Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
21.1
1. How do stems, leaves, and roots support one another?
Stems hold leaves up to light, where they can photosynthesize and produce
carbohydrates. Sugars move via the stem from leaves to roots to nourish root cells. 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.
2. What are the other major parts of the plant body?
The shoot is the above ground portion of the plant. The node of a stem is a place where
leaves are attached. An internode is a length of stem located between nodes. The axillary
buds is an undeveloped shoot that can become a flower or a branch. The fruits carry the
seeds.
21.2
1. Which macro- and micronutrients do all plants require?
Macronutrients: carbon, oxygen, hydrogen, nitrogen, potassium, calcium, magnesium,
phosphorus, and sulfur. Micronutrients: chlorine, iron, boron, zinc, manganese, copper,
and molybdenum.
2. How do plants acquire C, H, O, N, and P?
C comes from CO2 absorbed from the atmosphere. H comes from water (H2O) absorbed
by the roots. O comes from H2O, CO2, or O2 in the atmosphere or dissolved in water. N
and P are dissolved in water absorbed by the roots.
3. How do bacteria form a critical link in the nitrogen cycle?
Nitrogen-fixing bacteria are responsible for fixing atmospheric nitrogen gas into
ammonium, a form that plants can take up in their roots.
21.3
1. Describe the cell types that make up a plant body.
 Parenchyma cells—the most numerous of cells, these cells are unspecialized with thin
walls and retain the ability to divide. These cells carry out major functions such as
photosynthesis, repair, and storage.
 Collenchyma cells—elongated cells with walls of various thickness providing elastic
support during growth.
 Sclerenchyma cells—thick walled cells of variable shape and length with lignin for
inelastic support.
 Tracheid cells—narrow, dead cells with overlapping walls that conduct water and
minerals through pits.
 Vessel elements—wide, dead cells arranged end to end that conduct water and
minerals through end walls.
 Sieve tube elements—living cells aligned end to end with sieve plates in the end walls
that conduct dissolved, organic materials.
 Companion cells—living cells connected to sieve tube elements by plasmodesmata,
which transfer material in and out of the sieve tubes.
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 dermal tissue and vascular tissue?
Dermal tissue secretes the cuticle, which retards loss of water from deeper plant tissues.
The functions of vascular tissues are to move water, minerals, carbohydrates, and other
dissolved substances within the plant.
21.4
1. Name the cell layers that occur 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. Compare and contrast the development of fibrous roots and taproots.
Both root types begin development with a primary root. At the tip is an apical meristem,
which is covered with a root cap that protects against abrasion. In both root systems, root
tips explore the soil seeking out water and minerals. In taproots, the primary root persists
through life, growing fast and deep and producing lateral branches. In fibrous root
systems, slender adventitious roots from the base of the stem replace the primary root,
producing a shallower root system.
5. How do the roots of monocots and eudicots differ?
Roots of monocots are fibrous, while eudicots usually have taproots. Internally, the roots
of eudicots have a central core of vascular tissue surrounded by a cortex and epidermis.
Monocot roots have a ring of vascular bundles surrounding a central pith. The ring is
surrounded by cortex and an epidermis.
21.5
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. Apical meristems allow roots
and shoots to grow in length. Lateral meristems are located in 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.
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 the secondary xylem to the inside, and secondary phloem to the
outside. The cork cambium produce parenchyma cells to the inside, and cork to the
outside.
4. 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
darker rings.
21.6
1. What are the components of xylem sap?
Xylem sap contains water and dissolved minerals.
2. How does transpiration occur?
Heat from the sun and from the plant’s metabolism causes water to evaporate into the
spaces between the mesophyll cells of a leaf. Water diffuses out of the leaf through open
stomata.
3. How do stomata help plants conserve water?
Guard cells close stomata when conditions are hot and dry, reducing the evaporation of
water from leaf tissues.
4. Summarize the cohesion–tension theory.
The cohesion-tension theory describes the movement of xylem sap, which results from
hydrogen bonds between water molecules. As water is lost in transpiration, water from
the leaf veins diffuses into the mesophyll. Water molecules leaving the vein “tug” on
adjacent water in the xylem sap. In this way, transpiration ultimately pulls water
molecules up the stem and, in turn, from soil into the roots.
