Exam 11: Organisms and Ecology of the Soil

Earthworms generally are most abundant in sandy,acid soils typically under coniferous forest vegetation.

Oxidation or reduction of inorganic soil constituents such as iron and sulfur is carried out by members of which group(s)of microorganisms.

Vesicles and arbuscules are structures typically formed ____.

Actinomycetes tend to dominate soils that are either very acid,very cold,or very dry.

Which of the following groups is not considered to include important primary consumers in the soil ecosystem?

Most soil organisms are heterotrophs.

Soil microorganisms often compete with higher plants for mineral nutrients,such as nitrogen.

Many members of which group of soil microorganisms are anaerobic heterotrophs?

Members of this (these)microbial group(s)are responsible for a major proportion of the nitrogen fixed globally in symbiosis with higher plants.

In most soils the overall population (numbers)of microorganisms changes with time,generally following changes in the _____.

This (these)group(s)of microorganisms usually predominate(s)in sandy,acid soils.

In which situation are the actinomycetes likely to be most dominant?

Organisms which use carbon dioxide or carbonates for their carbon source and either sunlight or inorganic chemicals for their energy source are called ____.

In nature,beneficial mycorrhizae form with the roots of _____.

An organism that subsists by eating predators would function as a(n)_____ in the soil ecosystem.

Mycorrhizae do not normally kill their host plants,but merely reduce the efficiency of the plant root system.

Where conditions are favorable,earthworms are known to add several hundred kg/ha of several important nutrients to the soil system.

Of all the groups of soil organisms,bacteria have the most diverse metabolic capabilities.

Disease suppressive soil often results from _____.

Mycorrhizae involve a symbiotic combination of certain bacteria and plant cells.