_____________
CHAPTER 10
Plant Diversity
Chapter Outlines
Introduction
The Life Cycle of Plants
Characteristics of Plants
Importance of Plants
Classification of Plants
Nonvascular Land Plants - Bryophytes
Seedless Vascular Plants - Ferns and Fern Relatives
Vascular Plants with Naked Seeds on Cones - Gymnosperms
Vascular Plants with Seeds Enclosed in a Fruit - Angiosperms
Introduction
Plants (domain Eukarya, kingdom Plantae) are a diverse group of photosynthetic
terrestrial organisms that make life possible by producing food and oxygen, and removing carbon
dioxide from the atmosphere. They range from simple nonvascular plants (bryophytes) to
complex flowering plants (angiosperms). Nonvascular plants include liverworts, mosses, and
hornworts. Vascular plants include seedless and seed-producing plants. Seedless vascular plants
include ferns and fern relatives. Seed-producing plants include gymnosperms and angiosperms.
Gymnosperms are cone-bearing plants and include ginkgoes, cycads, gnetophytes, and conifers.
Angiosperms are flowering plants and include monocots and dicots. Angiosperms are considered
the most advanced and successful plants, possessing vascular tissue with xylem vessels, seeds,
flowers with ovaries, and double fertilization. Out of the nearly 300,000 land plants, 250,000 of
them are angiosperms.
Plants are believed to have evolved from a group of multicellular green algae during the
Silurian period about 330 million years ago. Features shared by both present-day green algae and
plants include: multicellularity; chloroplasts with well-developed grana; chlorophylls a and b and
carotenoids; cellulose-rich cell walls; storage of excess food as starch; plasmodesmata that
interconnect cells; and formation of cell plate during cytokinesis of cell division. Eventually
plants developed cuticle, sporopollenin-walled spores, stomata, conducting tissues, specialized
organs, mycorrhizae, multicellular embryos protected from desiccation by parental tissue, true
lignin, seeds, flowers and fruits, alternation of generations life cycle, and other features that
made them less dependent on free water and were important factors in the overwhelming success
of plants on land.
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The Life Cycle of Plants: Alternation of Generations
During the alternation of generations life cycle of plants, a diploid (2n) sporophyte
generation alternates with a haploid (n) gametophyte generation. The haploid gametophyte
generation produces haploid gametes (sperm and egg) that undergo syngamy to produce a
diploid zygote (2n) that develops into the diploid sporophyte generation. Specific reproductive
tissues on the sporophyte plant divide by meiosis (sporic meiosis) to produce haploid spores that
develop into the gametophyte plants. Nonvascular plants exhibit prominent gametophytes and
reduced, dependent sporophytes. Vascular plants are primarily sporophytic with reduced,
dependent gametophytes.
Seedless vascular plants (ferns) are homosporous, producing one type of spores that
grow into bisexual gametophytes. Seed-producing plants (gymnosperms and angiosperms) are
heterosporous, producing two types of spores: microspores that grow into male gametophytes
and megaspores that grow into female gametophytes.
Characteristics of Plants
Plants, together with fungi and animals, have evolved about 500 million years ago. Since
colonizing land, plants have diversified into roughly 300,000 living species inhabiting all but the
harshest environments, such as some mountaintops and some deserts and polar regions.
The key traits that appear in land plants are: cell wall made of cellulose, cuticle that
covers the entire aerial part of the plant, apical meristem, alternation of generations life cycle,
sporopollenin-walled spores produced in sporangia, stomata for moisture and gas exchange,
multicellular gametangia, embryos and gametes protected by parental tissues, formation of cell
plate during cell division, mycorrhizae, conducting tissues and specialized organs, true lignin,
seeds, flowers and fruits.
Importance of Plants
Plants are the basis of our national and world economy and have a fascinating history and
lore. Plants are dominant photosynthetic organisms on land that make life possible by producing
food and oxygen and removing carbon dioxide from the atmosphere. They affect virtually
everything we do. Consider the following examples.
1.
2.
3.
4.
5.
During photosynthesis, plants produce food and oxygen that sustain life on Earth.
Plants supply our food and many of our drinks.
Our houses are constructed with lumber from trees, which also furnish the cellulose for
paper, cardboard, and synthetic fibers. We use spruce (Picea sp.), a gymnosperm, to
make 23,000 tons of newsprint needed each day to produce 65 million newspapers.
Spruce wood also is especially important to the music industry.
Our clothing, camping equipment, bedding, and other textile goods are made from fibers
of many different plant families. Paper money is made from fibers of flax.
We use extracts from plants and plantlike organisms to make paints, plastics, soap, oils,
adhesives, natural rubber, waxes, dyes, and spices.
2
6.
7.
8.
9.
10.
11.
12.
13.
All medicines and drugs at one time came from plants, fungi, or bacteria; and many
important ones including antibiotics, still do. Drugs such as morphine, cocaine, aspirin,
caffeine, digitoxin, quinine, and vinblastine are extracted from plants.
Natural rubber (caoutchouc) is obtained from the Para rubber tree (Hevea brasiliensis)
and the guayule tree (Parthenium agentatum).
We use flowers and other plant parts for decoration, perfumes, and to express our
feelings.
Coal is fossilized plant material, and oil may have formed from microscopic algae or
animals that were plant consumers.
Plants remove carbon dioxide from the air and help reduce chances of global warming.
Some trees, such as Ginkgo biloba, remove air pollution.
Many houseplants help in removing indoor air pollution.
Bryophytes (liverworts, hornworts, and mosses) contribute significantly to plant
biodiversity. They store large amounts of carbon, thereby playing a significant role in the
global carbon cycle. They are important initial colonizers of bare rock and soil surfaces.