5. What are the components of phloem sap?
Phloem sap is a solution containing organic compounds combined with water and
minerals from the xylem.
6. Explain the pressure flow theory of phloem transport.
The pressure flow theory states that phloem moves under positive pressure from sources
to sinks. A source is a structure that produces or releases sugars, and a sink is a plant part
that does not carry out photosynthesis.
7. What are some examples of sources and sinks in a plant?
Examples of sources are leaves, stems, or other green plant parts. Examples of sinks are
roots, fruits, shoot apical meristems, storage organs, flowers, or other plant parts that do
not carry out photosynthesis.
8. How does a parasitic plant infect a host?
After the seed of a parasitic plant germinates, the seedling secretes an adhesive material
that attaches the seedling to the host. As the seedling’s roots develop, they penetrate the
epidermis of the host, and absorb water and nutrients from the host’s vascular tissue.
21.7
1. Describe the hypothesis and experimental design in this study.
The scientists hypothesized that carnivorous plants face a tradeoff: the more leaf area
they devote to insect traps, the less leaf area available for photosynthesis. If nutrients are
abundant, the researchers, therefore, reasoned that the plants would construct smaller
traps and larger leaves. They tested their hypothesis by supplying different amounts of
nutrients to the plants and measuring the sizes of the pitchers and keels.
2. Predict how the graph in figure 21.23 would look if nitrogen did not affect pitcher
shape.
The keel size would not increase as nitrogen concentration increases, and the pitcher size
would remain similar to that of the control group.
Answers to Write It Out Questions
1. List the vegetative organs of a plant. How does each rely 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. Biologists often say that “form follows function”; that is, the form of a biological
structure facilitates its function. 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.
Organs
 Roots – anchoring; a network of roots holds the plant in the soil.
 Stems – support; tough fibers help keep a plant upright
 Leaves – photosynthesis; mesophyll cells possess chloroplasts
 Flowers – reproduction; the petals of many flower types attract pollinators
Tissues
 Ground tissue – storage; presence of plastids in some ground tissues
 Dermal tissue – protection; tough, waterproof periderm physically protects roots and
stems
 Vascular tissue – transportation; xylem and phloem are adjacent to each other,
allowing xylem to contribute water to phloem sap
Cell Types
 Parenchyma – storage; cells have vacuoles that store acids and other substances
 Collenchyma – support; thick, elastic cell walls
 Sclerenchyma – support; thick, tough cell walls
 Vessel elements and tracheids – transportation; cells lack cytoplasm that would
otherwise interfere with movement of water and nutrients
 Sieve tube elements – transportation; cells have sieve plates that allow the movement
of materials from cell to cell
3. How do plants obtain carbon and nitrogen?
A plant gets carbon by taking carbon dioxide in through the stomata. The plant obtains
nitrogen from the soil by absorbing it through the roots.
4. How might DNA technology (see chapter 11) be used to create transgenic plants that
can fix their own nitrogen? In what ways would this new feature change agriculture?
In theory, genes encoding enzymes required for nitrogen fixation could be moved from
nitrogen-fixing bacteria and inserted into the chromosomes of a plant. It would be
potentially valuable to agriculture because plants could fix their own atmospheric
nitrogen, which would reduce the need for nitrogen fertilizers.
5. Apoptosis (programmed cell death) is a normal part of development in both plants and
animals. Which plant tissues have cells that are dead at maturity? Why is it advantageous
to the plant for these cells to die?
Tracheids and vessel elements are also dead at maturity; as a result, cytoplasm does not
interfere with the flow of xylem sap. In addition, cork consists of layers of densely
packed, waxy cells that are dead at maturity. This is advantageous because the cells form
waterproof, insulating layers that protect the plant.
6. Corn is a monocot and sunflower is a eudicot. Make a chart that compares the stems,
leaves, and roots of these plants.
 Stems: Monocots have vascular bundles scattered throughout the ground tissue of the
stem; eudicots have a single ring of vascular bundles in the stem.
 Leaves: Monocot leaves have parallel veins; eudicot leaves have netted veins.
