Ecology unit 5 quiz

Biogeochemical cycles: Cycling of energy and elements essential for plant and animal growth Reservoirs are where elements are held in [blank_start]large[blank_end] quantities for [blank_start]large[blank_end] periods of time Exchange pool is a [blank_start]dynamic[blank_end] part of a nutrient cycle where element is held for a [blank_start]short[blank_end] period of time Residence time is how long an element is held in a [blank_start]reservoir[blank_end] or [blank_start]exchange[blank_end] pool Energy for nutrient cycles provided by either [blank_start]solar[blank_end] energy or [blank_start]gravity[blank_end] force, [blank_start]meteorites[blank_end] are the only extra-terrestrial sources of elements.

Bioremediation is using microbes to [blank_start]decontaminate[blank_end] soils by degrading organic [blank_start]pollutants[blank_end] or changing toe [blank_start]structure[blank_end] of a pollutant. Soil organic matter is a complex mixture of both plant and animal [blank_start]residues[blank_end] at various stages of [blank_start]decomposition[blank_end]. It contains root [blank_start]exudates[blank_end] and soil [blank_start]microbes[blank_end]. [blank_start]50[blank_end]% of soil is solid made up of [blank_start]inorganic[blank_end] minerals, [blank_start]25[blank_end]% air, [blank_start]20[blank_end]% water and [blank_start]5[blank_end]% living organisms. Water, air and organisms make up [blank_start]pore[blank_end] space.

Soil pores and [blank_start]capillary[blank_end] law: pores that have a diameter [blank_start]smaller[blank_end] than a critical value will be filled with [blank_start]water[blank_end] at a given water [blank_start]potential[blank_end]. Soil [blank_start]atmosphere[blank_end] is strongly influenced by presence of water, root [blank_start]respiration[blank_end] and soil [blank_start]organisms[blank_end]. Oxygen diffuses [blank_start]10,000[blank_end] times slower in [blank_start]water[blank_end] than air in soil. Types of soil organisms present depends on soil [blank_start]aeration[blank_end]. Soil organic [blank_start]matter[blank_end] and soil [blank_start]microbe[blank_end] activity have a role in soil [blank_start]aggregation[blank_end]. Specific [blank_start]compounds[blank_end] produced by soil microbes promote [blank_start]aggregation[blank_end]. Example: Fungi produce [blank_start]glomalin[blank_end] which coats [blank_start]hyphae[blank_end] preventing loss of water and [blank_start]nutrients[blank_end]. Soil aggregation has a key role in microbial [blank_start]activity[blank_end] and organic matter [blank_start]decomposition[blank_end] and turn over

Occurrence and distribution of microbes in soil: Bacteria and algae are considered [blank_start]aquatic[blank_end] as they require [blank_start]substrate[blank_end] and nutrients to be [blank_start]diffused[blank_end] in water for their nutrition. Bacteria prefer to live in pores only slightly [blank_start]larger[blank_end] than them for protection against [blank_start]desiccation[blank_end] and predation. Bacteria can be free living or attached to the surface of [blank_start]particles[blank_end]. When attached they may be [blank_start]individual[blank_end] cells, micro-[blank_start]colonies[blank_end] or bio-[blank_start]films[blank_end]. Less than [blank_start]1[blank_end]% of available pore space is occupied by microbes. [blank_start]Accessibility[blank_end] of pore is determined by [blank_start]neck[blank_end] size. [blank_start]Fungi[blank_end] occupy the same size and larger pores as bacteria, with [blank_start]hyphae[blank_end] extending through [blank_start]unsaturated[blank_end] pores. Soil microhabitats are not always [blank_start]connected[blank_end]. In clay soil [blank_start]52[blank_end]% and in sandy soil [blank_start]15[blank_end]% of pores inaccessible to microbes due to [blank_start]neck[blank_end] size being smaller than [blank_start]0.2[blank_end] microns. Large pores of [blank_start]30[blank_end] microns are filled with [blank_start]air[blank_end]. There is a limited [blank_start]diffusion[blank_end] of oxygen, nutrients and [blank_start]substrates[blank_end] and less protection from [blank_start]predators[blank_end]. Water content and Oxygen diffusion affects [blank_start]occupancy[blank_end]. Pore size also affects the ability of microbes to [blank_start]move[blank_end] around and their ability to [blank_start]graze[blank_end] on soil [blank_start]microflora[blank_end] which then affects the transfer of bacterial [blank_start]production[blank_end] to other [blank_start]trophic[blank_end] levels. The interior if aggregates is [blank_start]anoxic[blank_end] and colonised by anaerobic bacteria while aerobic bacteria colonise the [blank_start]outside[blank_end] of aggregates. Microbe numbers [blank_start]decrease[blank_end] as depth of soil increases. Different groups of microbes are found at different [blank_start]depths[blank_end] of soil.