They degrade rocks to soil, stabilize soil, and reduce erosion. Bryophytes are remarkably
sensitive to air pollution, and they are often absent or represented by only a few species
in highly polluted areas. Humans have used bryophytes as a source of fuel, in production
of Scotch whiskey, and as packing materials. Peat moss is used as fuel in many parts of
the world, and also to improve the physical condition of soils, especially sandy soils.
Sphagnum moss is an excellent absorbent of moisture with antiseptic properties. This is
why it is often used in shipping items that must be kept moist. Mosses are also used as
stuffing in furniture and as absorbents in oil spills.
Some plants clog rivers, damage our crops, cause allergies, and poison us.
Classification of Plants
The kingdom Plantae is divided into a number of phyla based on certain characteristics.
Bryophytes (nonvascular plants) are included in three phyla (Hepatophyta, Anthocerophyta,
and Bryophyta); ferns and fern relatives in four phyla (Pterophyta, Psilophyta, Lycophyta,
and Arthrophyta or Sphenophyta); gymnosperms in four phyla (Cycadophyta, Ginkgophyta,
Gnetophyta, and Coniferophyta); and angiosperms in one phylum (Anthophyta).
Bryophytes are the only plants that lack a well-developed vascular system and true roots,
stems, and leaves. Hence bryophytes are called nonvascular plants. Bryophytes are “leafy” or
thalloid plants that most often grow in moist locations. The haploid (n) gametophyte generation
is dominant and the diploid (2n) sporophyte generation is nutritionally dependent on the
gametophyte. The gametophyte plant is attached to the soil by rhizoids. The rhizoids serve only
to anchor the plant, since absorption of water and inorganic ions commonly occurs directly and
rapidly throughout the gametophyte. The sporophyte plant is unbranched and bears a single
sporangium. It is of shorter duration and less conspicuous than the gametophyte plant. The
sporophytes of most bryophytes are homosporous (producing only one type of spore). The most
commonly known bryophytes are liverworts (phylum Hepatophyta), mosses (phylum
Bryophyta), and hornworts (phylum Anthocerophyta). Both mosses and hornworts have stomata
3
which function primarily in the regulation of gas exchange. Although liverworts lack stomata,
they have surface pores that serve a function similar to that of stomata.
Bryophytes reproduce both asexually and sexually. Asexual reproduction is normally by
fragmentation (vegetative propagation) of gametophyte. Another widespread means of asexual
reproduction in liverworts is the production of gemmae in gemmae cups (“splash cups”).
Gemmae cups contain lens-shaped gemmae, which are splashed out of the cup by falling drops
of rain. If a gemma lands in an adequate environment, it can grow into a new gametophyte plant.
Sexual reproduction involves production of gametangia (gamete-producing bodies) called
antheridia and archegonia, often on separate male and female gametophytes, respectively. Most
species of bryophytes are dioecious (having separate male and female gametophyte plants),
while others are monoecious (producing both antheridia and archegonia on the same plant). The
elongated antheridium is commonly stalked and consists of a sterile (cannot produce sperm)
jacket layer that surrounds numerous spermatogenous cells. Each spermatogenous cell forms a
single biflagellated sperm that must swim in water to reach the egg located inside an
archegonium. The archegonia are flask-shaped, with a long neck and a ventor that encloses a
single egg. When the egg is mature, the neck canal cells disintegrate, resulting in a fluid-filled
tube through which sperm swim to the egg. During this period, chemicals are released that
attract the sperm. After fertilization, the zygote remains within the archegonium where it is
nourished by the maternal gametophyte. This form of nutrition is known as matrotrophy (“food
derived from the mother”). The zygote grows into a multicellular embryo, which eventually
develops into the mature sporophyte. The sporophyte produces spores by meiosis in specialized
jacketed structures called sporangia (sing. sporangium). Sporangia in bryophytes are more
highly advanced than the sporangia in some of the algae, in that the jacket protects the
sporangium from dehydration. Since bryophytes are homosporous, they produce one type of
spores that germinate into one type of gametophytes. At maturity, half the gametophyte plants
produce male heads with antheridia, and the other half produce female heads with archegonia.
There are approximately 24,000 species of bryophytes.
Bryophytes contribute significantly to plant biodiversity. They store large amounts of
carbon, thereby playing a significant role in the global carbon cycle. They are important initial
colonizers of bare rock and soil surfaces. They degrade rocks to soil, stabilize soil, and reduce
erosion. Bryophytes are remarkably sensitive to air pollution, and they are often absent or
represented by only a few species in highly polluted areas. Humans have used bryophytes as a
source of fuel, in production of Scotch whiskey, and as packing materials. Peat moss is used as
fuel in many parts of the world, and also to improve the physical condition of soils, especially
sandy soils. Sphagnum moss is an excellent absorbent of moisture with antiseptic properties.
This is why it is often used in shipping items that must be kept moist. Mosses are also used as
stuffing in furniture and as absorbents in soil spills.
Bryophytes include the liverworts (Phylum Hepatophyta), the mosses (Phylum
Bryophyta), and the hornworts (Phylum Anthocerophyta).
Most of the known 6,000 species of liverworts are leafy and very few are thalloid.
Although liverworts lack stomata, they have surface pores for gas exchange. Liverworts are
dioecious and have male and female haploid gametophyte plants. The gametophyte has a
4
photosynthetic upper surface and a lower surface that stores carbohydrates. In some liverworts,
both male and female plants are lobed and resemble the human liver. Liverworts produce their
gametangia in special, stalked structures called archegoniophores and antheridiophores on the
dorsal surface of the thallus. Archegoniophores bear archegonia, and antheridiophores bear
antheridia. Special cells in archegonia and antheridia form eggs and sperm, respectively, by
mitosis. Liverworts include Marchantia, a thalloid liverwort with a flat, ribonlike gametophyte;
and Concephoalum, the snake liverwort.
Mosses have specialized cells called hydroids that conduct water and minerals, and sieve
elements that conduct organic nutrients.
