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

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?

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?