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

Mycorrhizae enhance plant nutrition mainly by:

a. Absorbing water and minerals through the fungal hyphae

b. Providing sugar to root cells, which have no chloroplasts

c. Converting atmospheric nitrogen to ammonia

d. Enabling the roots to parasitize neighboring plants

Which of the following activities of soil bacteria does not contribute to creating usable nitrogen supplies for plant use?

a. The fixation of atmospheric nitrogen

b. The conversion of ammonium ions to nitrate ions

c. The decomposition of dead animals

d. The assembly of amino acids into proteins

Epiphytes are:

a. Fungi that attack plants

b. Fungi that form mutualistic associations with roots

c. Nonphotosynthetic parasitic plants.

d. Plants that grow on other plants.

By trapping insects, carnivorous plants obtain ___________, which they need ___________ . (Choose the best answer.)

a. Water ... because they live in dry soil

b. Nitrogen ... to make sugar

c. Phosphorus ... to make protein

d. Nitrogen ... to make protein

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

Design an experiment, using radioactive carbon and the heavy isotope of nitrogen (15N₂), that would test whether the Rhizobia–pea plant interaction is mutualistic.

The allele of the human transport protein associated with lighter skin is found almost exclusively in people with European ancestry. The other common allele for darker skin, which appears to be the ancestral allele, is found in people with African ancestry. What is a plausible explanation for how the lighter-skin allele came to be so common in those with European ancestry?