 Roots: Monocots have a ring of vascular bundles surrounding a central core (pith) of
parenchyma cells; eudicots have a vascular cylinder consisting of a solid core of
xylem, with phloem strands located between the “arms” of the xylem core.
7. Many biology labs use slides of root tips to demonstrate the stages of mitosis. Why is a
root tip a better choice than a mature leaf?
A root tip is the growing portion of the root which has the meristem. Mature leaves do
not contain meristematic tissue.
8. Thorns, spines, and tendrils are so highly modified that it can be difficult to tell
whether they derive from leaves or stems. How could a biologist use his or her
knowledge of plant anatomy to determine their origin?
The structures would have to be dissected for the examination of internal anatomy. A
leaf should have a network of veins and some mesophyll cells; a stem should have the
internal anatomy typical of a monocot or eudicot.
9. Describe why and how leaves and roots maximize surface area.
Most leaves have a broad, flat, thin blade that maximizes exposure to sunlight, which is
the plant’s energy source. Roots have numerous branches in the soil; in addition, root
hairs maximize the surface area to absorb water and minerals.
10. Mammals exchange gases in the alveoli of the lungs (see figure 27.17). How do the
structures and functions of leaf mesophyll compare with those of alveoli?
The mesophyll cells in the lower part of the leaf are separated by air spaces; when the
stomata are open, air can enter and gas exchange can occur across the cell membranes of
the mesophyll cells. Similarly, when the respiratory tract delivers air to the alveoli, gas
exchange can occur across the cell membranes of the alveoli and red blood cells.
11. Explain the evolutionary forces that selected for the cuticle, stomata, vascular tissue,
roots, stems, and leaves in land plants.
The cuticle decreases water loss; the stomata allow gas exchange in the presence of the
cuticle; vascular tissue provides support and a distribution system in large plants; roots
both anchor the plant and maximize the surface area for water and nutrient absorption;
stems support the leaves, providing an advantage in the competition for light; thin, broad
leaves maximize the surface area for photosynthesis.
12. Girdling is cutting away or severing the living bark in a ring around a tree’s trunk.
Which part of a girdled tree do you expect to die first, the roots or the shoot? Why?
Would the tree be harmed as much by a vertical gash? Why or why not?
The roots should die first, because living bark consists of the phloem that delivers sugars
to the belowground parts of the plant. A vertical gash would not be as harmful because
the phloem would remain intact.
13. Heartwood often contains chemicals that inhibit microbial growth. How are these
chemicals adaptive?
By inhibiting microbial growth in heartwood secondary xylem, the integrity of the stem is
maintained, so the stem doesn’t hollow out and collapse.
14. Make a chart comparing xylem and phloem transport. Include sap composition,
characteristics of the conducting cells, how the sap moves, whether the transport costs
energy, and direction of flow within the plant.
CHARACTERISTICS
Sap composition
XYLEM
Water and minerals
Conducting cells
Energy costs
Tracheids and vessels; dead
at maturity
Transpiration pulls water
from soil to roots to stems
None
Direction of flow
Roots to leaves
Sap movement
PHLOEM
Water, sugars, other organic
molecules
Sieve tube elements; alive at
maturity
Sap moves under pressure
from source to sink
Requires active transport to
load sugars into sieve tube
Sugar source to sink
15. Trace the path of water and dissolved minerals from soil, into the root’s xylem, and
up to the leaves.
Water enters the roots by osmosis; dissolved minerals enter root cells by passive or active
transport. After passing through the epidermis, the water and minerals may move
between or within cells of the cortex. Once the water and minerals encounter the
endodermis, a waxy strip forces water and minerals into cells. They, next, enter the
xylem, and are pulled up the stem and into leaves. Water vapor moves out of the stomata
as part of the transpiration stream.
16. Explain the role of cohesion in xylem transport.
As water molecules evaporate from the leaf, new molecules diffuse in from the vein.
Neighboring water molecules, attached by hydrogen bonds, are pulled up the stem and
into the vein. In turn, water is also pulled from roots into the stem, and from the soil into
the roots.
