Soil Microbiology

Question 1

Ecosystem

Answer 1

The sum of all organisms & abiotic factors in a particular environment

Question 2

Habitat

Answer 2

Portion of an ecosystem where a community could reside

Question 3

Population

Answer 3

Group of microorganisms of same species residing in same place at same time

Question 4

Community

Answer 4

A group of populations

Question 5

Species richness

Answer 5

The total number of different species present

Question 6

Species abundance

Answer 6

The proportion of each species in an ecosystem

Question 7

Guild

Answer 7

Metabolically related microbial populations

Question 8

Niche

Answer 8

Habitat shared by a guild

Question 9

Prime niche

Answer 9

Niche in which the organism is most successful

Question 10

Microenvironment

Answer 10

The immediate environmental surroundings of a microbial cell or group of cells
* Physiochemical conditions are subject to rapid change
* Resources in natural environments are highly variable

Question 11

Parasitism

Answer 11

one member in the relationship is harmed and the other benefits

Question 12

Mutualism

Answer 12

both species benefit

Question 13

Commensalism

Answer 13

one species benefits and the other is neither harmed nor helped

Question 14

Biogeochemical cycle

Answer 14

Transformation of key elements by biological and chemical agents

Question 15

Soil

Answer 15

Loose outer material of Earth’s surface

Question 16

Types of Soil

Answer 16

• Mineral soil
• Organic soil

Question 17

Mineral soil

Answer 17

Derived from rock weathering and other inorganic materials

Question 18

Organic soil

Answer 18

Derived from sedimentation in bogs and marshes

Question 19

Soil composition

Answer 19

• Inorganic material (40%)
• Organic material (5%)
• Air and water (50%)
• Living organisms (5%)

Question 20

Soil structure

Answer 20

• O Horizon:
• A Horizon:
• B Horizon:
• C Horizon:

Question 21

O Horizon

Answer 21

Layer of undecomposed plant materials – top layer

Question 22

A Horizon

Answer 22

Surface soil rich in organic material, full of life

Question 23

B Horizon

Answer 23

Subsoil made of decomposed organic material and humus

Question 24

C Horizon

Answer 24

Soil base which develops directly from underlying bedrock

Question 25

Water availability of different soils

Answer 25

* Sand: Water drains quickly * Silt: Retains water to the right extent * Clay:Water retained too well, and soil becomes anoxic

Question 26

Most important factors influencing microbial activity in soil

Answer 26

* The availability of water in surface soils * Nutrient availability in subsurface soils

Question 27

Functions of bacteria/Archaea in soil

Answer 27

* Production of the humus * Release of minerals from soil particles * Cycling of nutrients (C, N, S) * Nitrogen fixation

Question 28

Rhizospere

Answer 28

Soil that surrounds plant roots and receive plant secretions

Question 29

Nitrogen fixation | Start/End product? Enzyme? Conditions? Electrons required?

Answer 29

* Conversion of atlospheric nitrogen (N2) into ammonia (NH3) * Reaction is catalyzed by nitrogenase complex * Dinitrogenase reductase is inhibited by the presence of oxygen * Requires 8 electrons

Question 30

Free-living nitrogen fixers

Answer 30

Clostridium, Azotobacter, Cyanobacteria

Question 31

Clostridium

Answer 31

strict anaerobe

Question 32

Azotobacter

Answer 32

Strict aerobe * Very high rate of O2 consumption keeps the intracellular environment anaerobic

Question 33

Cyanobacteria

Answer 33

Nitrogen fixation occurs in specialized anaerobic cells (heterocysts) which lack Photosystem II

Question 34

Adaptations of heterocyts

Answer 34

* Thick cell wall that slow down the diffusion of O2 * The regular cells provide the heterocysts with carbohydrate

Question 35

Symbiotic nitrgen fixers

Answer 35

* Colonization of legume roots * Formation of root nodules that fix nitrogen

Question 36

Nodule formation

Answer 36

1. Recognition & attachment of bacterium to root hairs 2. Excretion of nod factors by the bacterium 3. Bacterial invasion of the root hair 4. Travel to the main root via the infection thread 5. Formation of bacteroid state within plant cell 6. Continued plant and bacterial division, forming the mature root nodule

Question 37

O2 regulation in root nodules

Answer 37

Oxygen levels are controlled by leghemoglobin, produced by plant cells