Deck 11: Organisms and Ecology of the Soil

Question 1

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

A)fungi
B)bacteria
C)Nematodes
D)actinomycetes
E)none of the above

Answer 1

A

Question 2

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

A)actinomycetes
B)bacteria
C)fungi
D)A and C
E)all of the above

Answer 2

B

Question 3

Disease suppressive soil often results from _____.

A)Fumigation with a volatile chemical.
B)Heating the soil by natural solarization or steam heat.
C)Repeated tillage to keep the soil bare for at least one full year.
D)Adding organic materials to the soil that stimulate diverse microorganisms.
E)All of the above.
True or False Questions
(Write T or F after each statement)

Answer 3

D

Question 4

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

A)supply of decomposable organic matter
B)supply of oxygen
C)porespace
D)availability of root infection sites
E)concentrations of antibiotics

Question 5

Compared to the bulk soil in which the earthworms live, earthworm casts contain ____.

A)less of most plant-available nutrients
B)more nitrogen but less of other plant-available nutrients
C)more of most plant-available nutrients
D)more sand and silt
E)less organic matter

Question 6

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

A)coniferous trees
B)grasses
C)legumes
D)broad leaf trees
E)all of the above

Question 7

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

A)enzymatic digestion of plant residues
B)enhancement of microbial activity
C)predation
D)synthesis of humus
E)none of the above

Question 8

Vesicles and arbuscules are structures typically formed ____.

A)in bacterial cells when attacked by protozoa.
B)above ground by certain soil fungi
C)by mesofauna when they incorporate organic materials into the soil
D)in root cells by fungi when they form mycorrhizae
E)none of the above

Question 9

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

A)actinomycetes
B)bacteria
C)fungi
D)A and B
E)all of the above

Question 10

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

A)extremely acid conditions too severe for most other microorganisms
B)low organic matter soils
C)cold, wet soils
D)soil with lots of fresh, easily decomposed residues
E)neutral, moist, warm soil with lots of partially decomposed residues

Question 11

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

A)facultative anaerobes
B)heterotrophs
C)detritivores
D)autotrophs
E)actinomycetes

Question 12

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

A)actinomycetes
B)bacteria
C)fungi
D)both A and C
E)all of the above

Question 13

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

A)bacteria
B)fungi
C)actinomycetes
D)detritivores
E)protozoa

Question 14

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

A)increases
B)reduces
C)has no effect on

Question 15

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

A)detritivores
B)herbivores
C)fungi
D)saprophytes
E)predators

Question 16

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

A)actinomycetes
B)bacteria
C)fungi
D)both A and C
E)all of the above

Question 17

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

A)macrofauna
B)microfauna
C)mesofauna
D)microflora
E)autotrophs

Question 18

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

A)water
B)phosphorus
C)micronutrients
D)A-C
E)none of the above

Question 19

Soil detritivores feed principally on ___.

A)smaller organisms
B)plant roots
C)larger, but defenseless animals
D)dead tissues
E)microorganisms

Question 20

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

A)primary consumer
B)detritivore
C)tertiary consumer
D)decomposer
E)all of the above

Question 21

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

Question 22

Most anaerobic organisms in soils are bacteria.

Question 23

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

Question 24

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.

Question 25

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

Question 26

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

Question 27

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.

Question 28

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

Question 29

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

Question 30

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

Question 31

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

Question 32

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

Question 33

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

Question 34

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

Question 35

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

Question 36

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.

Question 37

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

Question 38

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

Question 39

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

Question 40

Most soil organisms are heterotrophs.

Question 41

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