35. Soil

An advantage of using fertilizers derived from natural sources is that these fertilizersa. 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 ifa. 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 thata. 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. tRNAsb. rRNAsc. snRNAsd. 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.