Module 1

Question 1

What is microbial biomass

Answer 1

Microbial biomass (bacteria and fungi) is a measure of the mass of the living component of soil organic matter. The microbial biomass decompose plant and animal residues and soil organic matter to release carbon dioxide and plant available nutrients.

Question 2

What is organic matter content

Answer 2

Soil organic matter is the organic matter component of soil, consisting of plant and animal detritus at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize.

Question 3

What is oven dried weight

Answer 3

Remaining weight of a soil once moisture and OM have been accounted for.

Question 4

List the basics of soil genesis

Answer 4

Soil genesis is a function of climate, organisms, relief, parent material, and time

Question 5

Where are soil bacteria found

Answer 5

Attached to surface of soil particles, few are found free in soil solution.

Question 6

List soil particle size of textural classes

Answer 6

Sand 2.0 to 0.05 mm
Silt 0.05 to 0.002 mm
Clay <0.002 mm

0.001 mm = 1 um
1 mm = 1000 um

Question 7

What is soil anion and cation exchange capacity + microbes?

Answer 7

Microorganisms bind to negatively charged clay and OM through areas of pos charge (protiens).

Cation exchange capacity (CEC) represents the quantity of negative charge available to attract cations. Anion exchange capacity (AEC) represents the positive charge available to attract anions in solution.

Question 8

What are the three states of soil water potential?

Answer 8

• Saturation soil pores are full of water.
• Field capacity majority of water is gone, esp large pore water
• Wilting point critical point for plants, can no longer extract water

Soil water potential - energy required to pull water from soil. The above describe water content across diff potentials.

Question 9

Which soil solution components affect pH?

Answer 9

Water, dissolved OM, inorganic constituents, O2 and CO2.

Question 10

Describe microbial activity as a function of temperature

Answer 10

Microbial activity increases as the optimal temperature is reached as governed by the laws of thermodynamics. The rate of chemical reactions is a direct function of temp.

Question 11

What is Q10

Answer 11

A measure of the change in enzyme activity (reaction rate) caused by a 10C rise in temp.

Most microbial enzymes have a Q10 of 2.

Question 12

Direct and indirect ways macro, meso, and microfauna interact?

Answer 12

Grazing - decreases microbial biomass
Selective grazing - changes in composition
Nutrient cycling

Habitat engineering - primary production and transport of smaller fauna

Question 13

Difference between detritivores and decomposers

Answer 13

Decomposers subsist on dead plant debris via saprotrophic feeding (fungi and bacteria perform extracellular digestion). Detritivores also subsist on dead plant debris but involves macroscopic swallowing of material.

Question 14

List the 4 classes of soil organisms and an associated type

Answer 14

1. Microflora/orgs - bacteria
2. Microfauna - protozoa
3. Mesofauna - mites
4. Macrofauna - earthworm

Question 15

Photoorganotrophs

Answer 15

Use light as energy source. Use organic compounds as electron donors. Many organic compounds used, depends on functional group of microbe. Eg. bacteria.

Question 15

Photolithotrophs

Answer 15

Use light as energy source. Use inorganic compound (CO2, H2S) as electron donor. Eg. Bacteria

Have oxygenic or anoxygenic photosynthesis.

Question 15

Chemolithotrophs

Answer 15

1. Use chemicals for energy (hydrogen gas, ammonia)
2. Use inorganic substances for electron donors
3. Eg. Archaea

Question 15

What is metabolic classification based on?

Answer 15

1. Source of energy (photo or chemo)
2. Source of reducing equivalents (i.e. electron donor/acceptor)
3. Source of carbon (autotroph or heterotroph)

Question 16

Chemoorganotrophs

Answer 16

1. Use chemicals as source of energy (sugars, fats)
2. Use organic substances for electron donors
3. Eg. most animals and bacteria

Question 17

List 4 methods to measure soil microbial biomass (quantitative)

Answer 17

1. Chloroform-fumigation incubation
2. Chloroform-fumigation extraction
3. Glucose-stimulated respiration
4. Phospholipid fatty acids

Question 18

List life attributes of soil bacteria

Answer 18

-Rapid growth/reproduction
-Min number of 1000 enzymes
-Nutrient uptake optimized by high surface area/volume ratio
-Can outgrow predators

Question 19

List 3 points on composition of bacterial cells

Answer 19

-Water makes most of weight (70-90%)
-Remaining ~30% is ions, molecules, phospholipids, DNA, RNA, proteins and carbs
-Some trace elements

Question 20

List 4 classes of biomolecules

Answer 20

1. Proteins (amino acids)
2. Carbs (sugars)
3. Nucleic acid (DNA)
4. Lipids

Question 21

List the functions of a cell wall

Answer 21

• Protect bacteria from osmotic lysis (bursting)
• Determines and maintains cell shape
• Provides platform for appendages like flagellum
• Does not protect against toxicants

Question 22

What is the structure of a cell wall made of and what two types are there

Answer 22

- Contains peptidoglycan - May be gram+ or gram-

Question 23

Describe the structure and composition of peptidoglycan

Answer 23

Composed of repeating NAG and NAM chains that are linked together by tetrapeptide chains. The links make peptidoglycan a rigid sheet.

Question 24

Define gram positive

Answer 24

Gram+ cell wall is composed of numerous dense layers of peptidoglycan sheets and teichoic acid, lipoteichoic acid, and surface proteins.

Question 25

Define gram negative

Answer 25

Gram- wall is composed of a thin wall of peptidoglycan and an outer membrane as well as a periplasmic space between the outer and inner membrane.

Question 26

Which type of cell wall contains teichoic acid? What is the peptido, and lipid/lipoprotein content of each?

Answer 26

- Gram+ has teichoic acid - Gram+ is >50% and 0-3% for lipids - Gram- is 10-20% and up to 10% lipids

Question 27

Which solutions will identify a gram+ and gram- cell wall after crystal violet and iodine stain the wall violet?

Answer 27

Alcohol will decrease permeability so the pores will trap crystal violet thus remaining violet for gram+. Lipids in gram- will retain permeability and thus the CV will be washed out. After safranin is applied, the gram+ will still be violet but gram- will stain red.

Question 28

Which qualities give gram- a competitive advantage

Answer 28

The outer membrane and the periplasmic space. The outer membrane can defend against toxicants.

Question 29

Why does the periplasmic space give gram- a competitive advantage

Answer 29

This space concentrates the zone of enzyme activity unlike gram+ where enzymes are secreted.

Question 30

What two types of enzymes are in the periplasmic space

Answer 30

Detoxifying enzymes - alter harmful agents before entering the cell Hydrolytic enzymes - part of initial degradation of food molecules

Question 31

When does the charge increase or decrease in redox equations

Answer 31

Oxidation is the loss of electrons (charge increases). Reduction is the gain of electrons (charge decreases). *Remember electrons are negatively charged