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

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.

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

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?