46) The enzyme complex nitrogenase catalyzes the reaction that reduces atmospheric nitrogen to
A) N2.
B) NH3.
C) NO2.
D) NO+.
E) NO–.
47) In a root nodule, the gene coding for nitrogenase
A) is inactivated by leghemoglobin.
B) is absent in active bacteroids.
C) is found in the cells of the pericycle.
D) protects the nodule from nitrogen.
E) is part of the Rhizobium genome.
48) The most efficient way to increase essential amino acids in crop plants for human consumption
would be to
A) breed for higher yield of deficient amino acids.
B) increase the amount of fertilizer used on fields.
C) use 20-20-20 fertilizer instead of 20-5-5 fertilizer.
D) engineer nitrogen-fixing nodules into crop plants lacking them.
E) increase irrigation of nitrogen-fixing crops.
49) Which of the following habitats would most likely have a high proportion of species of plants that
are in symbiotic association with nitrogen-fixing bacteria?
A) anoxic soils such as fens and bogs
B) nutrient-limiting soils such as wet tropical rain forests
C) loamy soils such as temperate forests
D) agriculturally productive regions that have gone fallow
E) alpine coniferous forests
50) If a plant is infected with nitrogen-fixing bacteria, what is the most probable effect on the plant?
A) It gets chlorosis.
B) It dies.
C) It is supplied with increased essential elements from the soil.
D) It will likely grow faster.
E) It becomes flaccid due to the loss of water and nutrients from the roots.
51) You are weeding your garden when you accidentally expose some roots of your pea plants. You
notice swellings (root nodules) on the roots and there is a reddish tinge to the ones you accidentally
damaged. Most likely your peas plants
A) suffer from a mineral deficiency.
B) are infected with a parasite.
C) are benefiting from a mutualistic bacterium.
D) are developing offshoots from the root.
E) contain developing insect pupa.
52) Which of the following is a true statement about nitrogen fixation in root nodules?
A) The plant contributes the nitrogenase enzyme.
B) The process is relatively inexpensive in terms of ATP costs.
C) Leghemoglobin helps maintain a low O2 concentration within the nodule.
D) The process tends to deplete nitrogen compounds in the soil.
E) The bacteria of the nodule are autotrophic.
53) Upregulation of leghemoglobin biosynthesis in a leguminous species would most likely indicate
A) the plant is suffering from a mineral deficiency.
B) the successful inoculation of nitrogen-fixing bacteria.
C) the plant is suffering from water stress.
D) the plant has been infected with mycorrhizae.
E) an increase in the biosynthesis of amino acids.
54) Which of the following is not a function of rhizobacteria?
A) produce hormones that stimulate plant growth
B) produce antibiotics that protect roots from disease
C) absorb toxic metals
D) carry out nitrogen fixation
E) supply growing roots with glucose
55) A woodlot was sprayed with a fungicide. What would be the most serious effect of such spraying?
A) a decrease in food for animals that eat mushrooms
B) an increase in rates of wood decay
C) a decrease in tree growth due to the death of mycorrhizae
D) an increase in the number of decomposing bacteria
E) a decrease in food for animals that eat mushrooms, and an increase in rates of wood decay
56) An example of a mutualistic association between a plant and a fungus would be
A) nitrogen fixation.
B) Rhizobium infection.
C) mycorrhizae.
D) parasitic infection.
E) assisted pollination.
57) Hyphae form a covering over roots. These hyphae create a large surface area that helps to do which
of the following?
A) aid in absorbing minerals and ions
B) maintain cell shape
C) increase cellular respiration
D) anchor a plant
E) protect the roots from ultraviolet light
58) Which of the following is a primary difference between ectomycorrhizae and endomycorrhizae?
A) Endomycorrhizae have thicker, shorter hyphae than ectomycorrhizae.
B) Endomycorrhizae, but not ectomycorrhizae, form a dense sheath over the surface of the root.
C) Ectomycorrhizae do not penetrate root cells, whereas endomycorrhizae grow into invaginations of the
root cell membranes.
D) Ectomycorrhizae are found in woody plant species; about 85% of plant families form
ectomycorrhizae.
E) There are no significant differences between ectomycorrhizae and endomycorrhizae.
59) The earliest vascular plants on land had underground stems (rhizomes) but no roots. Water and
mineral nutrients were most likely obtained by
A) absorption by hairs and trichomes.
B) diffusion through stomata.
C) absorption by mycorrhizae.
D) osmosis through the root hairs.
E) diffusion across the cuticle of the rhizome.
