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

Accepted Answer

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

Accepted Answer

Iron and sulfur oxidation/reduction is mainly carried out by bacteria, including iron-oxidizing bacteria and sulfur-reducing bacteria. Actinomycetes and fungi are not traditionally known for playing major roles in these processes.

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)

Accepted Answer

Adding organic materials to the soil that stimulate diverse microorganisms is the best way to create disease suppressive soil as it promotes the growth of beneficial microorganisms that can help suppress soil-borne diseases. Fumigation with a volatile chemical and heating the soil by natural solarization or steam heat can also be effective but may have negative environmental impacts. Repeated tillage to keep the soil bare for at least one full year is not recommended as it can lead to soil erosion and compaction.

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

Accepted Answer

The population of microorganisms in soils is closely tied to the supply of organic matter, as they are primarily responsible for breaking down and decomposing these materials. As the amount of organic matter in the soil increases or decreases, the microbial population will respond accordingly.

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

Accepted Answer

Earthworm casts contain more of most plant-available nutrients compared to the bulk soil. This is because earthworms consume and digest organic matter in the soil, breaking it down into its component nutrients, making them more available to plants. The casts are also rich in microbial activity and have a more stable soil structure, which can further enhance plant growth.

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

Accepted Answer

Beneficial mycorrhizae can form with the roots of all types of plants listed, including coniferous trees, grasses, legumes, and broadleaf trees.

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

Accepted Answer

Meso- and macrofauna enhance microbial activity by breaking down plant residues and stimulating the growth of microorganisms, accelerating the decomposition process. They can also physically fragment litter and create more surface area for microbes to colonize, further enhancing decomposition.

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

Accepted Answer

Vesicles and arbuscules are structures formed in root cells by fungi when they form mycorrhizae.

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

Accepted Answer

Actinomycetes and bacteria, particularly those in the genus Rhizobium among bacteria, are known for their role in nitrogen fixation in symbiosis with higher plants. Fungi, while involved in various symbiotic relationships with plants (e.g., mycorrhizae), are not major contributors to nitrogen fixation.

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

Accepted Answer

Actinomycetes prefer neutral pH and moist conditions, and they thrive in organic matter-rich soils. Soil with partially decomposed residues is a perfect environment for their growth and dominance.

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

Accepted Answer

Organisms that use carbon dioxide or carbonates for their carbon source and either sunlight or inorganic chemicals for their energy source are called autotrophs. Facultative anaerobes can use oxygen if it is present, but can also survive without it. Heterotrophs obtain their carbon and energy from organic compounds. Detritivores are organisms that feed on dead organic matter. Actinomycetes are a type of bacteria that can form branching filaments reminiscent of fungi.

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

Accepted Answer

Bacteria, including members of the phyla Firmicutes and Bacteroidetes, are anaerobic heterotrophs commonly found in the soil. Actinomycetes and fungi are aerobic heterotrophs that require oxygen for respiration.

Question 13

Which group of soil organisms includes the largest number of autotrophic species?
A)bacteria
B)fungi
C)actinomycetes
D)detritivores
E)protozoa

Accepted Answer

Bacteria include the largest number of autotrophic species, as they encompass a wide variety of organisms capable of photosynthesis (like cyanobacteria) and chemosynthesis, which are processes that do not require organic compounds for energy.

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

Accepted Answer

The addition of plant residues to the soil promotes the growth of beneficial microorganisms that help suppress soil-borne plant diseases. This is especially true if the plant residues are high in lignin and cellulose, such as straw or corn stalks, which take longer to decompose and provide a longer-lasting source of food and habitat for these microorganisms. Therefore, the correct answer is B, as the addition of plant residues reduces the incidence and severity of soil-borne plant diseases.

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

Accepted Answer

Predators are not considered primary consumers in the soil ecosystem. They are higher up on the food chain and feed on other organisms rather than directly on organic matter in the soil. The other choices listed are all known to function as primary consumers in the soil ecosystem.

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

Accepted Answer

The answer of This (these) group(s) of microorganisms usually predominate(s)...

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

Accepted Answer

Microflora, which includes bacteria and fungi, are responsible for the majority of organic matter decomposition in soils. They are able to break down complex organic compounds into simpler forms that can be assimilated by plants and other organisms. While macrofauna and mesofauna also play a role in soil decomposition, their impact is relatively small compared to microflora. Autotrophs, such as plants and algae, are not directly involved in organic matter decomposition, but they do contribute to the overall health and fertility of soils through their nutrient cycling processes.

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

Accepted Answer

The answer of The fungal symbiont generally benefits from the...

Question 19

Soil detritivores feed principally on ___.
A)smaller organisms
B)plant roots
C)larger, but defenseless animals
D)dead tissues
E)microorganisms

Accepted Answer

Soil detritivores are organisms that feed on dead and decaying organic matter in the soil, such as fallen leaves, dead bark, and dead animals. Therefore, the best choice is D - dead tissues.

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

Accepted Answer

A tertiary consumer is an organism that eats other consumers, including predators. In the soil ecosystem, this would likely include organisms such as nematodes or mites that eat larger predators such as centipedes or spiders.

Quiz 11: Organisms and Ecology of the Soil

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

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

Disease suppressive soil often results from _____.

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

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

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

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

Vesicles and arbuscules are structures typically formed ____.

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

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 ____.

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

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

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

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

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

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

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

Soil detritivores feed principally on ___.

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