Two groups of tomatoes were grown under laboratory conditions, one with humus added to the soil and one as 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.

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.

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.

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?