| Chapter 29 Review |
To review the Activities and/or Investigations listed in Chapter 29 below, go to the Campbell BIOLOGY 7th edition Web site and select "Chapter 29" from the dropdown menu.
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| SUMMARY OF KEY CONCEPTS |
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 Concept 29.1
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Land plants evolved from green algae
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 Morphological and Biochemical Evidence |
The traits shared by plants and charophyceans include rosette cellulose–synthesizing complexes, peroxisome enzymes, similarities in flagellated sperm structure, and formation of phragmoplasts during cell division.
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| Genetic Evidence |
Similarities in nuclear and chloroplast genes suggest that charophyceans are the closest living relatives of land plants.
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| Adaptations Enabling the Move to Land |
Traits such as sporopollenin allow charophyceans to withstand occasional drying along the edges of ponds and lakes. These traits may have enabled the algal ancestors of plants to survive in terrestrial conditions, opening the way to the colonization of dry land.
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| Concept 29.2
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Land plants possess a set of derived terrestrial adaptations
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| Defining the Plant Kingdom |
Some biologists think that the plant kingdom should be expanded to include some or all green algae. Until this phylogenetic debate is resolved, this textbook retains the embryophyte definition of kingdom Plantae.
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| Derived Traits of Plants |
| Derived traits that distinguish the clade of land plants from charophyceans, their closest algal relatives, include apical meristems, alternation of generations, walled spores in sporangia, multicellular gametangia, and multicellular, dependent embryos. Additional derived traits, such as the cuticle and secondary compounds, evolved in many plant species. |
Activity Terrestrial Adaptations of Plants
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| The Origin and Diversification of Plants |
| Fossil evidence indicates that plants were on land at least 475 million years ago. Subsequently, plants diverged into several major groups, including bryophytes (nonvascular plants); seedless vascular plants, such as lycophytes and ferns; and the two groups of seed plants: gymnosperms and angiosperms (flowering plants). Most systematists divide plants into ten phyla. |
Activity Highlights of Plant Phylogeny
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| Concept 29.3
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The life cycles of mosses and other bryophytes are dominated by the gametophyte stage
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The three phyla of bryophytes—liverworts, hornworts, and mosses—may not form a clade. Debate continues over the sequence of their evolution
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| Bryophyte Gametophytes |
Liverwort and hornwort gametophytes grow more horizontally, whereas those of mosses are more vertical. Gametophytes are the dominant generation and are typically most visible, such as a mat of moss. Rhizoids anchor gametophytes to the surface. The flagellated sperm produced by antheridia require a film of water to travel to the eggs in archegonia.
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| Bryophyte Sporophytes |
| Sporophytes grow out of archegonia and are dependent on the haploid gametophytes for nourishment. Smaller and simpler than vascular plant sporophytes, they typically consist of a foot, seta (stalk), and sporangium. Hornwort and moss sporophytes have stomata. |
Activity Moss Life Cycle
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| Ecological and Economic Importance of Mosses |
Sphagnum covers great expanses of land as peat bogs and peat lands, playing an important role in the carbon cycle.
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| Concept 29.4
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Ferns and other seedless vascular plants formed the first forests
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| Origins and Traits of Vascular Plants |
Fossils of the forerunners of today’s vascular plants date back about 420 million years ago and show that these tiny plants had independent, branching sporophytes but lacked other derived traits of vascular plants, such as xylem and phloem, roots, and leaves.
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| Life Cycles with Dominant Sporophytes. In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in the example of the familiar leafy fern plant. The gametophytes are tiny plants that grow on or below the surface. |
Activity Fern Life Cycle
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Investigation What Are the Different Stages of a Fern Life Cycle?
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Transport in Xylem and Phloem. Vascular plants have two vascular tissues: xylem and phloem. Xylem conducts most of the water and minerals. Xylem of all vascular plants includes dead cells called tracheids. The lignin in xylem enables most vascular plants to grow taller than bryophytes. Phloem, a living tissue, conducts sugars and other organic nutrients.
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Evolution of Roots. Unlike the rhizoids of bryophytes, roots play an important role in absorbing water and nutrients. Roots may have evolved from subterranean stems. It is unclear whether roots evolved independently in different lineages.
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Evolution of Leaves. In terms of evolution, leaves are categorized into two types: microphylls and megaphylls. Microphylls, leaves with a single vein, evolved first and are typical of lycophytes. Almost all other vascular plants have megaphylls, leaves with a highly branched vascular system. Megaphylls are usually larger, with more photosynthetic productivity.
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Sporophylls and Spore Variations. Sporophylls are modified leaves with sporangia. Most seedless vascular plant species are homosporous, producing one type of spore, which usually develops into a bisexual gametophyte. All seed plants and some seedless vascular plant species are heterosporous, having two types of spores that give rise to male and female gametophytes.