Vascular plants have vascular tissues: xylem and phloem. The xylem transports water and
dissolved minerals from the root to all plant parts, and the phloem transports sucrose and other
organic compounds from leaves to all plant parts. Vascular plants are characterized by having
true roots, stems, and leaves; dominant sporophyte generation; and sporophytes with welldeveloped cuticle and stomata. Vascular plants include ferns, gymnosperms and angiosperms.
Ferns are seedless vascular plants, and gymnosperms and angiosperms are seed-producing
vascular plants. True ferns are included in the phylum Pterophyta with about 11,000 species.
Gymnosperms (from Greek gymnos, naked, and sperma, seed) are cone-bearing plants. They are
included in the phyla Coniferophyta, Cycadophyta, and Ginkgophyta. Angiosperms (from Greek
angion, vessel or container) are flowering plants included in the phylum Anthophyta. Flowering
plants include monocots and dicots. Gymnosperms are the first seed-producing plants to appear
in the fossil record. These plants have ovules and seeds exposed on the surface of female cones.
Living gymnosperms are included in four phyla and 780 species. The most common
gymnosperms are the conifers. Angiosperms have ovules inside an ovary and seeds enclosed by
a fruit. Angiosperms are the most abundant and successful plants with more than 240,000
species. Angiosperms are the only plants with flowers, fruits, xylem vessels, and double
fertilization.
The 240,000 species of angiosperms are divided into two dicots (about 175,000 species)
and monocots (65,000 species). Dicots and monocots differ from each other in many aspects.
Dicots have two cotyledons in the seed, flower parts (sepals, petals, stamens, and carpels) in
fours or fives or multiples of four or five, leaves with petioles and broad blades, taproot system,
and netted leaf venation. Monocot plants have one cotyledon in the seed, flower parts in threes or
multiples of three, leaves with elongated blades and no petioles, parallel leaf venation, and
fibrous root system. The features of these two groups are shown below:
1.
2.
3.
4.
5.
6.
Monotints
Seed with one cotyledon
1.
Floral parts in threes or multiples of threes 2.
Leaves with parallel venation
Fibrous root system
Stem with vascular bundles scattered in
ground tissue
Hypogeous seed germination
3.
4.
5.
6.
5
Dicots
Seed with two cotyledons
Floral parts in fours or fives or
multiples of four or five
Leaves with netted venation
Tap root system
Stem with vascular bundles
forming a ring, pith at center
Epigeous seed germination
7.
Albuminous seeds
7.
6
Exalbuminous seeds
Review Questions
Multiple-choice Questions: Select the most appropriate answer or statement
1.
Plants are believed to have evolved from a group of multicellular aquatic green algae that
resembled an extant group of green algae called the charophyceans. The traits shared by
plants and the charophyceans include cellulose cell walls; peroxisome enzymes;
flagellated, swimming sperm; similar photosynthetic pigments (chlorophylls a and b and
carotenes); and formation of cell plate during cell division. One of the major distinctions
between land plants and the charophyceans is that
A.
only charophyceans have flagellated, swimming sperm
B.
only plants form a cell plate during cytokinesis of cell division
C.
meiosis proceeds at a faster pace in charophyceans than in plants
D.
embryos are not retained within parental tissues in the charophyceans
E.
chlorophyll pigments in charophyceans are different from those in green plants
Answer: D
2.
Comparisons of both nuclear and chloroplast genes from a wide range of plant and algal
species agree with the morphological and biochemical data in pointing to charophyceans,
particularly Chara and Coleochaete, as the closest living relatives of land plants. What
evidence links land plants and charophyceans to a common ancestry?
A.
cellulose cell walls and similar photosynthetic pigments
B.
both accomplish cytokinesis by formation of cell plate
C.
both have flagellated swimming sperm
D.
presence of peroxisome enzymes
E.
all of these are correct
Answer: E
3.
Many species of charophycean algae inhabit shallow waters around the edges of lakes
and ponds, where they are subject to occasional drying. In such environments, natural
selection favors individual algae that can survive periods when they are not submerged in
water. It is likely that the accumulation of certain traits by a population of charophycean
ancestors enabled some of their descendants, the first land plants, to live permanently on
land. Which of the following is an adaptation that enabled the descendants of some
charophyceans to move to land?
A.
sporopollenin-walled spores produced in sporangia
B.
embryos and gametes protected by parental tissues
C.
multicellular gametangia and embryos
D.
cuticle and stomata
E.
all these are correct
Answer: E
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4.
5.
6.
The kingdom Plantae includes embryophytes, plants with embryos. On a field trip, a
marine biology student collects an organism that has differentiated organs, cell walls of
cellulose, and chloroplasts with chlorophyll a. Based on this description, the organism
could be a brown alga, a red alga, a green alga, a charophycean recently washed into the
ocean from a freshwater or brackish water source, or a land plant washed into the ocean.
Which of the following features would definitely identify this organism as a land plant?
A.
presence of alternation of generations
B.
presence of flagellated sperm
C.
presence of sporopollenin
D.
presence of embryos
E.
cellulose cell walls
Answer: D
During the alternation of generations life cycle of plants, a multicellular diploid (2n)
sporophyte produces haploid (n) spores in sporangia by meiosis. The spores germinate
into multicellular gametophytes. The haploid gametophytes produce haploid gametes by
mitosis. The gametes unite during fertilization to produce diploid zygotes. The zygotes
grow into embryos that develop into sporophytes. Which of the following structures is
diploid (2n)?
