Soil Microbiology

Question 1

ecosystem

Answer 1

the sum of all organisms and abiotic factors in a particular environment. Complex of plants, animals, abiotic, and microbial communities which interact as a *functional unit

Question 2

habitat

Answer 2

portion of an ecosystem where a community could reside. An ecosystem contains many different habitats.

Question 3

population

Answer 3

group of microorganisms of the same species residing in the same space

Question 4

community

Answer 4

group of populations

Question 5

species richness

Answer 5

total number of different species present

Question 6

species abundance

Answer 6

the proportion of each species in an ecosystem (amount of individuals in each species)

Question 7

guild

Answer 7

metabolically related microbial populations.

Question 8

niche

Answer 8

habitat shared by a guild. It supplies nutrients and conditions for growth

Question 9

microenvironment

Answer 9

• the immediate environmental surroundings of a microbial cell or group of cells.
• soil particles contain many microenvironments

Question 10

competition and cooperation

Answer 10

occur between microbes in natural systems and between microbes and higher organisms.

Question 11

parasitism, mutualism, commensalism

Answer 11

many microbes establish relationships with other organisms

Question 12

biogeochemistry

Answer 12

the study of biologically mediated chemical transformations

-biogeochemical cycles

Question 13

mineral soils

Answer 13

derived from rock weathering and other inorganic materials.

Question 14

organic soils

Answer 14

derived from sedimentation in bogs and marshes

Question 15

composition of soil

Answer 15

• air and water
• inorganic mineral matter
• organic matter
• living organsims

Question 16

humus

Answer 16

dead plant material that is resistant to decomposition

• keeps water and nutrients in the soil
• good for soil fertility

Question 17

top few centimeters of soil contain..

Answer 17

**bacteria: up to 2.5x10^9 (*per g of soil)

Question 18

rhizosphere

Answer 18

soil that surrounds plant roots and receive plant secretions

Question 19

mycorrhizae

Answer 19

association of fungi with plant roots

Question 20

**Azotobacter

Answer 20

• widespread in soil, require a soil rich in organic matter to provide energy for nitrogen fixation
• produce ammonia that can be used in plants (NH3 dissolves in water to produce NH4)

Question 21

Nitrogen fixation

Answer 21

• only certain prokaryotes can fix N2 because a lot of energy is required to break the triple bond
• ammonia is the final product and used to produce amino acids
• **Dinitrogenase reductase is inhibited by the presence of oxygen

Question 22

Nodule formation

Answer 22

1. recognition and attachment of bacterium to root hairs
2. excretion of *node factors by the bacterium
3. bacterial invasion of the root hair
4. travel to the main root via the infection thread (tube composed of cellulose)
5. formation of *bacteroid state *within plant cell (swollen and misshapen bacteria fix N2). Surrounded by plant cytoplasm
6. continued plant and bacterial division, forming the mature root nodule

Question 23

Cyanobacteria

Answer 23

• nitrogen fixation in heterocysts (anaerobic) that do not have photosystem II.
• heterocysts have a thick cell wall and slow diffusion of O2

Question 24

symbiosis and nitrogen fixers

Answer 24

-leguminous plants and bacteria