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.

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.

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.