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.

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

The specific relationship between a legume and its mutualistic Rhizobium strain probably depends on:

a. Each legume having a chemical dialogue with a fungus

b. Each Rhizobium strain having a form of nitrogenase that works only in the appropriate legume host

c. Each legume being found where the soil has only the Rhizobium specific to that legume

d. Specific recognition between chemical signals and signal receptors of the Rhizobium strain and legume species

Draw a simple sketch of cation exchange, showing a root hair, a soil particle with anions, and a hydrogen ion displacing a mineral cation.

The greatest difference in health between two groups of plants of the same species, one group with mycorrhizae and one group without mycorrhizae, would be in an environment

a. Where nitrogen-fixing bacteria are abundant

b. That has soil with poor drainage

c. That has hot summers and cold winters

d. In which the soil is relatively deficient in mineral nutrients

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.