Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 37
Test Yourself Questions
1. Which of the following substances can limit plant growth in nature?
a. sunlight
b. water
c. carbon dioxide
d. fixed nitrogen
e. all of the above
Answer: e. Sunlight, water, carbon dioxide, fixed nitrogen, and other nutrients can limit plant growth if
present in insufficient amounts.
2. In what form do plants take up most soil minerals?
a. as ions dissolved in water
b. as neutral salts
c. as mineral-clay complexes
d. linked to humus particles
e. none of the above
Answer: a. Plants take up most soil minerals as ions dissolved in water.
3. Why do plants need sulfur?
a. in the construction of cell walls
b. as an essential component of chlorophyll
c. to produce the amino acids cysteine and methionine
d. all of the above
e. none of the above
Answer: c. Plants need sulfur to produce cysteine and methionine, and some plants use sulfur to
produce defense compounds.
4. Humus is:
a. a food produced from garbanzo beans
b. the organic constituents of soils
c. the inorganic constituents of soils
d. the bedrock layer of soils
e. none of the above
Answer: b. Humus is the organic constituents of soils, and is largely derived from the partially
decomposed remains of plants.
5. Which environments are most conducive to heavy leaching of minerals from soils?
a. those having soils that are composed primarily of sand particles
b. those having acidic soils
c. those impacted by acid rain
d. regions characterized by heavy rainfall
e. all of the above
Answer: e. Sandy soils, acidic soils, acid rain, and heavy rainfall all foster leaching of minerals from
soils, thereby decreasing fertility.
6. Which property is not characteristic of clay-rich soils?
a. high mineral nutrient retention
b. high water retention
c. aeration
d. lower amounts of sand than clay
e. all of the above
Answer: c. Clay-rich soils lack aeration, for which reason gardeners often mix organic materials and
sand into them.
7. Which of the substances listed below is toxic to plants?
a. carbon dioxide
b. oxygen
c. atmospheric nitrogen gas
d. aluminum
e. none of the above
Answer: d. Aluminum is a very common constituent of soils and is toxic to plants.
8. What kinds of organisms occur in nitrogen-fixing symbioses with plants?
a. cyanobacteria
b. actinobacteria
c. rhizobia bacteria
d. all of the above
e. none of the above
Answer: d. Cyanobacteria, actinobacteria, and rhizobia are three types of nitrogen-fixing bacteria that
occur in symbioses with particular types of plants.
9. How do legumes attract rhizobia?
a. They secrete flavonoids.
b. They secrete carotenoids.
c. They secrete alkaloids.
d. They secrete Nod factors.
e. none of the above
Answer: Legume roots attract soil rhizobia by secreting flavonoids that bind to receptors in the cell
membranes of the bacteria.
10. Which plant uses a passive trap to obtain animal prey as a source of mineral nutrients?
a. the Indian pipe (Monotropa uniflora)
b. the tropical pitcher plant (Nepenthes spp.)
c. the Venus flytrap (Dionaea muscipula)
d. dodder (Cuscuta spp.)
e. all of the above
Answer: b. The pitcher plant Nepenthes uses a passive trap to obtain animal prey.
Conceptual Questions
1. Why are agricultural experts and ecologists alike concerned about overfertilization of crop fields?
Answer: Agricultural experts are concerned that adding excess fertilizer to crop fields increases the
costs of crop production. Ecologists are concerned that excess fertilizers will wash from crop fields into
natural waters and cause harmful overgrowths of cyanobacteria, algae, and aquatic plants. Methods for
closely monitoring crop nutrient needs so that only the appropriate amount of fertilizer is applied would
help to allay both groups’ concerns.
2. How do plant roots acquire enough boron to serve essential needs without transporting toxic
amounts of this mineral to shoots?
Answer: Boron deficiency induces the expression of a gene that encodes a membrane transporter
protein that moves boron from living root cells into root xylem for transport throughout the plant. This
action helps to reduce boron deficiency in plant tissues. When plants are exposed to too much boron,
the transporter protein is removed from root cell membranes, with the result that boron cannot move into
the xylem and the rest of the plant. This action protects the plant from boron toxicity.
3. What are the evolutionary implications of the finding that early steps in the establishment of
mycorrhizal and rhizobia symbioses by the legume Medicago trunculata involve similar genes,
proteins, and signal transduction processes?
Answer: These similarities, coupled with the occurrence of fossil evidence for very early mycorrhizal
relationships, suggest that legume-rhizobial symbioses arose by descent with modification, a general
evolutionary principle.
Experimental Questions
1. Why did Hammond and colleagues seek to identify genes whose expression changed between 24
and 72 hours after plants experience phosphorus limitation?
Answer: During this period of time, the amount of phosphorus in plant tissues had significantly
decreased, but plant growth had not yet been affected. Thus, a monitoring system based on gene
expression changes occurring during this time would allow farmers time to apply fertilizer in order to
prevent crop losses resulting from nutrient deficiency.
2. What advantage do plants obtain when the SQD1 gene is expressed?
Answer: SDQ1 expression is induced by phosphorus deficiency. This gene fosters replacement of
plastid phospholipids with sulfur-containing lipids, thereby reducing the plant’s phosphorus requirement.
3. How were the investigators able to identify plants that were starting to experience phosphorus
deficiency?
Answer: They used genetic engineering techniques to place a reporter gene under the control of the
SQD1 promoter, so that when SQD1 was expressed, the reporter gene was expressed also. After
growing plants in nutrient solutions containing various levels of phosphorus, they removed sample
leaves and treated them with a compound that turns blue when the reporter gene is expressed. When
they saw blue leaves, the investigators could infer: (1) that the plants from which those leaves had been
taken were beginning to experience phosphorus deficiency, and (2) that application of fertilizer at this
point could prevent damage to the plants.
Collaborative Questions
1. Imagine that you have bought a farm and want to start growing a crop to sell at a local market. How
could you go about determining if the soil needs to be fertilized and with what mineral nutrients?
Answer: You could start by deciding what kind of crop you want to grow and then research the mineral
nutritional needs of that crop. Then you would have the soil analyzed to determine if the soil is deficient
in one or more minerals, and apply the appropriate amount and type of organic or inorganic fertilizer. If
the soil is deficient in nitrogen, you might choose to first grow a crop of clover or alfalfa, legumes whose
symbiotic rhizobia enrich the soil with fixed nitrogen.
2. Imagine that you own a large farm through which runs a trout stream. How would you protect the
water quality of the stream?
Answer: You could plant native vegetation along the edges of the stream. The vegetation would not only
foster native wildlife, but also absorb nutrients in rainwater draining from your crop fields. This action
would reduce the amount of minerals that enters the stream, and thereby prevent the formation of
harmful growths of cyanobacteria, algae, and aquatic plants. In addition, you could monitor the fertility
status of your crop fields by having the soil tested for the mineral nutrient levels your crops require.
Then you could apply the minimal amounts of fertilizer needed to supply the needs of your crops. This
action would help to prevent excess minerals from washing into the stream and save you money.