Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 20
20.1
1. 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. 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. Alternation of generations in plants is a life cycle in which a multicellular diploid (sporophyte)
stage alternates with a multicellular haploid (gametophyte) stage.
4. Some adaptations that enable plants to thrive on land include the cuticle, stomata, lignin, and
vascular tissue.
5. 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.
6. The presence or absence of swimming sperm, vascular tissue, pollen, seeds, flowers, and
fruits differentiate the four major groups of plants.
20.2
1. Mosses are small bryophytes with compact bodies and structures resembling stems and
leaves. Liverworts have flattened, lobed bodies that lack stems. Hornworts have tapering pointed
sporophytes and flat gametophytes.
2. Bryophytes reproduce asexually by forming gemmae, small pieces of tissue that detach and
grow into new plants. 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.
3. Mosses occur more frequently in moist, shady habitats because they must be covered by a film
of water for sexual reproduction to occur.
20.3
1. Vascular tissue allows plants to transport water and nutrients internally, which helps them to
survive in dry locations. Vascular tissue also provides strength, which allows vascular plants to
grow larger than bryophytes.
2. The four groups of seedless vascular plants are:
- true ferns, which have fronds that grow from rhizomes and spores on the undersides of the
fronds;
- club mosses, which have reproductive structures that look like clubs or spikes;
- horsetails, which have branched rhizomes and stems that bear spores at their tips;
- whisk ferns, which have rhizomes but lack roots and leaves. They look like whisk brooms.
3. 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.
4. Seedless vascular plants are similar to and different from bryophytes because both are tied to
water by their swimming sperm that require water to reach eggs. Neither group has pollen, seeds,
flowers, or fruits.
20.4
1. Seeds and pollen enable plants to live and reproduce in dry climates because pollen does not
require environmental water to reach female tissues that contain eggs. Seeds contain
nourishment for the dormant plant embryo and may remain viable for extremely long periods of
time, germinating when conditions are right.
2. The characteristics of gymnosperms include vascular tissue, pollen, and naked seeds that are
not enclosed in fruits.
3. The four groups of gymnosperms are conifers, cycads, ginkgos, and gnetophytes.
4. Meiosis, pollination, and fertilization occur inside the cone. The gametophyte generation is also
produced within cones.
5. 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 cell unites with the haploid egg cell, producing a zygote that will grow
into the sporophyte generation.
20.5
1. Angiosperms are similar to gymnosperms in that they are vascular plants that have pollen and
seeds. Angiosperms are different from gymnosperms in that they produce flowers, which in turn
produce the pollen and eggs. After fertilization (which occurs within the flower), the flower parts
develop into a fruit that encloses the seeds.
2. Monocots have one cotyledon, whereas dicots have two cotyledons.
3. Angiosperms and their pollinators illustrate coevolution because flowers often have shapes that
fit the animals that pollinate them. The flowers usually offer their pollinators food rewards, and the
pollinators ensure that flowers receive pollen of the correct species.