Answers to Mastering Concepts Questions
16.1
1. How have plants changed the landscape, and how are they vital to life today?
Plants have changed the landscape on Earth by settling on land, providing the base of
most food webs, and providing habitats for animals, fungi, and other organisms. Their
decomposing tissues provide nutrients for organisms that live in leaf litter and enrich
watery habitats like lakes and streams. Plants also changed the atmospheric levels of
carbon dioxide and O2. Plants are vital to life today for all of the same reasons.
2. What evidence suggests that plants evolved from green algae?
Photosynthetic pigments such as chlorophyll a, use of starch as a storage carbohydrate,
cell walls made of cellulose, and similar life cycles that feature alternation of generations
are the features shared by green algae and plants.
3. What are the functions of the cuticle and stomata?
The cuticle is a waxy coating that protects the plant from drying out. The stomata are
pores in the leaf that allow for gas exchange.
4. How does vascular tissue adapt plants to land?
Vascular tissue transports water and nutrients throughout the bodies of plants. Vascular
tissue allows plants to grow tall and distributes water and nutrients throughout the plant
body.
5. Describe the reproductive adaptations of plants.
There are several reproductive adaptations in plants. The first is the ability to alternate
life cycle stages between a diploid (sporophyte) and multicellular haploid stage
(gametophyte). Related to this adaptation is the evolutionary trend to increase the size
and independence of the sporophyte. Pollen is an adaptation that allows reproduction to
occur over great distances and in the absence of free water. Seeds allow for a dormancy
stage and provide food for the developing embryo. Flowers promote efficient pollination,
and fruits aid in seed protection and dispersal.
6. What features differentiate the four major groups of plants?
The presence or absence of swimming sperm, vascular tissue, pollen, seeds, flowers, and
fruits differentiate the four major groups of plants.
16.2
1. Describe the three main groups of bryophytes.
Liverworts have flattened, lobed bodies that lack stems. Hornworts have tapering pointed
sporophytes and flat gametophytes. Mosses are small bryophytes with compact bodies
and structures resembling stems and leaves.
2. Name two reasons mosses usually live in moist, shady habitats.
Mosses occur more frequently in moist, shady habitats because they lack vascular tissue
and because they must be covered by a film of water for sexual reproduction to occur.
3. How do bryophytes reproduce?
Bryophytes reproduce sexually by forming swimming sperm and egg cells within tissues
of separate haploid male and female gametophytes. Conveyed in a droplet of water,
sperm swim to the egg cells. The fertilized egg develops into the diploid sporophyte,
which grows a sporangium in which spore mother cells undergo meiosis to produce
haploid spores. These grow into haploid gametophytes that will differentiate into male
and female plants.
16.3
1. Describe the four groups of seedless vascular plants.
The four groups of seedless vascular plants are:
- club and spike mosses, which have reproductive structures that look like clubs or
spikes;
- whisk ferns, which have rhizomes but lack roots and leaves;
- horsetails, which have branched rhizomes and stems that bear spores at their tips;
- true ferns, which have fronds that grow from rhizomes and spores on the undersides of
the fronds.
2. How do seedless vascular plants reproduce?
Seedless vascular plants reproduce sexually. A sporophyte, such as a fern frond, releases
haploid spores that germinate and develop into gametophytes. Different places on the
gametophyte have egg- and sperm-producing structures. Sperm swim to an egg, and
fertilization takes place. The fertilized egg develops into a diploid sporophyte.
3. How are seedless vascular plants similar to and different from bryophytes?
Both are tied to water by their swimming sperm that require water to reach eggs. Neither
group has pollen, seeds, flowers, or fruits. Seedless vascular plants, however, have xylem
and phloem, which bryophytes lack.
16.4
1. What are the characteristics of gymnosperms?
The characteristics of gymnosperms include vascular tissue, pollen, and naked seeds that
are not enclosed in fruits.
2. What are the four groups of gymnosperms?
The four groups of gymnosperms are cycads, ginkgos, conifers, and gnetophytes.
3. What is the role of cones in conifer reproduction?
Meiosis, pollination, and fertilization occur inside the cone. The gametophyte generation
is also produced within cones.
4. What happens during and after pollination in gymnosperms?
During pollination, a pollen grain is delivered to a female gametophyte. The pollen grain
germinates, forming a pollen tube that grows into the ovule, toward the egg cell. During
fertilization, a haploid sperm nucleus unites with the haploid egg cell, producing a zygote
that will grow into the sporophyte generation.
16.5
1. What are the two largest groups of angiosperms?
The eudicots and monocots are the two largest clades.
2. In what ways are the life cycles of angiosperms similar to and different from those of
conifers?
Similarities include the conspicuous sporophyte stage and the presence of pollen.
However, unlike conifers, the angiosperms produce flowers and fruit. The other major
difference is the production of the endosperm, which provides nutrients for the
developing embryo.
3. What is the relationship between flowers and fruits?
The flowers are the structures that produce pollen and egg cells. After fertilization occurs
in the ovary, parts of the flower develop into the fruit, which encloses the seeds.