Rhizosphere Soil region under immediate influence of [blank_start]roots[blank_end]. Rhizosphere [blank_start]exudates[blank_end] include amino acids, organic acids, sugars, vitamins, [blank_start]mucilage[blank_end] and proteins and [blank_start]protect[blank_end] the rhizosphere and roots from pathogen [blank_start]attachment[blank_end]. The exudates also attract [blank_start]beneficial[blank_end] microbes, retains [blank_start]moisture[blank_end], obtains [blank_start]nutrients[blank_end] and stabilises [blank_start]aggregates[blank_end]. Rhizosphere has a high microbe population and is [blank_start]distinct[blank_end] from soil. Water [blank_start]uptake[blank_end] and root [blank_start]respiration[blank_end] affects soil [blank_start]oxygen[blank_end] levels and microbial [blank_start]respiration[blank_end]. Rhizodeposits are used as a [blank_start]carbon[blank_end] source by soil microbes. Release of [blank_start]ions[blank_end] my microbes modifies soil [blank_start]pH[blank_end], and secretion or uptake of [blank_start]chelates[blank_end] modifies nutrient availability

[blank_start]Carbon[blank_end] cycle is the driving force behind other nutrient cycles and [blank_start]microbes[blank_end] are critical to the cycle. [blank_start]Reservoirs[blank_end] of carbon can be physically or chemically [blank_start]separated[blank_end], but [blank_start]transformation[blank_end] or transfer between reservoirs can occur. Carbon reservoir in the [blank_start]atmosphere[blank_end] warms the planet due to fossil fuel and cement [blank_start]combustion[blank_end]. Terrestrial and ocean [blank_start]sinks[blank_end] mitigate some of the CO2 in the atmosphere. The temperature of Earth is much colder than the sun. The infra red radiation emitted by the sun has a [blank_start]short[blank_end] wavelength, and a [blank_start]longer[blank_end] wavelength when emitted by earth. Some [blank_start]gases[blank_end] interact with earth's wavelength and vibrate.

Silicate-Carbonate cycle: [blank_start]silicate[blank_end] rocks + soil [blank_start]CO2[blank_end] or organic acids form [blank_start]sedimentary[blank_end] rocks and [blank_start]saline[blank_end] oceans. [blank_start]Warms[blank_end] the plant and forms [blank_start]coal[blank_end] and fossil fuels. [blank_start]CO2[blank_end] is fixed by photosynthesis and the [blank_start]burial[blank_end] of organic matter Mineral weathering: [blank_start]Breakdown[blank_end] of rocks, soil or minerals Plants accelerate mineral weather process by secreting [blank_start]organic[blank_end] acids. Warm temperatures also promote weathering, [blank_start]soil[blank_end] formation and [blank_start]root[blank_end] growth if nit inhibited by [blank_start]water[blank_end] or nutrient availability. Burial of Organic Matter: During [blank_start]warm[blank_end] periods with [blank_start]high[blank_end] rainfall [blank_start]water[blank_end] accumulates in poorly [blank_start]drained[blank_end] areas creating [blank_start]hydromorphic[blank_end] soils dominated by [blank_start]aquatic[blank_end] vegetation. In [blank_start]suboxic[blank_end] conditions large amounts of organic [blank_start]detritus[blank_end] form which become [blank_start]buried[blank_end] under mineral sediments during [blank_start]colder[blank_end] periods when [blank_start]erosion[blank_end] occurs.

Photosynthesis [blank_start]fixes[blank_end] carbon and respiration [blank_start]releases[blank_end] carbon. Energy sourced from [blank_start]sun[blank_end] is transferred through the [blank_start]ecosystem[blank_end]. On land photosynthesis mainly by [blank_start]higher[blank_end] plants and by [blank_start]cyanobacteria[blank_end] and algae in the ocean. The ocean is largely unproductive for carbon fixation due to [blank_start]nutrient[blank_end] limitations, especially [blank_start]iron[blank_end]. Less than [blank_start]0.1[blank_end] of solar energy is used during photosynthesis. Oxic respiration: Sugar is the carbon and energy source and is oxidised by [blank_start]O2[blank_end] Anoxic respiration: Sugar is the carbon and energy source but is oxidised by [blank_start]NO3[blank_end]-,[blank_start]Mn[blank_end]4+, [blank_start]Fe[blank_end]3+ or [blank_start]SO4[blank_end]2- Methanogenesis: CO2 or CH3COOH oxidises H2 to form [blank_start]CH4[blank_end] under [blank_start]anaerobic[blank_end] conditions Photosynthesis: CO2 oxidised by O2 in presence of light to form [blank_start]sugar[blank_end] Methanotrophs: Bacteria and archaea that consume [blank_start]methane[blank_end] and live [blank_start]between[blank_end] oxic and anoxic environments where both [blank_start]oxygen[blank_end] and methane are present. Their contribution to the carbon cycle is [blank_start]small[blank_end] due to their [blank_start]restrictive[blank_end] environment.

