Download Answers to Mastering Concepts Questions

Mastering Concepts
22.1
1. How do stems, leaves, and roots support one another?
Stems hold leaves up to light, where they can produce carbohydrates by photosynthesis.
Sugars move via the stem from leaves to roots, flowers, fruits, and other
nonphotosynthetic plant parts. The roots anchor the plant and absorb water and minerals.
These substances move through the stem to the leaves, where they are used in
photosynthesis and other processes.
2. What is the relationship between the node and the internode of a stem?
The node of a stem is a place where leaves are attached. An internode is a length of stem
located between nodes.
3. Give examples of stems, leaves, and roots with specialized functions.
Specialized stems include tendrils (support of climbing stems), stolons and rhizomes
(horizontally oriented stems that produce new stems and roots), tubers (food storage),
succulent stems (water storage), and thorny stems (protection). Specialized leaves include
onion bulbs (food storage), cactus spines (protection), brightly colored leaves (pollinator
attraction), and carnivorous leaves (prey capture and digestion). Specialized roots include
beets and carrots (food storage), desert plant roots (water storage), aerial roots (gas
exchange or photosynthesis), and buttress or prop roots (support).
4. Categorize each structure in figure 22.1 as vegetative or reproductive.
The flowers and fruits are reproductive structures; all others are vegetative.
22.2
1. Compare and contrast tracheids, vessel elements, and sieve tube elements.
Tracheids, vessel elements, and sieve tube elements are similar in that they are cells that
transport materials within a plant. Tracheids and vessel elements are part of the xylem;
they transport water and dissolved minerals. Sieve tube elements are part of the phloem;
they transport sugars and other dissolved organic substances. Tracheids and vessel
elements are dead at functional maturity; sieve tube elements are alive at functional
maturity. Vessel elements lack end walls; tracheids have pits; and sieve tube elements
have sieve plates through which strands of cytoplasm pass from cell to cell.
2. Where in the plant does ground tissue occur?
Ground tissue fills the spaces between more specialized cell types inside stems, leaves,
fruits, and seeds. Most of the body of a plant is made of ground tissue.
3. What are the functions of vascular tissue?
The functions of vascular tissues are to move water, minerals, carbohydrates, and other
dissolved substances within the plant.
4. How does the structure of dermal tissue contribute to its functions?
Dermal tissue consists of a single layer of flat, transparent, tightly packed cells that cover
the leaf, stem, and roots of the plant. Dermal tissue secretes the cuticle, which retards
loss of water from deeper plant tissues. Stomata, which are surrounded by guard cells, are
pores that allow gases to move into and out of a leaf. When stomata are closed, they
prevent water loss from leaves.
22.3
1. Name the cell layers in the stem of a monocot and a eudicot, moving from the
epidermis to the innermost tissues.
Moving from the epidermis of a eudicot stem toward its center, the tissues are: epidermis;
cortex; vascular bundles composed of fibers, phloem, and xylem; and pith. Moving from
the epidermis of a monocot stem toward its center, the tissues are epidermis; vascular
bundles made of xylem, phloem, and fibers; and ground tissue. Vascular bundles are
arranged in a ring in a eudicot stem but scattered throughout a monocot stem.
2. List the parts of a simple and a compound leaf.
Both types of leaves have a blade, petiole, and axillary bud. Simple leaves have a single
blade while compound leaves have a divided blade.
3. Describe the internal anatomy of a leaf.
Inside a leaf, mesophyll cells are surrounded by air spaces that promote gas exchange as
the cells carry out photosynthesis. Veins contain xylem and phloem, which deliver water
and minerals and carry off sugars produced in photosynthesis. A waxy cuticle covers the
epidermis, and stomata are pores through which gases enter and leave the leaf.
4. Corn is a monocot and sunflower is a eudicot. Make a chart that compares the stems,
leaves, and roots of these plants.
Stem structure: Monocots have vascular bundles that are scattered throughout the ground
tissue of the stem; eudicots have a single ring of vascular bundles in the stem. Leaf
venation: Monocot leaves have parallel veins; eudicot leaves have netted veins. Root
organization: Monocots have a ring of vascular tissue surrounding a central core (pith) of
parenchyma cells; eudicots have a vascular cylinder consisting of a solid core of xylem,
with ridges that project into the pericycle. The phloem strands are generally located
between the “arms’ of the xylem core.
22.4
1. What is the difference between determinate and indeterminate growth?
A plant with determinate growth stops growing after it reaches its mature size. In
contrast, a plant with indeterminate growth can keep growing as long as the environment
can support it.
