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The Chapter in Review
Summary
18.1
Onto Land
The Ancestry of Plants

Plants (kingdom Plantae) probably evolved from a multicellular, freshwater green alga about 500 MYA. The freshwater green algae known as charophytes appear to be the closest living relatives of land plants. Whereas algae are adapted to life in the water, plants are adapted to living on land. The charophytes have some characteristics that could be helpful on land. During the evolution of plants, five significant events are associated with adaptation to a land existence: Evolution of the (1) embryo protection, (2) vascular tissue, (3) megaphylls, (4) seeds, and (5) the flower.

Alternation of Generations

Land plants have an alternation of generations life cycle, in which each type of plant exists in two forms, the sporophyte (2n) and the gametophyte (n):

18.2
Diversity of Land Plants
Nonvascular Plants

Bryophytes, represented by the mosses, are plants with the following characteristics:

  • There is no well-developed vascular tissue.

  • The gametophyte is dominant, and flagellated sperm swim in external moisture to the egg.

  • The sporophyte is dependent on the gametophyte.

  • Windblown spores disperse the gametophyte.

Vascular Plants

In vascular plants, the dominant sporophyte has two kinds of well-defined conducting tissues. Xylem is specialized to conduct water and dissolved minerals, and phloem is specialized to conduct organic nutrients and hormones. Certain vascular plants are seedless (lycophytes and ferns). They were large and abundant during the Carboniferous period.

Lycophytes have true roots, stems, and leaves because they contain vascular tissue. Vascular tissue allows lycophytes and other vascular plants to attain greater size due to more efficient transport of water, minerals, nutrients, and hormones. Lycophytes have narrow leaves called microphylls.

Ferns have large leaves with branching veins called megaphylls. Megaphylls enhance food production by photosynthesis. Ferns also have the following life cycle which is typical of seedless vascular plants:

  • The sporophyte generation is dominant and produces windblown spores.

  • The gametophyte is separate and independent. Flagellated sperm swim in external moisture to the egg.

Seed Plants have reproductive structures that are protected from drying out. Seed plants have male and female gametophytes. Gametophytes are reduced in size. The female gametophyte is retained within an ovule, and the male gametophyte is the mature pollen grain. The fertilized ovule becomes the seed, which contains a sporophyte embryo, food, and a seed coat.

  • Gymnosperms are cone-bearing plants, represented by the pine tree. They have “naked seeds” because the seeds are not enclosed by fruit, as are those of flowering plants.

  • Angiosperms are the flowering plants. Angiosperm reproductive organs are in the flower. Pollen is produced in pollen sacs inside an anther. Pollen is transported by wind, or from flower to flower by birds, insects, or bats. Fertilized ovules in the ovary become seeds, and the ovary becomes the fruit. Thus, angiosperms have “covered seeds.”

18.3
The Fungi

Kingdom Fungi includes unicellular yeasts, multicellular mushrooms and molds, and flagellated chytrids.

General Biology of a Fungus

Fungi are neither animals nor plants.

  • The body of a typical fungus is composed of thin filaments of cells, called hyphae, that form a mass called a mycelium.

  • The cell wall contains chitin.

  • Most fungi produce windblown spores during both asexual and sexual reproduction.

Ecological Benefits of Fungi
  • Fungi are saprotrophs that carry on external digestion. As decomposers, fungi keep ecological cycles going in the biosphere.

  • Lichens (fungi plus cyanobacteria or green algae) are primary colonizers in poor soils or on rocks.

  • Mycorrhizal fungi grow on or in plant roots and help the plant absorb minerals and water.

Economic Benefits of Fungi
  • Fungi help produce foods and medicines, as well as serving as a source of food themselves.

Fungi as Disease-Causing Organisms
  • Fungal pathogens of plants include blasts, smuts, and rusts that attack crops of great economic importance, such as rice and wheat.

  • Animal diseases caused by fungi include thrush, ringworm, chytridiomycosis, and histoplasmosis.

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Key Terms
Testing Yourself

Choose the best answer for each question.

  1. Which of the following is not a plant adaptation to land?

    1. recirculation of water

    2. protection of embryo in maternal tissue

    3. development of flowers

    4. presence of vascular tissue

    5. seed production

  2. Plant spores are

    1. haploid (n).

    2. produced by gametophytes.

    3. produced by sporophytes.

    4. diploid (2n).

    5. Both a and c are correct.

  3. Charophytes

    1. are freshwater green algae.

    2. lack vascular tissue.

    3. are the closest living relatives of land plants.

    4. enclose their zygotes within protective structures.

    5. All of these are correct.

  4. Which of the following is a true statement?

    1. People don't eat mushrooms because they might be poisonous.

    2. Penicillin is derived from a fungus.

    3. The alcohol from yeast fermentation makes bread rise.

    4. Fungi are prokaryotes like bacteria.

    5. Fungi ingest their food in the same way animals do.

  5. Label the parts of the generalized plant life cycle in the following illustration.

    For questions 6–13, identify the group(s) to which each feature belongs. Each answer in the key may be used more than once. Each question may have more than one answer.