17. Review C3, C4, and CAM photosynthesis in chapter 5. Explain how plants that use
each pathway conserve water.
Like all land plants, C3 plants have a waxy cuticle and stomata that conserve water. C4
plants have smaller, fewer stomata than do C3 plants. CAM plants conserve water by
closing their stomata during the hot daylight hours.
18. Distinguish between a source and a sink. How can the same plant part act as both a
source and a sink?
A source is any plant part that produces or releases sugars; a sink is any plant part that
does not carry out photosynthesis. The same plant part can act as both a sink and a
source, because a sink may store carbohydrates that are later released to the rest of the
plant.
19. Peach and nectarine growers remove some flowers and small, immature fruits from
trees. Why does this practice yield larger, higher-quality fruit?
Removing some flowers and small fruits reduces the number of sinks, ensuring that the
remaining sinks will receive more sugar.
20. Suppose that a scientist exposes a leaf to CO2 labeled with carbon-14 and that the
radioactive carbon is incorporated into organic compounds in photosynthetic cells. At
various times after exposure, the scientist can determine the location of the radioactive
carbon in the plant. In what tissues do you expect to find the radioactive material
immediately after exposure to the labeled carbon? What about during transport? When
transport is complete, will the radioactive material be in plant parts above the leaf, below
the leaf, or both?
The radioactive 14C enters the leaf through stomata and is used immediately in
photosynthesis in a mesophyll cell. During transport, the 14C should be present in phloem
sap. The phloem may transport the sugar to any sink such as a flower, fruit, or root, and,
therefore, the 14C may end up either above or below the leaf.
21. Pitcher plants are threatened in the wild by habitat destruction and collection for plant
trade. Researchers are also concerned that air pollution will deposit additional nitrogen on
soil. How would additional nitrogen affect pitcher plants?
Additional nitrogen would result in a shift in leaf shape, selecting for a small diameter
pitcher and a larger keel (and eventually the loss of the pitcher). Continued added
nitrogen might change the selective pressures in the habitat, so that pitcher plants might
no longer be able to compete against other plant species.
22. Some architects specialize in building living roofs covered with plants. What are the
benefits and risks of living roofs? What raw materials must be supplied to plants living
on a roof? What types of plants would be the best choice? How does your answer depend
on where you live?
Benefits may include reduced CO2 and pollutant levels, insulation for the building, and
the provision of habitat for wildlife. Risks may include threats to the integrity of the roof
(e.g., increased weight or water damage) and the death of roof plants in extreme
conditions. Raw materials might include fertilizer, a way to capture and distribute water,
and a thin layer of soil. Plants should be evergreen and should have shallow roots,
relatively short stature, and the ability to withstand seasonal weather extremes.
Answers to Pull It Together Questions
1. Which nutrients come from soil? Which come from the atmosphere?
Roots absorb all mineral nutrients, including nitrogen, potassium, and phosphorus, from
soil. Oxygen and hydrogen also come from water absorbed from soil. Leaves absorb
carbon dioxide gas from the atmosphere.
2. How do parenchyma, collenchyma, and sclerenchyma fit into this concept map?
"Parenchyma" and "Collenchyma" connect with the phrase "are living cells found in" to
"Ground tissue". "Collenchyma" could also connect with the phrase "has thicker cell
walls than" to "Parenchyma". "Sclerenchyma" connects with the phrase "are cells that are
dead at maturity that are found in" to "Ground tissue".
3. What are the two types of meristems? How do they differ?
The two types of meristem are the apical meristem, which lengthens the stems and roots,
and the lateral meristem, which increases the girth of plants with secondary growth.
4. Add soil, source, sink, pressure flow, and transpiration to this map.
"Soil" connects with the phrase "is the source of" to "Mineral nutrients" and "Water".
"Phloem sap" connects with the phrase "moves by" to "Pressure flow", which connects
with the phrase "from" to "Source", and "Source" connects with the phrase "to" to "Sink".
"Transpiration" connects with the phrase "is the loss of water through open stomata in
the" to "Leaves".
5. What role do stomata play in transpiration?
Stomata are the openings through which water evaporates from the plant, pulling xylem
sap from the root to the shoot.