Decomposition of organic [blank_start]detritus[blank_end] Most litter compounds are too [blank_start]large[blank_end] for microbes to digest, some are digested by [blank_start]exoenzymes[blank_end] released by microbes. Some biomass of detritus is [blank_start]protected[blank_end]. During decomposition Carbon is lost as [blank_start]CO2[blank_end] and organic matter becomes [blank_start]biomass[blank_end]. Not all carbon is lost, some is retained in the [blank_start]biomass[blank_end] and protected by both [blank_start]physical[blank_end] and chemical barriers.

Starch is a polymer of [blank_start]glucose[blank_end] and is hydrolysed by [blank_start]amylase[blank_end]. Most organisms can digest starch. Cellulose is a [blank_start]linear[blank_end] polymer of [blank_start]glucose[blank_end] and is [blank_start]high[blank_end] energy. It is surrounded by chains of [blank_start]hemicellulose[blank_end] and forms cell [blank_start]walls[blank_end]. Digestion by [blank_start]cellulase[blank_end] enzyme. Few organisms can digest cellulose, only those with [blank_start]bacterial[blank_end] symbionts. Hemicellulose is [blank_start]easier[blank_end] to digest. Microbes must use [blank_start]oxidation[blank_end] to produce free radicles to digest [blank_start]lignin[blank_end] to reach cellulose and hemicellulose. Oxidation releases [blank_start]CO2[blank_end]. [blank_start]Lignin[blank_end] surrounds cellulose and hemicellulose. It is a [blank_start]complex[blank_end] structure that is hard to [blank_start]decompose[blank_end]. Usually only decomposed by [blank_start]fungi[blank_end] that use free radicles. Brown rot and soft rot fungi digest the [blank_start]polysaccharides[blank_end] associated with lignin, but [blank_start]white[blank_end] rot fungi digests lignin completely and associated polysaccharides, [blank_start]cellulose[blank_end] not digested. Protein digested via [blank_start]protease[blank_end] enzymes and fat by [blank_start]lipase[blank_end]. Fat is harder to digest as it is [blank_start]hydrophobic[blank_end] so decomposition is [blank_start]slower[blank_end].

Physical protection of organic matter Pore spaces are not [blank_start]continuous[blank_end] so organic matter is not always accessible to [blank_start]decomposers[blank_end]. Degradation requires [blank_start]contact[blank_end] between the substrate and microbe. Pores which contain organic matter may have a [blank_start]neck[blank_end] size too small for microbes , such as [blank_start]clay[blank_end] soil, and microbes only occupy a [blank_start]small[blank_end] proportion of soil volume and are [blank_start]heterogeneously[blank_end] distributed. [blank_start]Charcoal[blank_end] very hard to digest as composed of benzene which is very high energy, requires [blank_start]enzyme[blank_end]. Interaction of organic compounds with [blank_start]minerals[blank_end] and ions decreases their [blank_start]decomposition[blank_end], such as [blank_start]allophane[blank_end] in volcanic soils, they have a [blank_start]high[blank_end] composition of organic matter. In clay soil, [blank_start]iron[blank_end] oxides precipitate on clay molecules [blank_start]increasing[blank_end] the surface area and organic matter attaches to the iron oxide [blank_start]precipitate[blank_end]. Soil [blank_start]high[blank_end] in compounds with a [blank_start]large[blank_end] surface area have more organic matter, and microbes require [blank_start]more[blank_end] energy to digest the organic matter. Organic matter is [blank_start]amphiphilic[blank_end]. The hydrophobic region faces the [blank_start]mineral[blank_end], and the exposed hydrophilic region attracts [blank_start]cations[blank_end], which attracts more of the mineral.

Properties of organic matter in soil Binds soil particles to form [blank_start]aggregates[blank_end], reduces [blank_start]erosion[blank_end], increases [blank_start]water[blank_end] holding capacity and increases [blank_start]tilth[blank_end]. Required for [blank_start]nutrient[blank_end] cycles, retains [blank_start]cations[blank_end], buffers soil [blank_start]pH[blank_end] and filters [blank_start]contaminants[blank_end]. Organic matter provides a source of [blank_start]carbon[blank_end] and energy to soil microbes, [blank_start]nutrients[blank_end] to plants, inactivates some [blank_start]pesticides[blank_end] and enhances degradation of pesticide [blank_start]residues[blank_end].