A.
spore
B.
zygote
C.
gamete
D.
sporophyte
E.
both B and D are correct
Answer: E
The life cycle of plants is called alternation of generations. Some green algae also exhibit
alternation of generations. However, the closest green algal relatives to plants, the
charophyceans, do not exhibit alternation of generations. A characteristic of alternation of
generations unique to plants is the occurrence of meiosis in sporophytes and the
production of haploid spores. Keeping in mind the recent evidence from molecular
systematics, the correct interpretation of these observations is that
A.
alternation of generations cannot be beneficial to charophyceans
B.
charophyceans are not related to either land plants or green algae
C.
plants evolved alternation of generations independently of green algae
D.
plants evolved directly from green algae that perform alternation of generations
E.
scientists have no evidence to indicate whether or not land plants evolved from
any kind of green algae
Answer: C
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7.
Land plants are divided into two groups based on the presence or absence of a system of
vascular tissue, cells joined into tubes that transport water and food throughout the plant
body. Most plants have a complex vascular tissue system and are therefore called
vascular plants. Plants that do not have a vascular tissue system are called nonvascular
plants or bryophytes. Out of the 10 phyla of extant plants, which phylum includes
nonvascular plants?
A.
Bryophyta
B.
Hepatophyta
C.
Anthocerophyta
D.
A and B are correct
E.
A, B, and C are correct
Answer: E
8.
Bryophytes are the only plants that lack a well-developed conducting or vascular system;
hence they are called nonvascular plants. These plants include liverworts, hornworts and
mosses. Unlike vascular plants, in all three bryophyte groups the gametophytes are larger
and longer-living than the sporophytes. There are approximately 24,000 species of
bryophytes. Bryophytes have all of the following characteristics except
A.
gametes enclosed in multicellular protective structures
B.
biflagellated sperm that require water to reach the egg
C.
sporopollenin-walled spores in sporangia
D.
dominant gametophyte generation
E.
lignified vascular tissues
Answer: E
9.
When moss spores germinate, they develop into branched filaments known as
protonemata (singular, protonema). A protonema has a large surface area that enhances
absorption of water and minerals. In favorable conditions, a protonema produces one or
more “buds,” each with an apical meristem that generates a gamete-producing structure
known as a gametophore. Together, a protonema and a gametophore make up the body of
a moss gametophyte. Which of the following is a function of a moss gametophyte?
A.
production of sperm in antheridia
B.
production of eggs in archegonia
C.
production of food by photosynthesis
D.
only A and B are correct
E.
A, B, and C are correct
Answer: E
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10.
Bryophyte gametophytes do not grow tall because they lack vascular tissues, which are
required for long-distance transport of water and food. The thin structure of bryophyte
organs makes it possible to distribute materials without specialized vascular tissue.
However, some mosses, including the genus Polytrichum, have conducting tissues in the
center of their “stems,” and a few of these mosses can grow as tall as 2 m as a result. The
gametophytes are anchored to the soil by delicate rhizoids, which are long, tubular single
cells (in liverworts and hornworts) or filaments of cells (in mosses). Unlike roots, which
are characteristic of vascular plants, rhizoids
A.
do not play a primary role in water and mineral absorption
B.
lack specialized conducting cells
C.
are not composed of tissues
D.
both A and B are correct
E.
A, B, and C are correct
Answer: E
11.
In bryophytes, mature gametophytes produce gametes in multicellular gametangia
covered by protective tissue. A gametophyte may have multiple gametangia. Eggs are
produced singly in archegonia, whereas antheridia each produce many sperm. Some
gametophytes are bisexual, but in mosses the archegonia and antheridia are typically
carried on separate female and male gametophytes. Flagellated sperm swim through a
film of water toward eggs, entering the archegonia in response to chemical attractants.
Eggs are not released but instead remain within the bases of archegonia. After
fertilization, embryos are retained within the archegonia. Which of the following
statements is true of archegonia?
A.
they are the sites where female gametes are produced
B.
they may temporarily contain young sporophytes
C.
they are the ancestral versions of animal ovaries
D.
they are asexual reproductive structures
E.
both A and B are correct
Answer: E
12.
In the moss Polytrichum, the sporophyte is small and simple, and is dependent on the
female gametophyte for water, food and support. A typical sporophyte consists of a foot,
a seta (stalk), and a sporangium called a capsule. Embedded in the archegonium, the foot
absorbs nutrients from the female gametophyte. The seta conducts these materials to the
capsule, which uses them to produce spores by meiosis. One capsule can generate up to
50 million spores. The discharge of spores and their subsequent dispersal are enhanced by
which of the following features?
A.
a capsule has a peristome that is specialized for gradual spore discharge
B.
an elongated seta enhances spore dispersal by elevating the capsule
C.
insect pollinators that open the capsule to feed on nectar
D.
both A and B are correct
E.
A, B, and C are correct
Answer: D
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13.
The two generations in the life cycle of a moss are the gametophyte and the sporophyte.
The gametophyte is haploid (n) and produces haploid gametes by mitosis. The
sporophyte is diploid (2n) and produces haploid spores by meiosis. The sporophyte is
dependent on the gametophyte for nourishment and support. Which of the following
statements about moss sporophytes is correct?
A.
a sporophyte is composed of foot, seta, and capsule
B.
the foot absorbs nutrients from the gametophyte
C.
the seta conducts nutrients to the capsule
D.
the capsule produces spores by meiosis
E.
all of these are correct
Answer: E
14.
Bryophytes include liverworts, mosses, and hornworts. Moss and hornwort sporophytes
are larger and more complex than those of liverworts. Both moss and hornwort
gametophytes also have stomata, which support photosynthesis by regulating the
exchange of CO2 and O2 between the outside air and the gametophyte interior. Stomata
also play a major role in water regulation. Liverworts lack stomata and have surface
pores, instead. Which of the following is a correct statement about the different types of
bryophytes?
A.
the female gametophyte bears multiple sporophytes in liverworts and hornworts,
and a single sporophyte in mosses
B.
the sporophyte has a short seta in liverworts and a long seta in hornworts and
mosses
C.
the gametophyte has stomata in hornworts and mosses, and surface pores in
liverworts
D.
both A and B are correct
E.
