Download chapter 37: evolutionary history of plants

CHAPTER 30: OVERVIEW OF PLANT DIVERSITY
WHERE DOES IT ALL FIT IN?
Chapter 30 is consistent with strategies of Chapters 27 and 29 and highlights the plant diversity.
Students should be encouraged to recall the principles of eukaryotic cell structure and evolution
associated with the particular features of plant cells. The information in Chapter 30 does not stand
alone. Students should know that plants and other organisms are interrelated and originated from a
common ancestor of all living creatures on Earth.
SYNOPSIS
Today, there are over 300,000 species of terrestrial plants, all most likely evolving from a single
green algal ancestor, which still remains a mystery today. Plants are described as a group of
organisms derived from multicellular algae as evidenced by their chlorophyll b containing
chloroplasts. Characteristics of plants include: photosynthetic, embryo protection, multicellular
haploid and diploid phases, and presence/absence of conducting systems, cuticles, and stomata.
They are divided into two broad categories, vascular and nonvascular plants. Nonvascular plants
comprise three non monophyletic phyla: mosses, liverworts and hornworts. Vascular plants have
complex conducting systems of xylem and phloem that allow for further tissue differentiation of
stems, roots and leaves. They are further divided into non-seed (spore) producers versus seed
producers. Two distinct monophyletic lineages comprise the seedless vascular plants: club
mosses and ferns (including whisk ferns and horsetails). Vascular seed producing plants are
further divided into two major groups (representing seven phyla): gymnosperms with seeds that
protect their embryos (conifers and cycads) and the angiosperms, the dominant land plants today,
with flowers and fruit.
All plants exhibit a haplodiplontic life cycle having multicellular haploid and diploid stages. A
haploid gametophytic generation or “gamete plant” gives rise to haploid gametes that undergo
syngamy to produce a diploid sporophytic generation or “spore plant” which produce haploid
spores. Meiosis takes place in the sporangia, reproductive structure on the diploid sporophyte,
and produce producing four haploid spores that then divide by mitosis that develop into the
multicellular, haploid gametophytes. The more primitive plants exhibit prominent gametophytes
and reduced, dependent sporophytes while the more advanced plants are primarily sporophytic
with reduced, dependent gametophytes. Heterosporous plants produce two different kinds of
spores, homosporous plants produce only one kind of spore.
Three phyla represent approximately 24,700 species of nonvascular plants; the Bryophyta
(mosses), Hepaticophyta (liverworts), and Anthocerotophyta (hornworts). Although diverse and
not truly related, they share four primary characteristics: (1) photosynthetic, independent
gametophytes, (2) a nutritionally dependant sporophyte attached to the gametophyte, (3) they
require water for fertilization, and (4) they are small in size with the gametophyte more
conspicuous than the sporophyte. Mosses possess a central axis of rudimentary water conducting
tissue found in leaflike structures and anchored to the substrate by rhizoids. Reproductive
structures consist of the female gametangia (archegonia) that produce a single egg and male
gametangia (antheridia) which produce numerous sperm. Sperm are released from an
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antheridium and swim using their flagella through rainwater to the archegonia, uniting with a
haploid egg forming a diploid zygote. Zygote divides by mitosis and develops into the
sporophyte, where mother cells undergo meiosis producing four haploid spores. Liverworts and
hornworts lack any form of vascular tissue. All three phyla are well suited for wide ranging
terrestrial habitats, from arid and cold to warm and moist.
Vascular plants possess efficient conducting systems comprised of two elements. Phloem cells
carry carbohydrates away or down from leaves where they are manufactured. Xylem elements
transport water and minerals up from the roots. The less advanced, seedless vascular plants are
similar to mosses; they form antheridia and archegonia, produce free-swimming sperm and
require water for fertilization. They include closely related Pterophyta (ferns, horsetails, whisk
ferns) distantly related Lycophyta (club mosses). In these two phyla there is a greater
development of the sporophyte stage, now photosynthetic and nutritionally independent of the
gametophyte. The ferns with about 365 genera are the most abundant seedless vascular plants
and exhibit diverse morphologies. Most possess horizontal, underground stems called rhizomes
and have leafy fronds that develop from fiddleheads. Nearly all are homosporous with distinctive
sori containing sporangia that contain haploid spores. The horsetails comprise only one genus,
homosporous with motile sperm, either photosynthetic or nonphotosynthetic. Whisk ferns
comprise two genera, are homosporous, have motile sperm, no leaves, and little differentiation
between roots and shoots.