60) Dwarf mistletoe grows on many pine trees in the Rockies. Although the mistletoe is green, it is
probably not sufficiently active in photosynthesis to produce all the sugar it needs. The mistletoe also
produces haustoria. Thus, dwarf mistletoe growing on pine trees is best classified as
A) an epiphyte.
B) a nitrogen-fixing plant.
C) a carnivorous plant.
D) a symbiotic plant.
E) a parasite.
61) What are epiphytes?
A) aerial vines common in tropical regions
B) haustoria used for anchoring to host plants and obtaining xylem sap
C) plants that live in poor soil and digest insects to obtain nitrogen
D) plants that grow on other plants but do not obtain nutrients from their hosts
E) plants that have a symbiotic relationship with fungi
62) Carnivorous plants have evolved mechanisms that trap and digest small animals. The products of
this digestion are used to supplement the plant’s supply of
A) energy.
B) carbohydrates.
C) lipids and steroids.
D) minerals.
E) water.
63) Plant roots can enhance the availability of mineral nutrients for uptake by
A) increased respiration.
B) increased photosynthesis.
C) release of chelating agents.
D) growing faster.
E) acidifying the soil.
64) Rhizobia and mycorrhizae share all of the following features except
A) they both benefit by receiving carbohydrate from the plant.
B) many are host-specific.
C) they both become parasitic in nutrient-rich environments.
D) they both enhance the growth of most plants.
E) they both are found in most ecosystems of the world.
65) Rhizobia, actinomycetes, and cyanobacteria all share the common feature that they can
A) increase water uptake in plants.
B) increase nutrient availability in the soil for plants.
C) kill parasites in the soil.
D) exist in extreme environments.
E) fix atmospheric nitrogen.
66) Which soil type or habitat would be least likely to have high populations of mycorrhizae?
A) acidic bogs and fens
B) loamy soils
C) sandy soils
D) tropical forests
E) desert soils
Art Questions
Figure 37.1 shows the results of a study to determine the effect of soil air spaces on plant growth.
Figure 37.1
67) The best conclusion drawn from the data in Figure 37.1 is that the plant
A) grows best without air in the soil.
B) grows fastest in 5-10% air.
C) grows best at soil air levels above 15%.
D) does not respond differently to different levels of air in the soil.
E) would grow to 24 grams in 40% soil air.
68) The data in Figure 37.1 indicate that the plant
A) grows best at the lower levels of air in the soil.
B) grows about the same in 15% and 20% soil air levels.
C) grows best in soil air levels above 15%.
D) grows about the same in 15% and 20% soil air levels, and grows best in soil air levels above 15%.
E) grows about the same in 15% and 20% soil air levels, grows best in soil air levels above 15%, and
grows best at the lower levels of air in the soil.
69) The best explanation for the shape of the growth response curve in Figure 37.1 is that
A) the plant requires air in the soil for photosynthesis.
B) the roots are able to absorb more nitrogen (N2) in high levels of air.
C) most of the decrease in weight at low air levels is due to transpiration from the leaves.
D) increased soil air produces more root mass in the soil but does not affect the top stems and leaves.
E) the roots require oxygen for respiration and growth.
In west Texas, cotton has become an important crop in the last several decades. However, in this hot, dry
part of the country there is little rainfall, so farmers irrigate their cotton fields. They must also regularly
fertilize the cotton fields because the soil is very sandy. Figure 37.2 shows the record of annual
productivity (measured in kilograms of cotton per hectare of land) since 1960 in a west Texas cotton
field. Use these data to answer the following questions.
Figure 37.2
70) Based on the information provided in Figure 37.2, what is the most likely cause of the decline in
productivity?
A) The farmer used the wrong kind of fertilizer.
B) The cotton is developing a resistance to the fertilizer and to irrigation water.
C) Water has accumulated in the soil due to irrigation.
D) The soil water potential has become more negative due to salination.
E) The rate of photosynthesis has declined due to irrigation.
71) If you were the county agriculture agent, what would be the best advice you could give the farmer
who owns the field under study in Figure 37.2?
A) Plant a variety of cotton that requires less water and can tolerate salinity.
B) Continue to fertilize, but stop irrigating the field and rely on rainfall.
C) Continue to irrigate, but stop fertilizing the field and rely on organic nutrients in the soil.
D) Continue to fertilize and irrigate, but add the nitrogen-fixing bacteria Rhizobium to the irrigation
water until the productivity increases.
E) Add acid to the soil and increase its cation exchange capabilities so more nutrients are retained in the
soil.