2. What are the locations and functions of meristems?
Apical meristems are located at the tips of roots and shoots; they allow these organs to
grow in length. Lateral meristems are form an internal cylinder of cells that extends along
most of the length of the plant. Lateral meristems allow an increase in girth of roots and
stems. Intercalary meristems occur in grasses and other monocots between the nodes of a
mature stem, often at the base of an internode. These meristems allow a plant to tolerate
repeated grazing and mowing because they regrow leaves from the base when the top of
the leaf is clipped off.
3. What are the two lateral meristems in a woody stem or root, and which tissues does
each meristem produce?
The two lateral meristems are the vascular cambium and the cork cambium. Vascular
cambium produces secondary xylem to the inside and secondary phloem to the outside.
The cork cambium produces parenchyma cells to the inside and cork to the outside.
4. What are the functions of wood and bark?
Wood, or secondary xylem, makes up most of the volume of a woody root or shoot.
Overall, wood is tough and provides support for the plant. In addition, the sapwood
conducts water and minerals, although the heartwood is nonfunctional. The main function
of bark is to protect the plant; in addition, secondary phloem in the bark conducts
carbohydrates within the plant.
5. How do softwoods differ from hardwoods?
Softwoods are composed mainly of tracheids, whereas hardwoods contain both tracheids
and vessels.
6. Explain the origin of tree rings.
Vascular cambium cells, dormant through the winter, divide and produce wood during
the spring and summer. During the wet spring months, the water conducting cells are
larger and the wood is lighter. During the drier summer, the cells are smaller and form
denser rings.
21.6
1. What is the overall question the researchers were asking in this study? Summarize the
data they used to arrive at their conclusion.
The overall question asked by the researchers was, “Why would natural selection select
for plants that expend energy on homes for ants (domatia), and do domatia increase the
reproductive success of the plant?” The data came from several related experiments.
The researchers used H. brunonis as a model organism because the same species provides
control groups without domatia and experimental groups with domatia. The researchers
used the number of fruits as a measure of reproductive fitness. Their first experiment
revealed that trees with domatia produce more fruit. Additional experiments revealed that
tramp ants, living in the domatia, quickly recognize herbivores and actively attack them,
thereby increasing the number of leaves available for photosynthesis. From these data the
researchers were able to conclude that the domatia indirectly improved reproductive
success in H. brunonis.
2. Propose an explanation for the observation that the trees secrete nectar only on young
leaves and not on tougher, more mature leaves.
Answers will vary, but one possible explanation is that herbivorous caterpillars prefer
young leaves. If so, then the plant would waste energy by attracting ants to mature leaves.
Write It Out
1. List the main vegetative organs of a plant, and explain how each relies on the others.
The vegetative (nonreproductive) organs of a typical plant include the roots, stems, and
leaves. The stem and leaves constitute the shoot. The stem supports the leaves, the main
sites of photosynthesis. The products of photosynthesis, in turn, nourish the nongreen
plant parts, including the roots. Most roots exist below ground, anchoring the plant and
absorbing water and minerals from the soil. These resources move via stems to the
leaves and other aboveground plant parts.
2. What selective pressures may have led to the thorny stems of cactus plants and the
aboveground roots of mangrove trees?
Cactus plants live in dry habitats, where water is scarce. Plants that can stockpile water
and defend it from thirsty animals should have greater reproductive success than those
that cannot. Mangrove trees grow in waterlogged soils, where oxygen is scarce. Roots
require oxygen to carry out their functions, so mangrove trees that can expose their roots
to the atmosphere should have greater reproductive success than those that cannot.
3. Imagine you are conducting an experiment on plant growth. You buy two seedlings,
plant them in identical soil, and water them the same amount each week. Each week you
also measure the plants’ heights. For the first two months, the plants grow at the same
rate. Then, one plant continues growing while the growth of the other plant slows and
eventually stops. Propose a possible cause for this observation.
One possibility is that the plant that kept growing was a variety with indeterminate
growth, whereas the other plant exhibited determinate growth.
4. Many biology labs use preserved slides of root tips to demonstrate the stages of
mitosis. Why is this a better choice than using a slide of a mature leaf?
The tips of roots consist of rapidly dividing meristematic cells that show all the stages of
mitosis; the leaf does not contain meristematic tissue.
5. Write nonbiological analogies for vessel elements, phloem, stomata, and lignin.
Many answers are possible; these are examples. Vessel elements are like Lifesavers
candies stacked on top of one another. Phloem is like a conveyer belt that delivers
baggage (carbohydrates) from an airplane (leaf) to the baggage claim (root or other
“sink”). Stomata are like a home’s doors, which can open or close according to the
occupants’ needs. Lignin adds strength to xylem cell walls, like the metal bars in
reinforced concrete.
6. Predict why it might be more adaptive for a tree to produce thousands of small leaves
rather than one huge leaf.