A, B, and C are correct
Answer: E
15.
Mosses are nonvascular land plants included in the phylum Bryophyta. These plants are
characterized by a dependent sporophyte and a protonema stage in their life cycle. The
sporophyte produces one type of spores that germinate into protonemata (singl.
protonema) that develop into gametophytes. At a certain stage of development, 50
percent of the gametophyte plants produce male heads with antheridia and the other 50
percent produce female heads with archegonia. Which of the following is an example of
how structure fits function in mosses?
A.
the vase-shaped archegonia protect eggs and transport nutrients to the embryo
B.
large surface area of protonemata enhances absorption of water and minerals
C.
stomata enable CO2/O2 exchange while minimizing water loss
D.
peristomes enable gradual spore discharge
E.
all of these are correct
Answer: E
11
16.
How do bryophytes differ from other plants?
A.
bryophytes are described as nonvascular because they do not have an extensive
transport system
B.
the life cycle of bryophytes is dominated by gametophyte generation rather than
sporophyte generation
C.
bryophytes have unicellular gametangia and do not protect their gametes and
embryos by parental tissue
D.
both A and B are correct
E.
A, B, and C are correct
Answer: D
17.
Vascular plants have two types of vascular tissues: xylem and phloem. The xylem of all
vascular plants includes tracheids that carry water and minerals up from roots. Because
all vascular plants have tracheids, they are sometimes referred to as tracheophytes.
Among vascular plants, only angiosperms (flowering plants) have vessel elements (xylem
vessels) beside tracheids in their xylem tissue. The water-conducting cells in vascular
plants are lignified; that is, their cell walls are strengthened by the phenolic polymer
lignin. The phloem tissue transports sugars, amino acids, and other organic products.
How did lignified vascular tissues contribute to the success of vascular plants?
A.
permitted vascular plants to grow to greater heights than bryophytes
B.
stems could transport water and nutrients high above the ground
C.
stems became strong enough to withstand drooping
D.
both A and B are correct
E.
A, B, and C are correct
Answer: E
18.
Seedless vascular plants include true ferns and fern relatives (fern allies). True ferns are
included in the phylum Pterophyta. Fern relatives are included in the phyla: Lycophyta
(club mosses, spike mosses and quillworts); Sphenophyta (horsetails); and Psilotophyta
(whisk ferns). The key characteristics that distinguish seedless vascular plants from
bryophytes are: a sporophyte-dominant life cycle; the presence of xylem and phloem;
branched sporophytes; and the evolution of true roots and leaves. Seedless vascular plants
have swimming sperm and fragile independent gametophytes. A botanist discovers a new
plant species in a tropical rain forest. After observing its anatomy and life cycle, the
following characteristics are noted: flagellated sperm, xylem with tracheids, separate
gametophyte and sporophyte generations, and no seeds. This plant is probably a
A.
flowering plant
B.
gymnosperm
C.
liverwort
D.
moss
E.
fern
Answer: E
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19.
The conducting cells of the phloem tissue include
A.
sieve-tube members
B.
companion cells
C.
vessel elements
D.
tracheids
E.
both A and B are correct
Answer: A
20.
A major change that occurred during the evolution of plants from their algal ancestors
was the origin of a branched sporophyte. This derived characteristic first appeared in the
seedless vascular plants, such as ferns. What advantage would branched sporophytes
provide to the plant?
A.
increased potential for independence of sporophyte from gametophyte
B.
increased size of the sporophyte generation
C.
increased rate of fertilization
D.
increased gamete production
E.
increased spore production
Answer: E
21.
Most seedless vascular plants are homosporous, and produce one type of spore that
typically develops into a bisexual gametophyte. In contrast, seed-producing vascular
plants (gymnosperms and angiosperms) are heterosporous, and produce two kinds of
spores, megaspores which develop into female gametophytes and microspores which
develop into male gametophytes. If the gametophyte of a plant is bisexual, then the plant
A.
must be diploid
B.
belongs to a homosporous species
C.
belongs to a heterosporous species
D.
has lost the need for a sporophyte generation
E.
has antheridia and archegonia combined into a single sex organ
Answer: B
22.
Which of the following plants is described as vascular and homosporous?
A.
Polypodium, a fern
B.
Polytrichum, a moss
C.
Pinus, a gymnosperm
D.
Marchantia, a liverwort
E.
Helianthus, an angiosperm
Answer: A
23.
Which of the following plants is described as vascular and heterosporous?
A.
Polypodium, a fern
B.
Polytrichum, a moss
C.
Pinus, a gymnosperm
D.
Anthoceros, a hornwort
E.
Marchantia, a liverwort
Answer: C
13
24.
During the Carboniferous Period (360-286 million years ago), the dominant plants on
Earth were giant lycophytes, horsetails, and ferns, forming the “coal forests.” Those were
the plants that formed the coal deposits of the present time. At the time when dinosaurs
were the dominant animals, gymnosperms were the dominant plants. At the present time,
the dominant plants are
A.
angiosperms
B.
mosses
C.
cycads
D.
ferns
E.
pine
Answer: A
25.
Which of the following types of plants would have been present in the forests that
became the coal deposits of today?
A.
ferns
B.
fern relatives
C.
angiosperms
D.
gymnosperms
E.
both A and B are correct
Answer: E
26.
Seed plants include gymnosperms and angiosperms. Gymnosperms are included in four
phyla: Ginkgophyta (ginkgo), Cycadophyta (cycads), Gnetophyta (gnetophytes), and
Coniferophyta (conifers). Angiosperms are included in the single phylum Anthophyta
(flowering plants). Which of the following features contributed to the enormous success
of seed plants on land?
A.
highly reduced gametophytes that are nurtured and protected in ovules and pollen
grains
B.
pollen grains with tough protective coats that facilitate transfer of sperm without
reliance on water
C.
seeds, which are more resilient than spores, protect embryos and facilitate wider
distribution
D.
both A and B are correct
E.
