mosses thrive in the acidic watermosses thrive in the acidic water

of bogs of bogs 1. Dried sphagnum acts as a natural sponge1. Dried sphagnum acts as a natural sponge2. Can accumulate to form peat deposits2. Can accumulate to form peat deposits

B.B. Peat Peat 1. Csed as fuel1. Csed as fuel2. Used to improve the soil’s ability to2. Used to improve the soil’s ability to

retain water and to increase soil retain water and to increase soil acidity acidity

22–2 BryophytesBryophytes have life cycles that depend on water for

reproduction.Bryophytes include mosses, liverworts, and hornworts.

Bryophytes do not have true leaves, stems, or roots. Theygrow in wet habitats and where soil quality is poor.

Instead of roots, rhizoids anchor mosses to the ground.Bryophyte life cycles have alternation of generations. In

bryophytes, the gametophyte is the dominant stage of the life cycle. Bryophytes have sperm cells that must swim

through water to fertilize eggs. Thus, bryophytes must live in moist habitats.

Bryophytes reproduce both sexually and asexually. They have several structures that produce reproductive

cells. One structure, antheridia makes sperm cells. Another structure, archegonia makes egg cells.

• After fertilization, the diploid zygote grows into a sporophyte.

The sporophyte produces spores. When the sporophytematures, it releases the spores which are carried off by

wind and water.• When a spore lands in a moist place, it grows into thegreen, haploid gametophyte plant we think of as moss.