One possible explanation is that multiple small leaves are more versatile than one large
one. For example, branches can produce new leaves where the light is brightest and
invest less energy in leaves in shaded areas. In addition, if a plant’s single huge leaf is cut
off or damaged, the plant has no “backup” leaves to carry out photosynthesis.
7. Search the Internet for an angiosperm evolutionary tree. Analyze the tree and then use
the principles of shared ancestry to explain why monocots have embryos with one
cotyledon, eudicots have embryos with two cotyledons, and both have seeds contained
within fruits.
Monocots, eudicots, and all other angiosperms share a common ancestor that had seeds
and fruits. The descendants of that common ancestor branched into multiple groups, some
of which had one cotyledon and gave rise to the common ancestor of all monocots, and
some of which had two cotyledons and gave rise to the common ancestor of all eudicots.
8. List the structures that help a plant maintain water homeostasis.
Structures that help a plant maintain water homeostasis include the stomata, cuticle,
xylem, endodermis, and root hairs.
9. Explain how conditions in the terrestrial environment selected for each of the
following adaptations: cuticle, stomata, vascular tissue, roots, stems, and leaves.
Water evaporates quickly from a land plant’s tissues; the cuticle decreases water loss, and
the stomata allow gas exchange in the presence of the cuticle. Air provides little physical
support; vascular tissue provides not only support but also a transportation system in
large plants. On land, water and minerals are in soil whereas CO2 and sunlight are
aboveground. This division of resources selects for a division of labor in a plant: the roots
both anchor the plant and maximize the surface area for water and nutrient absorption,
whereas stems support the leaves. The leaves, in turn, maximize the surface area for
photosynthesis.
10. Consider the picture in the Burning Questions box on page 464. Which of the plant
parts shown in the picture fit the biological definition of a fruit?
The cucumber and bell peppers are fruits.
11. The Cork Forest Conservation Alliance is a nonprofit environmental organization
dedicated to preserving the cork forests of the Mediterranean. Visit their website and then
explain to a friend why buying wine closed with natural cork is more environmentally
friendly than buying wine closed with a screw cap.
One argument that natural cork is more environmentally friendly than a metal screw cap
is that cork is a renewable resource, whereas metal is nonrenewable.
12. Suppose you drive a metal spike from the outermost bark layer to the center of a
tree’s trunk. Which tissues does your spike encounter as it moves through the stem, and
what type of meristem produced each type?
The spike will strike the cork and a thin layer of parenchyma, both produced by the cork
cambium. It will then strike the secondary phloem and enter the secondary xylem, both
produced by the vascular cambium.
13. List a function of each organ, tissue, and cell type described in this chapter, and then
list at least one feature that facilitates that function.
Vegetative organs include stems, leaves, and roots. Stems provide support; tough fibers
help keep a plant upright. Leaves carry out photosynthesis; mesophyll cells contain
chloroplasts with photosynthetic pigments. Roots absorb water and minerals; root hairs
boost the surface area for absorption.
Tissues include ground tissue, dermal tissue, and vascular tissue. Ground tissue provides
storage; some tissues are rich in starch-storing plastids. Dermal tissue protects a plant; a
tough, waterproof periderm physically protects woody roots and stems. Vascular tissue
transports materials; xylem and phloem are adjacent to each other, allowing xylem to
contribute water to phloem sap
Cell types include parenchyma, collenchyma, sclerenchyma, vessel elements and
tracheids, and sieve tube elements. Parenchyma cells provide storage; these cells contain
vacuoles that store acids and other substances. Collenchyma cells provide support; these
cells have thick, elastic cell walls. Sclerenchyma cells also provide support; they have
thick, tough cell walls strengthened with lignin. Vessel elements and tracheids transport
water within a plant; these cells lack cytoplasm that would otherwise interfere with water
movement. Sieve tube elements transport dissolved organic substances; these cells have
sieve plates that allow the movement of materials from cell to cell.
Pull It Together
1. Add the terms cortex, pith, mesophyll, endodermis, and Casparian strip to this concept
map.
“Ground tissue” connects with the phrase “filling the interior of a stem or root is” to
“pith” and “cortex.” “Ground tissue” connects with the phrase “inside a leaf is” to
“mesophyll.” “Casparian strip” connects with the phrase “is a waxy coating on the” to
“endodermis,” which connects with the phrase “is a layer of cells inside a” to “root.”
2. Connect monocots and eudicots to vascular tissue. Your connecting phrases should
indicate a difference between the two plant groups.
“Monocots” connects with the phrase “have stems with scattered bundles of” to “vascular
tissue.” “Eudicots” connects with the phrase “have stems containing a ring of bundles of”
to “vascular tissue.”