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| Classification of Seedless Vascular Plants |
Seedless vascular plants include the phylum Lycophyta (club mosses, spike mosses, and quillworts) and the phylum Pterophyta (ferns, horsetails, and whisk ferns and relatives). Ancient lycophytes included woody and herbaceous plants that dominated the first forests. Modern lycophytes are small herbaceous plants. Lycophyte sporophytes have upright stems bearing many microphylls and horizontal stems that grow along the surface. Ferns are the most diverse seedless vascular plants. Most fern species are homosporous and produce clusters of sporangia known as sori. Horsetails and whisk ferns are actually close relatives of ferns.
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| The Significance of Seedless Vascular Plants |
Seedless vascular plants dominated the earliest forests. Their growth may have helped produce the major global cooling that characterized the end of the Carboniferous period. The decaying remnants of the first forests eventually became coal.
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| TESTING YOUR KNOWLEDGE |
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Self–Quiz
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1. Which of the following is not evidence that charophyceans are the closest algal relatives of plants? |
| a. similar sperm structure |
| b. similar cell wall structure |
| c. similarities in cell wall formation during cell division |
| d. genetic similarities in chloroplasts |
| e. similarities in proteins that synthesize cellulose |
2. Which of the following characteristics of plants is absent in their closest relatives, the charophycean algae? |
| a. chlorophyll b |
| b. cellulose in cell walls |
| c. alternation of multicellular generations |
| d. sexual reproduction |
| e. formation of a cell plate during cytokinesis |
3. Which of the following is a clade (monophyletic group)? |
| a. bryophytes and seedless vascular plants |
| b. lycophytes and pterophytes |
| c. liverworts, hornworts, and mosses |
| d. seedless vascular plants and seed plants |
| e. charophyceans and bryophytes |
4. Which of the following characteristics do mosses, liverworts, and hornworts share? |
| a. reproductive cells in gametangia; embryos |
| b. branched sporophytes |
| c. vascular tissues, true leaves, and a waxy cuticle |
| d. seeds |
| e. lignified walls |
5. Which of the following is not common to all phyla of vascular plants? |
| a. the development of seeds |
| b. alternation of generations |
| c. dominance of the diploid generation |
| d. xylem and phloem |
| e. the addition of lignin to cell walls |
6. A heterosporous plant species is one that |
| a. produces a gametophyte that bears both antheridia and archegonia. |
| b. produces microspores and megaspores, which give rise to male and female gametophytes. |
| c. produces spores all year long instead of during just one season. |
| d. produces two kinds of spores, one asexually by mitosis and the other sexually by meiosis. |
| e. reproduces only sexually. |
7. Which of the following is diploid? |
| a. the archegonia of a liverwort |
| b. a nonreproductive cell in the gametangia of a moss |
| c. a cell that is part of the stalk (seta) of a moss sporophyte |
| d. a spore produced by a fern sporophyte |
| e. a subterranean gametophyte of a lycophyte |
8. Microphylls are characteristic of which types of plants? |
| a. mosses |
| d. ferns |
| b. liverworts |
| e. hornworts |
| c. lycophytes |
9. During the Carboniferous period, the dominant plants were |
| a. giant lycophytes, horsetails, and ferns. |
| b. conifers. |
| c. angiosperms. |
| d. charophyceans. |
| e. early seed plants. |
10. Which of the following is a land plant that produces flagellated sperm and has a sporophyte–dominant life cycle? |
| a. fern |
| b. moss |
| c. liverwort |
| d. charophycean |
| e. hornwort |
For Self-Quiz answers, see Appendix A.
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Go to the website or CD–ROM for more quiz questions.
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Evolution Connection
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Draw a cladogram that includes a moss, a fern, and a gymnosperm. Use a charophycean alga as the outgroup. (See Chapter 25 to review cladistics.) Label each branch of the cladogram with at least one derived characteristic unique to that clade.
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Scientific Inquiry
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| In April 1986, an accident at a nuclear power plant in Chernobyl, Ukraine, scattered radioactive fallout for hundreds of miles. In assessing the biological effects of the radiation, researchers found mosses to be especially valuable as organisms for monitoring the damage. Radiation damages organisms by causing mutations. Explain why the genetic effects of radiation can be observed sooner in bryophytes than in plants from other groups. Imagine that you are conducting tests shortly after a nuclear accident. Using potted moss plants as your experimental organisms, design an experiment to test the hypothesis that the frequency of mutations decreases with the organism’s distance from the source of radiation. |
Investigation What Are the Different Stages of a Fern Life Cycle?
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Science, Technology, and Society
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Bryophytes (nonvascular plants) and seedless vascular plants are common, and several of them have important economic and ecological uses. Nevertheless, very few are important agriculturally. Why? What attributes do they lack that would make a plant useful in agriculture? What attributes limit their agricultural utility?
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