scsc 301 exam 2 tamu smith(Questions
& Answers 100% Correct!!
an organism that can use CO2or CO3- (i.e., inorganic C) as a C source, and obtain energy from the sun
(photo) - or from the oxidation of inorganic elements or compounds such as iron, sulfur, hydrogen,
ammonium, and nitrites (chemo)? - ANSWERAutotroph such as plants, algae, cyanobacteria, etc.
an organism that can only get carbon and energy from organic compounds? - ANSWERHeterotroph
such as bacteria, fungi, protozoa, etc.
an organism that grows only in the presence of molecular oxygen? - ANSWERaerobe such as
nitrifying bacteria
an organism that only grows in the absence of molecular oxygen? - ANSWERAnaerobe such as
archaea, denitrifying bacteria, some N-fixing bacteria
an organism capable of both aerobic and anaerobic metabolism? - ANSWERfacultative anaerobe
What functions do microorganisms provide in soil? - ANSWER-soil organic matter stabilization,
organic matter mixing, and aggregate formation
-breakdown of toxic compounds
-inorganic transformations: nutrient cycling
-nitrogen fixation
-plant protection
protozoa - ANSWERmobile, single-celled bacterial predators; amoeba, ciliate, flagellates; moist, well-
aerated surface soils
Algae - ANSWERphotosynthetic, autotrophs, primary producers; wet surface soils; can form
symbiotic relationship with fungi to form lichen
Fungi - ANSWEReukarytoes, heterotrophic, diverse morphology, moist environments; can be single-
celled yeasts, filamentous molds or mushrooms with macroscopic fruiting bodies
, Bacteria - ANSWERprokaryotes, most abundant and diverse in soils; important for many soil
functions(bioremedation, decomposition, nutrient cycling)
Actinomycetes - ANSWERfilamentous bacteria (branching morphology), aerobic hetertrophs, non-
acidic, moist, high C environments; produces antibiotics compounds, some fix N especially in forests
(frankia sp.)
Rhizobia - ANSWER-N-fixing bacteria
-Forms root nodules in leguminous plants
-important in grasslands and agricultural systems
mycorrhizal fungi - ANSWERsymbiotic with plants, gets C from plant roots, provides water and
nutrients especially Phosphorous to plants
-provide protection to plants
Saprotrophic fungi - ANSWERgets C from ecosystem, degrades organic matter, important for lignin
degradation and SOM decomposition
Prime conditions for high microbial activity - ANSWER-Carbon availability
-quality C:N
-oxygen availability (greatest zone of activity is top 5 cm of soil bc good balance of O and H20
-Good temperature is 20C-40C
-High calcium and neutral pH soils
-bacterial diversity increases with soil pH (acidic to alkaline soils)
plant roots - ANSWERrelease C into soil via exudates, aid in aggregate formation, use O2 for
respiration (produce CO2)
Earthworms - ANSWEReat detritus (waste), organic matter and microorganisms, form burrows,
"nature's tiller" create casts- aggregation
termites - ANSWERcomplex social colonies, mound builders, symbiotic gut microbes degrade
cellulose, fungi farmers
