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What is an ecosystem?
The sum of all organisms and abiotic factors in a particular environment. An ecysystem is a dynamic complex of plant, animal and microbial communities and the nonliving surroundings, which interact as a functional unit
What is a habitat?
Portion of an ecosystem where a commjnity could reside. Many habitats are unsuitable for plants and animals and some habitats are almost exclusively
What is a population?
Group of microorganism of the same sepcies residing in the same pace at the same time
What is a community?
A group of a population
What are the two different ways in which diversity of a microbial species in an ecosystem can be expressed?
- Species richness
- Species abundance
What does species richness refer to?
The total number of different species present
What does species abundance refer to?
The propertion of each species in an ecosystem
What are microbial species richness and abundance a function of?
Microbial species richness and abundance is a function of the kinds and amounts of nutrients available in a give habitat
What are guilds?
Metabolically related microbial populations. Sets of guilds form microbial communities that interact with macroorganisms and abiotic factors in the ecosystem
What is a niche?
Habitat share by a guild. Supplies nutrients as well as conditions for growth
What does the growth of microbes depend on?
The growth of microbes depends on resources and growth conditions
What is a microenvironment?
- The immediate environmental surroundings of a microbial cell or group of cells
- Soil particles contain many microenvironments
Describe the physiochemical conditions in microenvironments
Physiochemical conditions in a microenvironment are sunject to rapid change, both spatially and temporally
What is parasitism?
One member in the relationship is harmed and the other benefits
What is mutualism?
Both species benefit (symbiosis)
What is commensalism?
One species benefits and the other is neither harmed nor helped
What is biogeochemistry?
The study of biological mediatd chemical transformations
What is a biogeochemical cycle?
A biogeochemical cycle defines the transformations of a key element by biological and chemical agents
What are the major end products of the carbon cycle?
CH4 and CO2
What organisms are the foundation of the carbon cycle?
What is the most stable form of nitrogen?
What is denitrification?
The reduction of nitrate into gaseous nitrogen products and is the primary mechanism by whith H2 is produced biologically
What is the most abundant organic slfur compound in nature?
- Dimethyl sulfide
- Produced primarily in marine environments as a degradation product of dimethylsulfoniopropionate
- DMS can be transformed via a number of microbial processes
What is soil?
The loose outer material of Earth's surface, distinct from bedrock
What are the two broad groups soil can be divided into?
- Mineral soils
- Organic soils
What are mineral soils?
Derived from rock weathering and otther inorganic materials
What is organic soils?
Deried from sedimentation in bogs and marshes
What are soils composed of?
- Inorganic mineral matter (~40% of soil volume)
- Organic matter (~5%)
- Air and Water (~50%)
- Living organisms
What is the O horizon of soil?
Layer of undecomposed plant materials
What is the A horizon of soil?
Surface soil (high in organic matter, dark in color, is tilled for agriculture; plants and large numbers of microorganisms grow here; microbial activity high)
What is the B horizon of soil?
Subsoil (minerals, humus and so on, leached from soil surface accumulate here; little organic matter; microbial activity detectable but lower than at A horizon)
What is the C horizon of soil?
Soil base (develops directly from underlying bedrock; microbial activity generally very low)
What is the most important factor in subsurface environments?
Where does most microbial growth take place in soil?
On the surface of soil particles
What is the most important factor influencing microbial activity in soil?
What happens to water in sand?
It drains quickly
What happens to water in silt?
Retains water to the right extent
What happens to water in clay?
Water retained too well, soil becomes anoxic
What are prokaryotes largely responsible for in soil?
- The production of humus
- Release of minerals from soil particle (Production of acids from organic compounds solubilize the minerals)
- Cycling of nutrients
- Nitrogen fixation
What is the rhizosphere?
Soil that surrounds plant roots and recieve plant secretions
What is a mycorrhizae?
Association of fungi with plant roots?
What is nitrogen fixation catalyzed by?
nitrogenase complex (metal cofactors)
What is the final product of nitrogen fixation?
Ammonia, ued to produce amino acids
What are some examples of free-living nitrogen fixers?
Azotobacter, Beijerinckia, Clostridium
Where are free-living nitrogen fixers found?
Widespread in soil, require a soil rich in organic matter to provide energy for nitrogen fixation
What is Clostridium?
What is Azotobacter?
Strict anaerobes. The enzyme is protected by very high rate of O2 consumption, which keeps the intracellular environment anaerobic
What is cyanobacteria?
Only some species are capable of N2 fization. MAJOR nitrogen-fixing organism in nature. Cyanobacteria produce energy by oxygenic photosynthesis, oxygen is produced in the cell
Where does nitrogen fixation occur within cyanobacteria?
Nitrogen fixation occurs in specialized anaerobic cells (heterocysts), which lact PTSII, and produce ATP by cyclic photophosphorylation
What is special about hetercysts?
They have thick cell walls that slow the diffusion of O2
What is symbiotic nitrogen fixers?
The mutulastic relationship between legumious pabts and nitrogen-fixing bacteria is one of the most important symbioses known
What are the steps of nodule formation?
- Step 1: recognition and attachment of bacterium to root hairs
- Step 2: excretion of nod factors by the bacterium
- Step 3: bacterial invasion of the root hair
- Step 4: Travel to the main root via the infection thread (tube composed of cellulose)
- Step 5: Formation of bacteroid state within plant cells (swollen and misshapen bacteria-fix N2)
- Step 6: Continued plant and bacterial division, forming the mature root nodule
How are O2 levels in nodules controlled?
O2 levels are controlled by the O2-binding protein leghemoglobin, produce by the plant cells
What happens if soil is poorly drained?
- If the soil is poorly drained and becomes waterlogged conditions becomes anaerobic, which promotes denitrification
- Anaerobic conditions also promotes sulfur and sulfate reduction which produce H2S (toxic for plants)
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