35. Soil

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.

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.

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.

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?

The carnivorous plant Nepenthes bicalcarata ('fanged pitcher plant') has a unique relationship with a species of ant—Camponotus schmitzi ('diving ant'). The diving ants are not digested by the pitcher plants, but instead live on the plants and consume nectar. Diving ants also dive into the digestive juices in the pitcher, swim to the bottom, and capture and consume trapped insects, leaving uneaten body parts and ant feces behind. What nutritional impact do the ants have on fanged pitcher plants? Do the pitcher plants derive any nutritional benefit from this relationship? Nitrogen is a key nutrient often obtained by carnivorous plants from the insects they digest. Are the results presented here what would be expected if nitrogen is a limiting nutrient? Explain.

The carnivorous plant Nepenthes bicalcarata ('fanged pitcher plant') has a unique relationship with a species of ant—Camponotus schmitzi ('diving ant'). The diving ants are not digested by the pitcher plants, but instead live on the plants and consume nectar. Diving ants also dive into the digestive juices in the pitcher, swim to the bottom, and capture and consume trapped insects, leaving uneaten body parts and ant feces behind. What nutritional impact do the ants have on fanged pitcher plants? Do the pitcher plants derive any nutritional benefit from this relationship? Carnivorous plants and legumes (e.g., peas, soybeans) both absorb key nutrients directly from other organisms. How is nutrient acquisition in pitcher plants similar to that in legumes? How is it different?