Pioneers In a World Without Plants!
B. The invasion of land began with the cyanobacteria, followed by green algae and fungi.
C. Today, there is a rich diversity of green plants, making carbon compounds out of water and carbon dioxide using sunlight as the energy source.
I. Evolutionary Trends Among Plants
2. Most, the gymnosperms and angiosperms, have vascular tissues for transport of water and nutrients; plus they possess root and shoot systems.
3. Nonvascular plants, such as the bryophytes, have simple internal transport systems (no true roots, stems, or leaves).
4. The ancestors of plants had evolved by 700 million years ago, but another 265 million years passed before simple stalked species appeared. Within another 60 million years, plants had radiated through much of the land.
B. Evolution of Roots, Stems, and Leaves
2. Parts above ground developed into shoot systems, adapted for exploiting sunlight and absorbing carbon dioxide from the air.
3. Vascular tissue became increasingly extensive: xylem for conducting water and minerals, phloem for products of photosynthesis.
4. Extensive growth of stems and branches became possible due to the strengthening of cell walls afforded by deposits of lignin.
5. Stems and leaves were covered by cuticle to minimize water loss; evaporation was controlled by opening and closing of stomata (openings).
C. From Haploid to Diploid Dominance
2. The life cycle of complex land plants is dominated by the large, diploid sporophyte.
b. The spore develops into the gametophyte, which produces the gametes.
D. Evolution of Pollen and Seeds
2. In the gymnosperm and angiosperm lineages, the spores are differentiated into two types&endash;heterosporous.
b. The female gametophytes remain in the plant and are surrounded by protective tissues, eventually producing a seed.
3. Over time the sporophytes, while developing extensive root and shoot systems, began holding onto their spores and gametophytes&endash;protecting and nourishing them.
II. Bryophytes
2. Most species do have rhizoids that attach the gametophytes to the soil and absorb water and minerals.
B. These nonvascular plants show three features that were adaptive during the transition to land:
2. A cellular protective jacket surrounds the sperm-producing and egg-producing parts of the plant to prevent drying out.
3. The (dependent) embryo sporophyte begins life inside the (independent) female gametophyte.
C. Mosses are the most common bryophytes.
2. After fertilization, the zygote develops into a mature sporophyte, which consists of a special structure (sporangium) in which the spores develop.
III. Focus on the Environment: Ancient Carbon Treasures
IV. Existing Seedless Vascular Plants
2. It has well-developed vascular tissues.
3. It is the larger, longer lived phase of the life cycle.
B. Although the sporophytes of seedless vascular plants can live on land, their gametophytes cannot because they lack vascular tissues and the male gametes must have water to reach the eggs.
C. Whisk Ferns (Psilophyta)
2. They are popular ornamental plants common to tropical and subtropical areas.
3. The sporophytes have no roots or leaves, but rather consist of a system of scalelike branches.
4. The stem houses the xylem and phloem as well as surface cells capable of photosynthesis.
5. Underneath the ground surface short, branching rhizomes serve an absorptive function.
D. Lycophytes (Lycophyta)
2. The sporophyte has true roots, stems, and small leaves containing the vascular tissue.
3. Strobili bear spores that germinate to form small, free-living gametophytes.
E. Horsetails (Sphenophyta)
2. The sporophytes possess underground stems called rhizomes.
3. The scalelike leaves are arranged in whorls around the hollow, photosynthetic stem.
4. Spores are produced inside cone-shaped clusters of leaves at the shoot tip.
F. Ferns (Pterophyta)
2. Sori are clusters of sporangia that release spores that develop into small heart-shaped gametophytes.
V. The Rise of the Seed-Bearing Plants
2. They also produce megaspores which develop within the ovules which will eventually produce seeds when the sperm fertilizes the egg.
3. Gymnosperms have water-conserving traits, including thick cuticles.
B. The pine tree produces two kinds of spores in two kinds of cones:
2. Female cones produce ovules that yield megaspores (female gametophyte).
3. Pollination is the arrival of a pollen grain on the female reproductive parts, after which a pollen tube grows toward the egg.
4. Fertilization, which is delayed for up to a year, results in a zygote that develops into an embryo within the conifer seed.
VI. Focus on the Environment: Good-bye, Forests
VII. Gymnosperm Diversity
B. Cycads are palmlike trees flourished during the Mesozoic era, but only about 100 species still exist&endash;confined to the tropics and subtropics; they bear massive cone-shaped strobili that produce either pollen (transferred by air currents or insects) or ovules.
C. Ginkgos are represented today by only one hardy, species that has survived from the times of dinosaurs; the tree show remarkable resistance to insects, disease, and air pollutants.
D. Gnetophytes are the most unusual gymnosperms; they live in tropical and desert areas.
VIII. Angiosperms&endash;Flowering, Seed-Bearing Plants
2. This group has dominated the land for 100 million years, living a very diverse habitats.
B. There are two classes of flowering plants:
2. Monocotylendonae (monocots) include grasses, lilies, and the major food-crop grains.
IX. Key Aspects of the Life Cycles
[This section consists solely of a figure depicting the life cycle of the lily.]