A, B, and C are correct
Answer: E
14
27.
Seed plants have had an enormous impact on human society. Starting about 13,000 years
ago, humans began to domesticate wheat, maize, bananas, and other wild seed plants.
This practice emerged separately in various regions of the world, including the Near East,
East Asia, Africa, and the Americas. The domestication of seed plants, particularly
angiosperms, produced the most important cultural change in human history,
transforming most human societies from roving bands of hunter-gatherers to permanent
settlements anchored by agriculture. Over human history, which process has been most
important in improving the quality of plants that have long been used by humans as staple
foods?
A.
pesticide and herbicide application
B.
genetic engineering
C.
artificial selection
D.
natural selection
E.
sexual selection
Answer: C
28.
Seed plants are heterosporous and have ovules, pollen, and reduced gametophytes. A
seed is a mature ovule, which consists of an embryo, along with a food supply, packaged
within a protective coat derived from the integuments of the ovule. Until the advent of
seeds, the spore was the only protective stage in any plant life cycle. Which of the
following is not correct about seeds?
A.
seeds have dormancy which helps young sporophytes to avoid dry seasons
B.
seeds are multicellular structures more resistant and complex than spores
C.
seeds enable plants to better resist harsh environments
D.
seeds help plants disperse offspring more widely
E.
seeds are mature ovaries
Answer: E
29.
In addition to seeds, the following adaptations are common to all seed plants: reduced
gametophytes, heterospory, ovules, and pollen. While the gametophytes of seedless
vascular plants are visible to the naked eye, the gametophytes of seed plants are mostly
microscopic. Which of the following is an advantage of a reduced gametophyte?
A.
tiny gametophytes can develop from spores retained within the sporangia of the
parental sporophyte
B.
moist reproductive tissues of the parental sporophyte protect gametophytes and
shield them from drought conditions and from UV radiation
C.
dependent gametophytes can easily obtain nutrients from the parental sporophyte
D.
only A and B are correct
E.
A, B, and C are correct
Answer: E
15
30.
Nearly all seedless vascular plants are homosporous (produce one kind of spore) and
usually give rise to bisexual gametophytes. On the other hand, seed plants are
heterosporous: Megasporangia in megasporophylls produce megaspores that give rise to
female gametophytes, and microsporangia in microsporophylls produce microspores that
give rise to male gametophytes. Each megasporangium has a single functional
megaspore, whereas each microsporangium contains vast numbers of microspores. A
megaspore develops into a female gametophyte within an ovule, and a microspore
develops into a male gametophyte in a pollen grain. Where in an angiosperm would you
find a megasporangium?
A.
within an ovule contained within an archegonium of the female gametophyte
B.
packed into pollen sacs within the anthers found on a stamen
C.
within an ovule contained within an ovary of a flower
D.
enclosed in the stigma of a flower
E.
in the style of a flower
Answer: C
31.
Gymnosperms include ginkgo (phylum Ginkgophyta), cycads (phylum Cycadophyta),
gnetophytes (phylum Gnetophyta) and conifers (phylum Coniferophyta). These plants are
called gymnosperms because they produce naked seeds on cones or strobili. In contrast,
angiosperms (phylum Anthophyta) produce seeds enclosed in fruits. Among the
gymnosperms are conifers, which include such trees as pines, firs, and redwoods. Which
of the following statements is generally correct of conifers?
A.
consist of about 575 species of trees, many evergreen
B.
include pines, spruces, firs, cedars, hemlocks, redwoods, cypresses, yews, and
junipers
C.
the coastal redwood (Sequoia sempervirens) is the tallest living plant
D.
the bristlecone pine (Pinus longaeva) is the oldest living tree, one is 4,900 years
old
E.
all of these are correct
Answer: E
32.
Angiosperms are flowering plants included in the phylum Anthophyta. These are the
most readily recognized and the most abundant and diverse plants. Angiosperms are the
only group of plants with seeds, fruits, flowers, ovaries, vessel elements and double
fertilization. At pollination, their ovules are encased within the ovary of the carpel.
Angiosperms undergo double fertilization where one sperm nucleus fuses with the egg to
produce the diploid zygote (2n) while a second sperm nucleus fuses with two polar nuclei
to form the nutritive triploid (3n) endosperm. After fertilization, the ovule develops into
the seed and the ovary develops into the fruit. The success of angiosperms is due to
A.
highly efficient xylem with vessel elements
B.
reduced gametophytes
C.
fruits enclosing seeds
D.
animal pollination
E.
all of these
Answer: E
16
33.
Plants remove CO2 from the air and give off O2 during the process of photosynthesis. In
1850, atmospheric CO2 was about 280 parts per million (ppm), and today it is about 350
ppm. The increase is largely due to the burning of wood and fossil fuels and the
destruction of tropical forests. Other gases emitted due to human activities include nitrous
oxide (N2O) from fertilizers and animal wastes and methane (CH4) from bacterial
decomposition. These gases are known as greenhouse gases and are contributing
significantly to the rise in Earth’s ambient temperature, a phenomenon called global
warming. Which of the following is a valid argument for preserving tropical forests?
A.
plants remove CO2 from the air, a gas that contributes to global warming
B.
plants that are possible sources of food and medicine are being lost
C.
clearing land for agriculture results in soil erosion
D.
many organisms are becoming extinct
E.
all of these are correct
Answer: E
34.
Which of the following structures is not found in angiosperms?
A.
triploid endosperm tissue
B.
flagellated sperm
C.
xylem vessels
D.
flowers
E.
fruits
Answer: B
35.
