35. Soil

How might roots react when they encounter a region of the soil that is low in nitrates?

The American Dust Bowl of the 1930s resulted from __________.

Soil can easily become deficient in __________ because these ions are negatively charged and do not stick to negatively charged soil particles.

The particles in soil are important because they __________.

Fertilizers are usually enriched in __________.

Which of the following would be considered a sustainable agricultural practice?

What is the goal of phytoremediation?

Why do farmers need to be concerned with the pH level of soil?

At low soil pH levels (5 or less), what can happen?

Phytoremediation is showing promise as a sustainable, cost-effective way to decontaminate soil and water. In the case of a hyperaccumulater such as Thlaspi caerulescens, however, what might be a drawback of the technology?

The biological process that produces 96% of the dry mass of a plant is called __________.

Which of the following substances does a plant obtain from the air?

A botanist claims to have discovered a new macronutrient required for plant growth. Most of this scientist's colleagues are skeptical of her claim. Why might they consider it unlikely?

If a plant's leaves are yellowing, it may be that the plant is deficient in the elements needed to make chlorophyll, one of which is __________.

If a plant is deficient in __________, it will not be able to make DNA.

Soil could be deficient in any of the following nutrients. If you had to supply one of them, which would be needed in the smallest amount?

Which of the following is a true statement regarding mineral deficiency symptoms in plants?

When you add "plant food" to your potted geraniums, what are you actually providing the plant with?

How did the addition of a gene for citrate synthesis increase the tolerance of tobacco and papaya plants to high aluminum concentrations in the soil?

What supplies the energy for most of the microorganisms in the rhizosphere?

The inorganic nutrient most often lacking in crops is a. carbon. b. nitrogen. c. phosphorus. d. potassium.

Consider the following statements regarding limiting nutrients. Select True or False for each statement. T/F Nitrogen (N), phosphorus (P), and potassium (K) are common examples. T/F Their presence limits the availability of micronutrients. T/F Their availability tends to limit plant growth. T/F Certain macronutrients and micronutrients can be considered limiting nutrients.

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.

Where is the start codon located? a. at the start (5′ end) of the mRNA b. in the DNA just upstream of where transcription starts c. at the downstream end of the 5′ untranslated region (UTR) d. at the upstream end of the 3′ untranslated region (UTR)

Plants require the smallest amount of which of the following nutrients? a. oxygen b. phosphorus c. carbon d. iron

Where does most nutrient uptake occur in roots? a. at the root cap, where root tissue first encounters soil away from the zone of nutrient depletion b. at the Casparian strip, where ions must enter the symplast before entering xylem cells c. in the symplastic and apoplastic pathways d. in root hairs, in the zone of maturation

Why are proton pumps in root-hair plasma membranes important? a. They pump protons into cells, generating a membrane potential (voltage). b. They allow toxins to be concentrated in vacuoles, so the toxins do not poison enzymes in the cytoplasm. c. They set up an electrochemical gradient that makes it possible for roots to absorb cations and anions. d. They set up the membrane voltage required for action potentials to occur.

Why is the presence of clay particles important in soil? a. They provide macronutrients—particularly nitrogen, phosphorus, and potassium. b. They bind metal ions, which would be toxic if absorbed by plants. c.They allow water to percolate through the soil, making oxygen-rich air pockets available. d. The negative charges on clay bind to positively charged ions and prevent them from being leached out of the soil.

. A problem with intensive irrigation is (A) overfertilization. (B) aquifer depletion. (C) the long-term depletion of soil oxygen. (D) the clogging of waterways by vegetation debris.

Some of the problems associated with intensive irrigation include all of the following except a. soil salinization. b. overfertilization. c. land subsidence. d. aquifer depletion.

An advantage of using fertilizers derived from natural sources is that these fertilizers a. have different minerals than artificial fertilizers. b. are retained in soil longer. c. are more soluble in water. d. are more concentrated.

Suppose that certain root cells have an overall charge that is more negative than normal. What impact would this likely have on the uptake of anions such as NO3−? a., Anions would be less likely to enter roots. b. Anions would be more likely to enter roots. c. This would have no impact on the ability of anions to enter roots. d. This would make anions and cations equally likely to enter roots.

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.

In a semester-long experiment tracking growth in plants, your lab partner—who often skips class—carefully records the mass of water added to a potted plant with the expectation that this addition will be fully accounted for in the mass gained by the plant. Is your lab partner right or wrong? Explain.

Your friend claims that all plants are autotrophs because they perform photosynthesis. Is that a correct statement? Explain.

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 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.

In what ways are a promoter and a start codon similar? In what ways are they different?

Why is it important for plants to exclude certain ions? Summarize the difference between active and passive exclusion mechanisms.

If the apples you buy are labeled 'organic,' does that tell you anything about how they were grown? About the nutritional content of the apples?

There is a conflict between van Helmont's data on willow tree growth and the data on essential nutrients listed in Table 36.1. According to the table, nutrients other than C, H, and O should make up about 4 percent of a willow tree's mass. Most or all of these nutrients should come from soil. But van Helmont claimed that the soil in his experiment lost just 60 g, while the tree gained 74,000 g. Calculate the percentage of the added mass accounted for by soil, and compare it to the predicted 4 percent. State at least one hypothesis to explain the conflict between expected and observed results. How would you test this hypothesis?

DRAW IT Draw a simple sketch of cation exchange, showing a root hair, a soil particle with anions, and a hydrogen ion displacing a mineral cation.

Acid rain contains an excess of hydrogen ions (H+). One effect of acid rain is to deplete the soil of plant nutrients such as calcium (Ca2+), potassium (K+), and magnesium (Mg2+). Offer a hypothesis to explain why acid rain washes these nutrients from the soil. How might you test your hypothesis?

SCIENTIFIC THINKING One of the most important properties of proper scientific investigations is their repeatability. Yet, as discussed in Module 32.11, studies that compare the nutritional content of conventional and organic produce sometimes produce contradictory results. Name some possible confounding factors that can account for such uneven results.

Toxins like αα-amanitin are used for research in much the same way as null mutants (Chapter 16)—to disrupt a process and see what happens when it no longer works. Researchers examined the ability of αα-amanitin to inhibit different RNA polymerases. They purified RNA polymerases I, II, and III from rat liver, incubated the enzymes with different concentrations of αα-amanitin, and then tested their activity. The results of this experiment are shown here. These findings suggest that cells treated with αα-amanitin will have a reduced level of: a. tRNAs b. rRNAs c. snRNAs d. mRNAs

If you wanted to use αα-amanitin to shut down 95 percent of transcription by RNA polymerase II, roughly what concentration of αα-amanitin would you use? Note that the scale on the x-axis of the graph in Question 13 is logarithmic rather than linear, so that each tick mark shows a tenfold higher concentration.