Scenario Questions
72) You are conducting an experiment on plant growth. You take a plant fresh from the soil that weighs
5 kg. Then you dry the plant overnight and determine the dry weight to be 1 kg. Of this dry weight, how
much would you expect to be made up of organic molecules?
A) 1 gram
B) 4 grams
C) 40 grams
D) 960 grams
E) 1 kg
73) A group of 10 tomato plants are germinated and maintained in a large tray with no drainage. After
several weeks they all begin to wilt and die despite repeated watering and fertilization. The most likely
cause of this die-off is
A) competition for resources.
B) anoxia.
C) organic nutrient depletion.
D) no room left for root growth.
E) buildup of toxic substances in the tray.
74) A greenhouse experiment to test growth rates in tomato cultivars was conducted using sterile soil
mix and watering with sterile solutions of water and fertilizer. Following germination, half of the plants
in each group were transplanted into soil that was obtained from a nearby agricultural field (nonsterile),
the other half into sterile soil. After several weeks the plants that were transplanted into nonsterile soil
exhibited a much higher growth rate compared to the plants transplanted into sterile soil. The most likely
explanation for this result is
A) the plants transplanted into the nonsterile soil were inoculated with mycorrhizae.
B) the plants transplanted into the nonsterile soil received more fertilizer.
C) the plants transplanted into the sterile soil were stunted due to overfertilization.
D) the plants transplanted into sterile soil suffered anoxia from improper water drainage.
End-of-Chapter Questions
The following questions are from the end-of–chapter “Test Your Understanding” section in Chapter 37
of the textbook.
75) Most of the mass of organic material of a plant comes from
A) water.
B) carbon dioxide.
C) soil minerals.
D) atmospheric oxygen.
E) nitrogen.
76) Micronutrients are needed in very small amounts because
A) most of them are mobile in the plant.
B) most serve mainly as cofactors of enzymes.
C) most are supplied in large enough quantities in seeds.
D) they play only a minor role in the growth and health of the plant.
E) only the most actively growing regions of the plants require micronutrients.
77) Mycorrhizae enhance plant nutrition mainly by
A) absorbing water and minerals through the fungal hyphae.
B) providing sugar to root cells, which have no chloroplasts.
C) converting atmospheric nitrogen to ammonia.
D) enabling the roots to parasitize neighboring plants.
E) stimulating the development of root hairs.
78) Epiphytes are
A) fungi that attack plants.
B) fungi that form mutualistic associations with roots.
C) nonphotosynthetic parasitic plants.
D) plants that capture insects.
E) plants that grow on other plants.
79) Some of the problems associated with intensive irrigation include all but
A) mineral runoff.
B) overfertilization.
C) land subsidence.
D) aquifer depletion.
E) soil salinization.
80) A mineral deficiency is likely to affect older leaves more than younger leaves if
A) the mineral is a micronutrient.
B) the mineral is very mobile within the plant.
C) the mineral is required for chlorophyll synthesis.
D) the mineral is a macronutrient.
E) the older leaves are in direct sunlight.
81) We would expect the greatest difference in plant health between two groups of plants of the same
species, one group with mycorrhizae and one group without mycorrhizae, in an environment
A) where nitrogen-fixing bacteria are abundant.
B) that has soil with poor drainage.
C) that has hot summers and cold winters.
D) in which the soil is relatively deficient in mineral nutrients.
E) that is near a body of water, such as a pond or river.
82) Two groups of tomatoes were grown under laboratory conditions, one with humus added to the soil
and one a control without humus. The leaves of the plants grown without humus were yellowish (less
green) compared with those of the plants grown in humus-enriched soil. The best explanation for this
difference is that
A) the healthy plants used the food in the decomposing leaves of the humus for energy to make
chlorophyll.
B) the humus made the soil more loosely packed, so water penetrated more easily to the roots.
C) the humus contained minerals such as magnesium and iron, needed for the synthesis of chlorophyll.
D) the heat released by the decomposing leaves of the humus caused more rapid growth and chlorophyll
synthesis.
E) the healthy plants absorbed chlorophyll from the humus.
83) The specific relationship between a legume and its mutualistic Rhizobium strain probably depends
on
A) each legume having a chemical dialogue with a fungus.
B) each Rhizobium strain having a form of nitrogenase that works only in the appropriate legume host.
C) each legume being found where the soil has only the Rhizobium specific to that legume.
D) specific recognition between the chemical signals and signal receptors of the Rhizobium strain and
legume species.
E) destruction of all incompatible Rhizobium strains by enzymes secreted from the legume’s roots.