Double fertilization is unique to angiosperms. During this process, one sperm cell unites
with the egg to form a diploid (2n) zygote, and a second sperm cell unites with the two
polar nuclei to produce a triploid (3n) endosperm nucleus. Hypothetically, one of the
benefits of double fertilization is to
A.
coordinate developmental timing between the embryo and its food stores
B.
increase the number of fertilization events and offspring produced
C.
emphasize embryonic survival by increasing embryo size
D.
promote diversity in flower shape and color
E.
both A and B are correct
Answer: A
36.
A flower is an angiosperm structure specialized for sexual reproduction. It is a
specialized shoot that can have up to four rings of modified leaves called floral organs:
sepals (calyx), petals (corolla), stamens (androecium), and carpels (gynoecium). Which
of the following statements is correct of a flower carpel?
A.
surrounds and nourishes the female gametophyte
B.
is a feature of the sporophyte generation
C.
consists of highly modified sporophylls
D.
consists of stigma, style, and ovary
E.
all of these are correct
Answer: E
17
37.
Angiosperms are divided into two major groups: Monocots and dicots. Monocots are
characterized by seeds with one cotyledon, flower parts in 3 or multiples of 3, parallel
leaf venation, fibrous root system, and leaves without petioles. Which of the following
statements is not true of dicots?
A.
together with monocots, they are included in the phylum Anthophyta
B.
their floral parts are in 3 or multiples of 3
C.
they possess seeds with two cotyledons
D.
the veins of their leaves are netted
E.
they have taproot systems
Answer: B
18
True/False Questions. If the answer is “True,” learn the scientific fact presented in the
question. If the answer is “False,” find why it is false, and learn the correct scientific fact
presented in the question.
38.
The most recent common ancestor of all land plants was most similar to modern-day
charophyceans
Answer: True
39.
Spores of land plants are covered with a thick coating made of sporopollenin
Answer: True
40.
Alternation of generations life cycle does not provide evidence for a close evolutionary
relationship between charophyceans and members of the plant kingdom.
Answer: True
41.
Members of the plant kingdom are known as embryophytes.
Answer: True
42.
Antheridia may temporarily contain sporophyte embryos.
Answer: False
43.
Both male and female bryophytes produce archegonia.
Answer: False
44.
Bryophytes are characterized by having vascular tissues.
Answer: False
45.
A dissection of the interior of the stem of an angiosperm should reveal lignified vascular
tissues.
Answer: True
46.
Chloroplast is a characteristic shared by algae and seed plants.
Answer: True
47.
Angiosperms (phylum Anthophyta) are the only plants with flowers and fruits.
Answer: True
48.
Gymnosperms have both tracheids and vessel elements in their xylem tissue.
Answer: False
19
Fill-in-the blank Questions: Use word bank below
lycophytes
protonema
tracheids
sporophylls
double fertilization
monocots
pterophytes
peristome
xylem
homosporous
pistil
eudicots
bryophytes
calyptra
phloem
heterosporous
embryo sac
fruit
embryophytes
megaphylls
microphylls
pollination
endosperm
seed
49.
A __________ is a mature ovule.
Answer: seed
50.
A __________ is a mature ovary.
Answer: fruit
51.
A clade consisting of the vast majority of flowering plants that have seeds with two
cotyledons is called __________.
Answer: eudicots
52.
Angiosperms with parallel leaf venation and floral parts in 3 or multiples of 3 are called
__________.
Answer: monocots
53.
During __________ __________, one sperm unites with the egg to form the zygote, and
a second sperm unites with the two polar nuclei to form the endosperm nucleus.
Answer: double fertilization
54.
A single carpel or a group of fused carpels is sometimes called a __________.
Answer: pistil
55.
In angiosperms, a mature female gametophyte is called __________ __________.
Answer: embryo sac
56.
The triploid nucleus of the central cell of the female gametophyte divides repeatedly and
develops into __________, tissue rich in starch and other food reserves.
Answer: endosperm
57.
__________ are modified leaves that carry sporangia.
Answer: sporophylls
58.
Most seedless vascular plants are __________, having one type of sporophyll producing
one type of spore that typically develops into a bisexual gametophyte.
Answer: homosporous
A __________ plant has two types of sporophylls and produces two kinds of spores.
Answer: heterosporous
59.
20
60.
The transfer of pollen from the anthers of the stamen to the stigma of the carpel is called
__________.
Answer: pollination
61.
__________ are long, tapered water-conducting cells that are dead at maturity and are
found in the xylem of all vascular plants.
Answer: tracheids
62.
The vascular tissue that conducts water and minerals is the __________.
Answer: xylem
63.
The vascular tissue that conducts sugars and other organic compounds is the
__________.
Answer: phloem
64.
All lycophytes have __________, small, usually spine-shaped leaves with a single vein.
Answer: microphylls
65.
Ferns and seed plants have __________, leaves with a highly branched vascular system.
Answer: megaphylls
66.
Germinating moss spores produce a mass of green, branched, one-cell-thick filaments
known as a __________.
Answer: protonema
67.
In most moss species, the upper part of the capsule (sporangium) features a ring of
toothlike structures known as the __________.
Answer: peristome
68.
An immature capsule (sporangium) of a moss has a protective cap of gametophyte tissue
called the __________.
Answer: calyptra
69.
Club mosses and their relatives are known as __________.
Answer: lycophytes
70.
The members of the phylum Pterophyta that include ferns and their relatives are called
__________.
Answer: pterophytes
71.
All land plants are called __________ because they share the common trait of
multicellular, dependent embryos.
Answer: embryophytes
21
Concept Questions and Answers
72.
Explain the economic and ecological significance of plants
Plants are the basis of our national and world economy and have a fascinating history and
lore. Plants are dominant photosynthetic organisms on land that make life possible by
producing food and oxygen. They affect virtually everything we do. Consider the
following examples.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
73.
During photosynthesis, plants produce food and oxygen that sustain life on
Earth.
