Ch. 22 Sec. 2 Bryophytes

I. Groups of Bryophytes Mosses and their relatives are called bryophytes, or nonvascular plants. They do not have vascular tissues, or specialized tissues that conduct water and nutrients.

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.

1. Most common bryophytes Mosses 1. Most common bryophytes Adapted to life in wet habitats and nutrient-poor soils Can tolerate low temperatures Clumps of gametophytes growing together

The Structure of a Moss Capsule Sporophyte Stalk Stemlike structure Gametophyte 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. Leaflike structure 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. Rhizoid

2. Structure a. Shoot i. Looks like a stem with leaves ii. They do not contain vascular tissue b. “Leaves” i. One cell thick ii. Lose water quickly if air is dry c. Rhizoids i. Long cells to anchor them in the ground ii. Absorb water and minerals from soil iii. Water moves into the rest of the plant

3. Reproduction Thin stalks each containing a capsule This is the sporophyte stage

B. Liverworts Gametophytes a. Broad, thin structures b. Draw up moisture from the soil surface Mature gametophytes produce structures that look like tiny green umbrellas a. Carry the structures that produce eggs and sperm

3. Reproduction 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.

C. Hornworts Found only in soil that is damp nearly year-round Gametophytes look like those of liverworts 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.

When a spore lands in a moist place, it When a spore lands in a moist place, it germinates and grows into a mass of tangled green filaments called a protonema As the protonema grows, rhizoids grow into the ground and shoots grow into the air These shoots grow into green moss plants, which are the gametophyte stage of its life cycle

Gametes form in structures at the tips of the gametophytes Sperm are produced in antheridia, the male reproductive structure Eggs are produced in archegonia, the female reproductive structure Some species produce both sperm and eggs on the same plant

Protonema (young gametophyte) (N) Male gametophyte Female gametophyte In bryophytes, the gametophyte is the dominant, recognizable stage of the life cycle and is the form that carries out photosynthesis. Antheridia Archegonia Sperm (N) In bryophytes, the gametophyte is the dominant, recognizable stage of the life cycle and is the form that carries out photosynthesis. Sperm (N) Egg (N)

4. Fertilization produces a diploid zygote a. Grows directly from the gametophyte b. Depends on gametophyte for water and nutrients 5. Mature sporophyte a. Long stalk ending in a capsule b. Haploid spores are produced by meiosis c. Capsule ripens, opens, and spores are scattered

Life Cycle of Bryophytes Mature sporophyte (2N) Capsule (sporangium) Young sporophyte (2N) Gametophyte (N) Zygote (2N) Gametophyte (N) Copyright Pearson Prentice Hall

III. Human Use of Mosses Sphagnum mosses thrive in the acidic water of bogs 1. Dried sphagnum acts as a natural sponge 2. Can accumulate to form peat deposits Peat 1. Csed as fuel 2. Used to improve the soil’s ability to retain water and to increase soil acidity

22–2 Bryophytes Bryophytes have life cycles that depend on water for reproduction. Bryophytes include mosses, liverworts, and hornworts. Bryophytes do not have true leaves, stems, or roots. They grow 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 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 sporophyte matures, it releases the spores which are carried off by wind and water. • When a spore lands in a moist place, it grows into the green, haploid gametophyte plant we think of as moss.