Exam 11: Organisms and Ecology of the Soil

Compared to the rest of the soil,the rhizosphere is kept relatively sterile by the action of plant roots.

Algae are single-celled plants that function principally as primary producers in the soil ecosystem.

Meso- and macrofauna contribute to organic matter decomposition primarily by ______.

Certain soil fungi and actinomycetes are known to produce specialized organic compounds that inhibit or kill other,competing microorganisms in the soil,but so far scientists have not been able to put any of these compounds to practical use.

The total number of microorganisms in a hectare of soil is far greater than the number of macroorganisms,but the reverse is true for biomass of the two groups.

A significant portion of the global production of methane comes from the activity of termites.

Mucigel is thought to improve the contact between plant roots and soil particles,thus enhancing the plant uptake of water and nutrients.

Which group of soil organisms includes the largest number of autotrophic species?

All but a few nematodes are pests,attacking either economic or wild plants.

Research has shown that most herbicides and insecticides used in agriculture drastically reduce the numbers of living meso- and microorganisms in soils for several years after the application of these chemicals.

Termites tend to enrich soils in the tropics much the same way as earthworms do in temperate region soils.

Fungi tend to be the dominant group of microorganisms in acid,sandy soils.

Soil detritivores feed principally on ___.

Plant roots are an important source of carbon for many soil organisms which are beneficial to plants.

The fungal symbiont generally benefits from the mycorrhizal relationship by obtaining ____ from the higher plant.

Which of the following groups of organisms are responsible for greatest amount of organic matter decomposition in soils?

The deeper that they are placed in the soil,the more rapidly organic compounds such as pesticides are decomposed by the soil microflora.

Most anaerobic organisms in soils are bacteria.

Which of the following organisms can commonly be seen with the unaided eye in organic matter-rich soils?

The addition of large quantities of plant residues to the soil generally ____ the incidence and severity of soil-borne plant diseases.