Seed producing, vascular plants are heterosporous, lack antheridia, possess non-flagellated
sperm, and only a few produce archegonia. All seed plants are heterosporous. Their
microgametophytes (male gametes) are called pollen grains and are released directly into the
environment. Their megagametophytes (female gametes) are held within the ovules and are
pollinated when contacted by pollen grains. Pollination and fertilization may be separated by
long periods of time. Five phyla make up the seed producing, vascular plants including the:
angiosperms that produce seeds enclosed within fruits including the phyla of Anthophyta
(flowering plants) and gymnosperms which are plants that produce naked seeds including
phylums: Coniferophyta (pines, spruces, firs, yews, redwoods and other conifers), Cycadophyta
(cycads), Gnetophyta (gnetophytes), and Ginkgophyta (ginkos). All ginko species are in one
genus, have flagellated and motile sperm, deciduous trees. Gnetophyta species are in one of
three genera, have nonmotile sperm, and are the only gymnosperms with vessels. Cycadophyta
phyla include 10 genera, seeds are in cones, sperm are flagellated and motile and include
palmlike plants. Coniferophyta comprises about 50 genera of conifers, have nonmotile sperm,
needlelike or scalelike leaves, and seeds found in cones.
The Angiosperms phyla Anthophyta contain over 250,000 known species of flowering plants and
are divided into two monophyletic classes: the eudicots or “dicots,” which are made up of about
175,000 species and are the more primitive of the two, and the second lineage that gave rise to
the monocots and magnolias with about 65,000 species. Plants in these two lineages, monocots
and dicots, differ according to the number of cotyledons, leaf venation, presence of lateral
meristems, and number of flower parts. Included in the dicots are the majority of fruit and nut
trees, shrubs, snapdragons, mints, and a majority of all vegetables and fruits. Many monocot
plants are mostly annual plants and include the grasses, grains, lilies, cattails, palms, agaves,
yuccas, pondweeds, orchids, and irises. All flowers, modified stems with modified leaves, share
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certain features. The flower originates as a bud at the end of a pedicel (stalk), which expands to
form the receptacle and other flower parts including an outermost whorl of sepals (green and leaf
like), followed by a whorl of colored petals attracting pollinators. The third whorl is comprised
of the androecium or the stamens, made up of the anther and filament. At the center of this whirl
is the gynoecium, the female structures, the carpels. The carpel contains the stigma, style, and the
fruit-developing ovary, containing one to hundreds of ovules. Angiosperms undergo double
fertilization where one sperm cell fuses with the egg to produce the zygote while a second sperm
fuses with two polar nuclei to form the nutritive triploid endosperm. Angiosperm evolutionary
innovations include flowers to attract pollinators, fruits that protect the embryo and aid in its
dispersal, and double fertilization providing for nutritive tissue for the growing embryo.
LEARNING OUTCOMES
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Explain the evidence supporting the evolution of plants from green algae.
Describe haplodiploidy as it relates to the typical plant life and reproductive cycle.
Understand the adaptations necessary for plants to become dominant terrestrial organisms.
Explain why liverworts and mosses are not monophyletic.
Differentiate between vascular and nonvascular plants.
Compare the gametophytic and sporophytic stage of mosses, ferns, gymnosperms, and
angiosperms.
Understand the morphology of gamete production in each of the major plant phyla.
Explain the evolutionary significance of the seed as it pertains to terrestrial life.
Understand how reproduction in a gymnosperm differs in angiosperms.
Differentiate between the two angiosperm lineages.
Describe the structures and function of those structures in a flower.
Describe angiosperm double fertilization.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 30 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students do not fully understand the origins of endosymbionts in plants
Students believe that plants do not carry out cellular respiration
Students believe that plants lack tissues and organs
Students do not equate pollination with sexual reproduction
Students think pollen are one and the same as sperm
Students are unaware that plants produce eggs
Students are unaware that plants undergo embryological development
Student believe that only leaves can carry out photosynthesis
Students believe that the reproductive structure of all plants are flowers
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Students do not know that a change in ploidy is associated with alternation of generations
Students confuse spores with pollen
Students believe that all flowers are insect pollinated
Students believe that the pollen of any plant can be found in the wind
Students believe that grasses are primitive plants while are trees are modern organisms
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
This chapter introduces a lot of new words. Simplify this by breaking the words into their roots
when possible: “phyte” means plant; “micro,” “andro,” and “anth” are associated with male
structures; “mega,” “gyno,” and “arch” are associated with female parts.
Stress the difference between nonvascular and vascular, seedless vascular, and seeded vascular
and how the haplodiplontic life cycle relates to both the gametophyte and the sporophyte.
The multitude of plant life cycles can become very confusing. Present as few as possible to make
your point. It is better to understand the major changes associated with evolution and
specialization. The evolution from a dominant gametophyte to a dominant sporophyte is peculiar
to plants. It is also important to present the advances toward angiospermy as being related to less
dependency on free water for survival and reproduction.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 30.
Application
Analysis
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Have students explain if plants would have evolved without
endosymbionts.
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Have students describe what life cycle of ferns would not be able to
develop if meiosis was inhibited.
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Ask students to identify the equivalent structure to sori in flowering
plants.
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Have students compare and contrast moss and fern life cycles.
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Ask students to distinguish between the role of meiosis in mosses and
angiosperms.
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Ask students to explain the impacts of mutations that affect the
appearance of flowers.
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Synthesis
Evaluation
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Ask students to explain the possible effects on the different groups of
plants if global climate change were to cause a particular region to
decrease rainfall by half the usual amount.
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Have the students describe the impacts on the different groups of plants if
pesticides are regularly sprayed in an area.
