CHAPTER 32 Test Your Knowledge
DRIVING QUESTION 1
How is a plant body structured, and how do plants obtain water and grow?
By answering the questions below and studying Infographics 32.1 and 32.2, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Draw and label a diagram of two adjacent plant cells. Include key intracellular structures.
See Infographic 32.1.
Which of the following statements represents a true distinction between xylem and phloem?
a. Xylem provides support only; phloem provides transport.
b. Xylem provides water and nutrient transport; phloem provides sugar transport.
c. Xylem transports materials from shoots to roots; phloem transports materials in either direction.
d. Xylem transports sugars in either direction; phloem transports water from roots to shoots
e. all of the above
b
What is the function of the cuticle?
a. It enables neighboring cells to stick together.
b. It provides rigidity to the cell wall.
c. It is toxic to many herbivorous insects.
d. It prevents water loss.
e. It is sticky and helps pollen stick to a plant during pollination.
d
USE IT
Paper is made from wood that is broken down to pulp. Why are lignin-digesting enzymes included in the pulping process? Would these enzymes have to be included in the pulping process if paper were made from green leaves? Explain your answer.
Wood contains lignin in its cell walls. Lignin-digesting enzymes are necessary to break down this very hard and durable substance. If paper were made from green leaves, lignin-digesting enzymes would not be necessary, as the cells of green leaves do not have lignin in their cell walls.
DRIVING QUESTION 2
How do plants obtain nutrients?
By answering the questions below and studying Infographics 32.3, 32.4, and 32.5, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Plants are autotrophs and can make sugar from CO2. How do they obtain CO2?
a. through stomata
b. by absorption through the root system
c. by digesting insects
d. by breaking down carbon-rich carbohydrates stored in roots
e. a and b
a
When stomata are open, what is happening?
a. O2 is entering the plant for photosynthesis.
b. CO2 is entering the plant for photosynthesis.
c. H2O is entering the plant for photosynthesis.
d. H2O is leaving the plant.
e. a, b, and c
f. b and d
f
What is found in root nodules?
a. PEP carboxylase
b. CO2
c. bacteria
d. phosphorus
e. stored glucose
c
USE IT
Describe the “conflict” that plants face with respect to opening and closing their stomata.
Plants must open their stomata to let in CO2 for photosynthesis. Most plants open their stomata during the day (when photosynthesis is occurring). However, when the stomata are open, water is lost by evaporation. In dry climates, the water loss can be severe and detrimental. This creates the “conflict” between the need to let in carbon dioxide and the need to minimize water loss through open stomata.
Are trumpet pitchers strict autotrophs? Explain your answer.
No. Trumpet pitchers supplement their nutrition by digesting other organisms—insects.
If you applied to the soil around your plants a chemical that kills bacteria (but not plants), why might your plants die?
You might have killed the nitrogen-fixing bacteria in the soil, reducing the amount of usable nitrogen available to the plant.
Why may the bright coloration of a trumpet pitcher have a different function than do the bright colors of yellow or orange squash blossoms? (Hint: Squash are pollinated by bees.)
The bright coloration of the trumpet pitcher attracts insects, a food source that can supplement their nutrition. The bright coloration of the squash blossoms attracts pollinating insects that will transfer pollen from one squash blossom flower to the next.
If a plant could not make chlorophyll, would you expect it to survive? Why or why not?
It would not survive. Chlorophyll is critical for photosynthesis, and without chlorophyll the plant would not be able to carry out photosynthesis and make its own food.
INTERPRETING DATA
Scientists carried out an experiment to examine the effect of CO2 concentrations on plant growth in a semi-arid (that is, a dry) grassland environment in Colorado. They set up several plots in the field, consisting of chambers that allowed the concentration of CO2 to be controlled. One set of plots (A) was kept at ambient CO2 concentration, and one set (B) was kept at elevated CO2 concentration (two times ambient). In mid-July the total plant mass in each plot set was recorded. The data for three consecutive years are shown in the table. (In order to establish a baseline, the CO2 levels in 1996 were not manipulated.)
a. Graph these data.
b. Are there any differences between different plot sets in any given year? If so, describe the differences observed.
c. Are there any differences in the same plot set between years? If so, describe the differences and propose an explanation.
d. What are the implications of this study for grassland productivity (at least in Colorado) with rising CO2 levels?
a: Graph is not included in answer key. b: In 1997 and 1998, plot B (elevated CO2) had higher plant mass than plot A. This is presumably because of the elevated amounts of CO2 applied to plot B in 1997 and 1998. c: Plot A had higher amounts of plant mass in 1998 relative to 1996 and 1997. Plot B had more plant mass in 1997 (relative to baseline in 1996), and still more in 1998. Both plots A and B had higher amounts of plant mass in 1998 compared to 1997. This may have been because of environmental factors such as rainfall (if 1997 was particularly dry and 1998 was wetter) or temperature. d: The data suggest that CO2 enhances grassland plant growth. This suggests that these regions should continue to grow well as CO2 levels rise, as long as temperature and rainfall are at levels that permit grasslands growth.