Our houses are constructed with lumber from trees, which also furnish the
cellulose for paper, cardboard, and synthetic fibers. We use spruce (Picea
sp.), a gymnosperm, to make 23,000 tons of newsprint needed each day to
produce 65 million newspapers. Spruce wood also is especially important
to the music industry.
Our clothing, camping equipment, bedding, and other textile goods are
made from fibers of many different plant families. Paper money is made
from fibers of flax.
We use extracts from plants and plantlike organisms to make paints,
plastics, soap, oils, adhesives, natural rubber, waxes, dyes, and spices.
All medicines and drugs at one time came from plants, fungi, or bacteria;
and many important ones including antibiotics, still do. Drugs such as
morphine, cocaine, aspirin, caffeine, digitoxin, quinine, and vinblastine are
extracted from plants.
Natural rubber (caoutchouc) is obtained from the Para rubber tree (Hevea
brasiliensis) and the guayule tree (Parthenium agentatum).
Some plants clog our rivers, damage our crops, cause allergies, and poison
us.
We use flowers and other plant parts for decoration, perfumes, and to
express or feelings.
Coal is fossilized plant material, and oil may have formed from
microscopic algae or animals that were plant consumers either directly or
indirectly.
Plants remove carbon dioxide from the air and help reduce chances of
global warming. Some trees, such as Ginkgo biloba, remove air pollution.
Many houseplants help in removing indoor air pollution.
Describe the evidence linking land plants to a charophycean ancestry
There are four traits that land plants share only with the charophyceans, suggesting a
close relationship between the two groups:
1.
rosette (rose-shaped) complexes for cellulose synthesis
2.
peroxisome enzymes
3.
structure of flagellated sperm
4.
synthesis of cell plates during cell division involves formation of phragmoplasts
22
74.
What adaptations, especially those associated with dependence upon free water,
were necessary for plants to become dominant terrestrial organisms?
The key adaptations associated with dependence upon free water include:
1.
Sporopollenin-walled spores produced in sporangia
2.
epidermis covered with cuticle that consists of polyesters and waxes. The cuticle
acts as waterproofing, helping prevent excess water loss from the above-ground
organs
3.
stomata reduce water loss
4.
embryos and gametes protected by parental tissues
5.
pollen tube that protects sperm and delivers it to the egg
6.
reduced gametophyte protected by sporophyte from drying up
7.
mycorrhizae increase root surface area and allow for more water absorption
8.
conducting tissues and specialized organs
9.
seeds protect embryo from desiccation
75.
List the ten phyla of extant plants. Give common names, genus name, and number
of species.
________________________________________________________________________
Phylum
common name
genus name
No. of species
________________________________________________________________________
Hepatophyta
liverworts
Marchantia
9,000
Anthocerophyta
hornworts
Anthoceros
100
Bryophyta
mosses
Polytrichum
15,000
Lycophyta
lycophytes
Selaginella
1,200
Pterophyta
pterophytes
Polypodium
12,000
Ginkgophyta
ginkgo
Ginkgo biloba
1
Cycadophyta
cycads
Cycas
130
Gnetophyta
gnetophytes
Welwitschia, Ephedra
75
Coniferophyta
conifers
Pinus
600
Anthophyta
flowering plants
Zea, Helianthus
250,000
________________________________________________________________________
76.
Give examples of how structure fits function in bryophytes.
1.
2.
3.
4.
5.
6.
7.
large surface area of protonema enhances absorption of water and minerals
vase-shaped archegonia protect eggs during fertilization and transport nutrients to
the embryo via placental transfer cells
stalklike seta conducts nutrients from the gametophyte to the capsule
(sporangium) where spores are produced
the peristome enables gradual spore discharge
stomata enable CO /O exchange while minimizing water loss
lightweight spores are wind-dispersed
mosses can lose water without drying and rehydrate when moisture is available
23
77.
How do bryophytes differ from other plants?
1.
2.
78.
Bryophytes lack an extensive transport system (nonvascular)
Life cycle of bryophytes is dominated by gametophytes rather than sporophytes
List some of the key differences between seedless vascular plants and bryophytes.
A sporophyte-dominant life cycle, the presence of xylem and phloem, and the evolution
of true roots and leaves.
79.
What features contributed to the enormous success of seed plants as compared to
seedless plants?
1.
2.
3.
80.
reduced gametophytes of seed plants are nurtured by sporophytes and protected
from stress, such as drought conditions and UV radiation
pollen grains have tough protective coats and can be carried long distances,
facilitating widespread sperm transfer without reliance on water
seeds are more resilient than spores, enabling better resistance to environmental
stresses and wider distribution.
Contrast sperm delivery in seedless vascular plants with sperm delivery in seed
plants.
To have any chance of reaching the eggs, the flagellated sperm of seedless vascular
plants must rely on swimming through a film of water, usually limited to a range of less
than a few centimeters. In contrast, the sperm of seed plants are produced within durable
pollen grains that can be carried long distances by wind or animal pollinators. Although
flagellated in some species, the sperm of most seed plants do not require water because
pollen tubes convey them directly to the eggs.
81.
Explain how the pine life cycle reflects basic characteristics of seed plants.
The pine life cycle illustrates heterospory, as ovulate cones produce megaspores and
pollen cones produce microspores. The reduced gametophytes are evident in the form of
the microscopic pollen grains and the microscopic female gametophyte within the
megaspore. The egg develops within an ovule, and the pollen tube conveys the sperm to
the ovules within the archegonium. The life cycle also shows the protective and nutritive
features of a seed.
82.
Compare and contrast a pine cone and a flower in terms of structure and function.
Pine cones and flowers both have sporophylls, modified leaves that produce spores. Pine
trees have separate pollen cones (with pollen grains) and ovulate cones (with ovules
inside cone scales). In flowers, pollen grains are produced by the anthers of stamens, and
ovules are within the ovaries of carpels. Unlike pine cones, many flowers produce both
pollen and ovules.
24