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Ask the students design a hypothetical nature preserve that has the ideal
growing conditions for mosses, ferns, gymnosperms, and angiosperms.
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Ask students evaluate the effectiveness and safety of an herbicide that
inhibits the function of plant vascularature.
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Ask students to evaluate a plan reintroduce extinct plants into an area
where they once grew.
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Ask students to evaluate a plan by a city developer who wants to replace
native gymnosperms with ornamental angiosperms.
VISUAL RESOURCES
It is important to show photographs of the various phyla of plants. Many are quite inconspicuous,
and others are found only in specialized habitats.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Animated Life Cycles.
Introduction
A lecture on plant classification is best supplemented with animations of plant life cycles.
This demonstration provides a visual way of reinforcing the life cycles of the major plant groups.
Materials
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Computer with Shock Wave Media Player and Internet access
LCD hooked up to computer
Web browser linked to the University of Massachusetts Biology website at
http://intro.bio.umb.edu/111-112/112s99Lect/life-cycles.html.
Procedure & Inquiry
1. Review the differences in plant life cycles to students.
2. Load up the animation on Moss Life Cycle.
3. Start the animation and pause it to ask students a question about the event they witnessed.
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4. At the end the animation, ask students to describe particular features of the life cycle.
5. Repeat steps 3 and 4 for the Fern, Gymnosperm, and Angiosperm animations.
6. Ask the students to compare and constrict the plant life cycles.
USEFUL INTERNET RESOURCES
1. Images of plants are available from the University of California at Berkeley CalPhotos:
Plants website. These images are valuable teaching resources for lecture and laboratory
sessions. The site is available at http://calphotos.berkeley.edu/flora/.
2. The Great Plant Escape is useful website that provides plant information students can use
for performing talks to school groups or for giving presentations at nature centers. This
website hosted by the University of Illinois is located at
http://www.urbanext.uiuc.edu/gpe/.
3. The Tree of Life website provides up to date information about plant classification. It has
useful information and images for showing students diversity of plants. The website can
be found at http://tolweb.org/Green_plants/2382.
4. Cases studies are an effective tool for stimulating interest in a lesson on plants. The
University of Buffalo provides a teaching case study called “Torn at the Genes: One
Family's Debate Over Genetically Altered Plants”. It has students investigate issues
genetically modified plants. The case study can be found at
http://ublib.buffalo.edu/libraries/projects/cases/torn_at_the_genes.pdf.
LABORATORY IDEAS
A. A Colorful View of Plant Metabolism
This activity provides students with a visual way to investigate the metabolic processes of
plants using aquatic plants as a model organism. Students are asked to design an experiment that
measures the metabolic processes of plants under dark and light growing conditions.
a. Tell students that they designing an experiment to measure the metabolic processes of
plants under light and dark conditions.
b. Explain to the class that they will be provided with a pH indicator called phenol red as a
way of measuring metabolism. Phenol red is pink under basic conditions, orange under
neutral conditions, and yellow under acidic conditions.
c. Provide students with the following materials
a. Growth solution containing the following chemical composition:
i. 0.01M monobasic sodium phosphate
ii. Solution adjusted to pH 7
b. Test tubes with loose fitting caps as used in microbiology
c. 0.1% solution of phenol red
d. Elodea
e. Euglena
f. Light source
g. Aluminum foil
d. Ask students to research why pH is an indicator of plant metabolism. Give a hint that
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e.
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CO2 affects the pH of a solution.
Instruct students to design two model experiments using elodea and euglena and to
indicate plant metabolism under light and dark growing conditions.
Remind the students to think about the role of controls in the experiment.
This experiment may take 2 to 3 days to collect results
Have the student prepare a report on their findings that can be compared in some format
to the data from the whole class.
B. Life Cycle Issues
This activity has students design and experiment to test the environmental conditions
needed for plant germination. They will use Wisconsin Fast Plant seeds and Fast Fern spores as
a model plant.
i. Tell students that they will be investigating the conditions needed for plant germination.
j. Provide students with the following materials
a. Wisconsin Fast Plant seeds
b. Wisconsin Fast Fern (C-Fern) spores
c. Petri plates with sterile plain agar for Fast Plants
d. Petri plates with sterile C-Fern media for Fast Ferns
e. Forceps
f. Covered plastic containers large enough to place Petri plates
g. Anaerobic pack or generator as used in microbiology
h. Light source
i. Thermometers
j. Small hygrometer (measuring atmospheric moisture)
k. Sterile water
k. Instruct students to design an experiment to test the environmental conditions needed for
plant germination for spores and seeds.
l. Students should plan to take a week to collect their data.
m. Have the students prepare a report explaining the conditions necessary for seed for spore
germination. They should have literature supporting if their findings are consistent with
the conditions needed for all plants seeds or spores
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students do a lesson do a presentation about different types of plants to elementary
school students.
2. Have students perform volunteer service at a nature center.
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3. Have students speak to a civic group about the importance of having plants in cities and
urban areas.
4. Have students work with a local environmental group on plant conservation projects.
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