    Key:

    1. mosses

    2. lycophytes

    3. ferns

    4. gymnosperms

    5. angiosperms

  6. have megaphylls

  7. exhibit alternation of generations

  8. produce seeds

  9. lack true roots, stems, and leaves

  10. produce ovules that are not completely surrounded by sporophyte tissue

  11. produce swimming sperm

  12. produce flowers

  13. protect the embryo as well as the zygote

  14. Label the parts of the flower in the following illustration.

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  16. Lichens

    1. can live on bare rocks.

    2. can only survive in nutrient-rich soils.

    3. are parasitic on trees.

    4. can reproduce asexually.

    5. Both a and d are correct.

  17. A fruit is derived from

    1. the corolla.

    2. an ovary.

    3. an ovule.

    4. the calyx.

  18. Which of the following statements about fungi is false?

    1. Most fungi are multicellular.

    2. Fungal cell walls are composed of cellulose.

    3. Most fungi are nonmotile.

    4. Fungi digest their food before ingesting it.

  19. Chytrids are

    1. a group of fungi with flagellated spores and gametes.

    2. responsible for a serious infection in frogs.

    3. a group of flowering plants that produce “naked seeds.”

    4. the immature leaves of ferns.

    5. Both a and b are correct.

  20. A fungal spore

    1. contains an embryonic organism.

    2. germinates directly into an organism.

    3. is often windblown.

    4. is most often diploid.

    5. Both b and c are correct.

  21. Mycorrhizal fungi

    1. are a type of lichen.

    2. help plants gather solar energy.

    3. help plants gather inorganic nutrients.

    4. All of these are correct.

  22. Which is the largest group of land plants?

    1. angiosperms

    2. lycophytes

    3. bryophytes

    4. gymnosperms

    5. ferns

  23. The gametophyte is the dominant generation in

    1. ferns.

    2. mosses.

    3. gymnosperms.

    4. angiosperms.

    5. More than one of these are correct.

  24. A seed is a mature

    1. embryo.

    2. ovule.

    3. ovary.

    4. pollen grain.

  25. A mushroom is like a plant because it

    1. is a multicellular eukaryote.

    2. produces spores.

    3. is adapted to a land environment.

    4. is photosynthetic.

    5. All but d are correct.

  26. Xylem is

    1. a polysaccharide found in the cell walls of all fungi.

    2. a plant vascular tissue that transports water and minerals.

    3. a plant vascular tissue that transports organic compounds.

    4. a polysaccharide found in the cell walls of all plants.

    5. the part of a flower that produces pollen.

  27. The male gametophyte in seed plants is the

    1. pollen grain.

    2. endosperm.

    3. cone.

    4. megaspore mother cell.

    5. seed.

  28. Which of the following is a saprotroph?

    1. photosynthetic organism

    2. pine tree

    3. nonvascular plant

    4. decomposer

    5. fern leaf

  29. A mycelium is

    1. a mass of fungal filaments.

    2. a type of fungus with flagellated spores and gametes.

    3. the main body of a typical fungus.

    4. a mutualistic association between a fungus and a green alga or cyanobacterium.

    5. Both a and c are correct.

  30. Which of these were among the first land plants with well-developed vascular tissue?

    1. angiosperms

    2. ferns

    3. lycophytes

    4. gymnosperms

    5. bryophytes

Thinking Scientifically
  1. Bare-root pine tree seedlings transplanted into open fields often grow very slowly. However, pine seedlings grow much more vigorously if they are dug from their native environment and then transplanted into a field, as long as some of the original soil is retained on the seedlings. Why is it so important to retain some native soil on the seedlings?

  2. Evolutionary trees like the one here indicate that members of kingdoms Plantae and Fungi both had protist ancestors. All three groups of organisms belong to which domain? What characteristics would distinguish the protist ancestors of plants from those of fungi?

Bioethical Issue
Scientific Limitations

Bristlecone pines are among the oldest trees on Earth. In 1964, a graduate student working in the southwestern United States took core samples from several trees to determine their age. One tree was found to be over 4,000 years old. When the student's coring tool broke, the U.S. Forest Service gave him permission to cut down the tree in order to accurately determine its age. The tree was found to be 4,862 years old—the oldest known living creature on Earth.

Did the student do anything wrong, scientifically or morally, considering that he was given permission to cut down the tree? Who should be responsible for protecting unique trees like the bristlecone pine?

Essentials of Biology Website

The companion website for Essentials of Biology provides a wealth of information organized and integrated by chapter. You will find practice tests, animations, videos, and much more that will complement your learning and understanding of general biology.

http://www.mhhe.com/maderessentials2