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Chapter 29 Plant Diversity I: How Plants Colonized Land. Figure 29.2 Charophyceans: Chara (top), Coleochaete orbicularis (bottom). Figure 3.2 Water transport in plants. Figure 29.14 Three clades that are candidates for designation as the plant kingdom.
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Plant Diversity I:
How Plants Colonized Land
2. Pteridophytes – ferns, horsetails, lycophytes
a. seedless plants
3. Gymnosperms – conifers, ginkgo, cycads, gnetopsids
a. early seed plants
b. produce naked seeds
4. Angiosperms – flowering plants
a. seeds protected by growing in ovaries
b. majority of modern plants are in this group
2. Both have “rosette cellulose-synthesizing complexes” – rose-shaped arrays of proteins that synthesize the cellulose components that make up plant cell walls.
In order to grow on land, the land plants needed to evolve terrestrial adaptations to survive.
a. Embryo develops within female tissue; female plant provides nutrition (sugars, proteins).
b. Placental transfer cells that enhance the transfer of nutrients from the parent to the embryo.
Figure 29.5 (p. 579) – Placental transfer cell in a liverwort (a bryophyte) See Text book.
Two multi-cellular body forms:
a. Gametophyte (haploid) that produces gametes. Gametes fuse to form zygotes that develop into…
b. Sporophytes (diploid) that produce spores. Spores are haploid cells that can develop into a new organism without fusing with another cell.
a. Gametangia are the gametophyte forms of bryophytes, pteridophytes, and gymnosperms. Gametes are produced within these organs.
b. Female gametangia are called archegoniaà (produce and retain egg cells)
c. Male gametangia are called antheridiaà (produce sperm)
a. Epidermis covered by a waxy cuticle to prevent excess loss of water. Pores (stomata) in cell layer can be opened and closed to allow O2 out and CO2 in.
b. Except for bryophytes, land plants have vascular tissue in roots, stems, and leaves.
- Xylem consists of dead cells that carry water and nutrients from roots to the rest of the plant.
- Phloem consists of living cells that distribute sugars and amino acids throughout the plant.
Xylem and phloem in the stem of Polypodium, a fern (a pteridophyte)
A. Theory is that land plants evolved from charophycean algae over 500 million years ago.
1. Homologous chloroplasts
2. Homologous cell walls made of cellulose
3. Homologous peroxisomes
4. Similar DNA sequences
B. Alternation of generations in plants may have originated by delayed meiosis
Zygote à Sporophyte à Many, many spores
1. Occurs on land because it’s more difficult to produce zygotes. (No water for swimming sperm)
2. By producing sporophyte, many gametophytes can be produced from one zygote because many, many spores are produced. This maximizes output of sexual reproduction.
C. Adaptations to shallow water pre-adapted plants for living on land
1. Charophycean algae inhabit shallow waters and need to survive when water levels drop. Lead to increasing ability to survive entirely on dry land.
A. Gametophyte is the dominant generation in the life cycles of bryophytes
1. Bryophyte sporophytes produce and disperse huge numbers of spores.
1. Bryophytes were the world’s only plants for 100 million years.
2. Peat bogs are made mostly of moss called sphagnum. They contain 400 billion tons of carbon and cut down the amount of greenhouse gases. Peat is harvested, dried, and used as a fuel.
3. Sphagnum is harvested for use as a soil conditioner and plant packing material.
Examples of pteridophytes (seedless vascular plants) – next page…………….
1. There is evidence that roots evolved from subterranean portions of stems.
2. There are two types of leaves:
a. Leaves of lycophytes are microphylls. Microphylls are small leaves with a single, unbranched vein.
b. Leaves of other modern vascular plants are megaphylls. Megaphylls are typically larger and have a branched vascular system.
B. Sporophyte-dominant life cycle evolved in seedless vascular plants (Pteridophytes)
1. Alternation of generations
2. Dominant sporophyte versus dominant gametophyte in bryophytes.
3. Plants are dispersed to new environments as spores; no seeds present
1. Dominant plants in Carboniferous period
2. Extensive beds of coal from these plants
Artist’s conception of a Carboniferous forest based on fossil evidence