4. Describe two ways animals participate in angiosperm reproduction and dispersal?
When searching for food, animals pick up pollen from one plant and transfer it to the next
plant they feed on. In this way they cross fertilize the plants. Animals also disperse fruits
and seeds to new habitats.
16.6
1. Why do researchers collect DNA from permafrost?
The permafrost can contain preserved DNA from ancient plants and animals, allowing
researchers to reconstruct the ancient ecosystem.
2. What are some hypotheses for why the researchers failed to recover any DNA from
sediments that were more than 300,000 to 400,000 years old? How would you test your
hypotheses?
One example of a hypothesis would be that even in the permafrost, DNA erodes after
300,000 to 400,000 years. One way to test this would be to go to other areas known to
have life 300,000 to 400,000 years ago, take core samples, and see if DNA appears in any
of the samples.
Answers to Write It Out Questions
1. What characteristics do all land plants have in common?
All land plants are photosynthetic, multicellular organisms with eukaryotic cells,
cellulose cell walls, and starch as a carbohydrate storage material.
2. How are terrestrial habitats different from aquatic habitats? List the adaptations that
enable plants to obtain resources, transport materials, and reproduce; explain how each
adaptation contributes to reproductive success on land.
In terrestrial environments the nutrients are either in the ground (requiring a root system)
or in the atmosphere (requiring stomata). Also, since the plants aren't surrounded by
water, they are in danger of losing water to their environment; terrestrial habitats,
therefore, have selected for a cuticle. Many plants contain a vascular system that
transports nutrients, water, and sugars between roots and stems, allowing for large plant
size. Pollen allows fertilization to take place without the aid of water. Seeds and fruits
improve reproductive success by protecting the offspring and providing for their
dispersal.
3. Give at least two explanations for the observation that bryophytes are much smaller
than most vascular plants. How can increased height be adaptive? In what circumstances
is small size adaptive?
One explanation is that bryophytes lack vascular tissue, so they lack the support
necessary for large size. Another is that the sperm must swim from one individual to the
next. Increased height can be adaptive in the competition for light. Small size can be
adaptive if it allows for rapid development to reproductive maturity.
4. How do the adaptations of gymnosperms and angiosperms enable them to live in drier
habitats than bryophytes and seedless vascular plants?
Pollen enables plants to reproduce in the absence of free water; seeds protect the embryo
(young sporophyte) until conditions are optimal for germination and growth.
5. How do angiosperms differ from gymnosperms? How are the two groups of plants
similar?
Angiosperms have flowers that produce pollen and egg cells; in gymnosperms, cones
produce pollen and egg cells. Another difference is that angiosperms produce their seeds
in fruits, whereas gymnosperms produce “naked” seeds. Similarities include vascular
tissue, pollen, seeds, and the dominant sporophyte generation.
6. Compare and contrast the life cycles of the four groups of plants. How does each group
represent a variation on the theme of alternation of generations?
All four groups of plants produce haploid gametophytes and diploid sporophytes, but the
relative sizes of these structures can vary. In bryophytes, the gametophyte is relatively
large and carries out photosynthesis; the sporophyte can be small and depends on the
gametophyte for nutrition. In seedless vascular plants, the gametophyte carries out
photosynthesis, but it is very small and is quickly dwarfed by the growing sporophyte. In
gymnosperms and angiosperms, the gametophytes are extremely small and depend on the
much larger sporophyte for nutrition.
In addition, the gametophytes produce gametes in all groups of plants. In bryophytes and
seedless vascular plants, the sperm cells require water to swim to the egg. In
gymnosperms and angiosperms, the sperm nuclei are packaged into pollen, which is
carried to the plant by wind or animals and, therefore, does not require free water.
Answers to Pull It Together Questions
1. What are the main groups of plants within the bryophytes, seedless vascular plants,
gymnosperms, and angiosperms?
Bryophytes include mosses, liverworts and hornworts. Seedless vascular plants include
club mosses, whisk ferns, true ferns, and horsetails. Gymnosperms include conifers,
ginkgo trees, gnetophytes, and cycads. The two largest groups of angiosperms are
monocots and eudicots.
2. For each of the four main groups of plants, describe the gametophyte and sporophyte
generations.
Bryophytes
Seedless vascular plants
(e.g. ferns)
Gymnosperms
Angiosperms
Gametophyte
Supplies all nutrition for
plant; various shapes
Small, heart-shaped
Sporophyte
Various shapes; needs
gametophyte for nutrition
Large (fronds)
Microscopic; depends on
sporophyte for nutrition
Microscopic; depends on
sporophyte for nutrition
Large; makes cones
Large; makes flowers
3. How do bryophytes and seedless vascular plants reproduce if they lack pollen and
seeds?
Bryophytes and seedless vascular plants have gametophytes that produce gametes,
including swimming sperm. The sporophyte generation produces spores, which can be
dispersed to new habitats.
4. What is the relationship between pollen and seeds?
Pollen contains sperm nuclei that fertilize the egg and the polar nuclei. The fertilized
polar nuclei then develop into the endosperm, and the fertilized egg develops into an
embryo. The endosperm and embryo, surrounded by the seed coat, develop into the seed.