SOURCE: Morgan, J. A., et al. (2001) Elevated CO2 enhances water relations and productivity and affects gas exchange in C3 and C4 grasses of the Colorado shortgrass steppe. Global Change Biology 7:451–466.
DRIVING QUESTION 3
How do plants reproduce, respond to stimuli, and protect themselves?
By answering the questions below and studying Infographics 32.6, 32.7, 32.8, 32.8, 32.10, and 32.11, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
What characterizes a dormant seed?
a. the presence of sperm
b. the presence of eggs
c. the presence of an embryonic plant
d. the absence of ABA
e. the presence of several pollen grains
c
Describe how fertilization follows pollination in an angiosperm. What has to happen, and what plant structures are involved?
The pollen grain lands on the stigma (pollination). The pollen grain produces a tube that grows down the style. The sperm from the pollen grain travel in this tube to the ovule, where an egg is fertilized.
Which of the following pigments are present in green leaves late in the summer?
a. chlorophyll
b. carotene
c. xanthophyll
d. all of the above
e. a and b
d
Which of the following hormones helps fruit to ripen?
a. auxin
b. ethylene
c. gibberellins
d. estrogen
e. anthocyanin
b
If you wanted a plant to grow really tall, which hormone should you apply?
a. auxin
b. ethylene
c. gibberellins
d. anthocyanin
e. ABA
c
USE IT
Why do seedless grapes need hormone treatment to develop big clusters of big grapes, while seeded varieties can develop large fruits without exogenous (that is, externally applied) hormones?
Gibberellins are responsible for the elongation of stems that allow large bunches of grapes. Gibberellins are naturally produced by the seeds. Seedless varieties therefore do not produce gibberellins and so must be treated with exogenous hormones.
Nopales are cactus pads (the large, thick “leaves” of the prickly pear cactus) and make a delicious salad. What antiherbivory mechanism fails when we succeed in making ensalada de nopales—prickly pear salad?
The prickly spines on the prickly pear cactus protect the plant from herbivores. By removing the spines for the salad, humans are circumventing this antiherbivory mechanism.
MINI CASE
The Natural Products Branch of the National Cancer Institute looks for defensive compounds produced by plants, microbes, and marine organisms that may have anticancer activity. Once compounds have been isolated, they can be chemically modified to enhance their activity. Several drugs have come out of this program, including eribulin mesylate, a chemically modified compound originally purified from a sea sponge. This drug has been approved for women with metastatic breast cancer whose disease thus far has not been responsive to treatment. In a clinical trial, patients taking eribulin mesylate had a significantly longer survival time (13.1 months) than patients taking chemotherapy regimens prescribed by their oncologists (10.6 months). (Data are from http://www.cancer.gov/ncicancerbulletin/041911/page5.)
The first step in developing drugs such as these is to prepare extracts by grinding up the natural product. Design a procedure to test such extracts for anticancer activity. Consider what tests you will use to determine if an extract has an anticancer activity, and what variables you will measure and manipulate in order to find promising candidates to advance along the drug discovery pipeline.
Extracts must be tested for anticancer activity, but they cannot be immediately tested in humans. One assay for anticancer activity is to apply different concentrations of the extract to human cancer cells grown in laboratory dishes. A variety of cancer cell lines exist from different types of cancer—lung, breast, cervical, and others. Once the extract has been applied to cells, you could measure their growth rate (relative to control cancer cells with no extract applied), or look for cell death. A promising extract would slow the growth of cancer cells or kill them. It would also be important to test the extract on normal (noncancer) human cells to make sure that it is not equally detrimental to normal cells. Once an extract has been identified as having potential anticancer activity in cultured human cancer cells, it is important to identify the specific compounds in the extract that are responsible for the growth slowing/killing effects. The crude extract could be chemically separated into its individual chemical components, and each of these could be tested against the panel of cancer and normal cell lines to see if a single compound has the same effect as the crude extract. If such a chemical compound is identified, it can then be subjected to chemical modification in the lab, to see if it possible to enhance its activity. It can also be tested in an animal model of cancer to establish safety and possible in vivo anticancer activity before any testing in humans.
BRING IT HOME
Many everyday products contain compounds derived from plants. A few of these are: Caffeinated sodas or energy drinks
Camphor and menthol-containing vapor rubs and steams (for congestion and muscle aches) Nicotine
Tea tree oil for minor skin irritations and infections
Quinine-containing tonic water
You, members of your family, or your friends may have used some or all of these. For each item listed, do some internet research to identify the plant (find both the scientific and common name) and something else about it that interests you (e.g., where is the plant found, whether it has historically been used for medicinal purposes, are there other sources of the compound).
Caffeine: Camellia sinensis (tea plant); Coffea arabica (coffee plant)
Camphor: Cinnamomum camphora (camphor tree)
Menthol: Mentha species (mint plants)
Nicotine: Nicotiana tabacum (cultivated tobacco)
Tea Tree Oil: Melaleuca alternifolia (Australian tea tree)
Quinine in tonic water: Cinchona ledgeriana (cinchona tree)
Further answers will vary.