Ecosystems

A major goal in the study of ecosystems is to examine the production and utilization of energy. To assist in this goal, plants and animals are organized into groups called trophies levels:

Primary producers are autotrophs that convert sun energy into chemical energy. They include plats, photosynthetic protists, cyanobacteria, and chemosynthetic bacteria.
Detritivores are consumers that obtain their energy by consuming dead plants and animals (detritus). The smaller detritivores, called decomposers include fungi and bacteria. Other detritivores include nematodes, earthworms, insects, and scavengers such as crabs, vultures, and jackels.

Ecological pyramids are used to show the relationship between trophic levels. Horizontal bars or tiers are used to represent the relative sizes of trophic levels, each represented in terms of energy (also called productivity), biomass, or numbers of organisms.


Ecological efficiency describes the proportion of energy represented at one tropic level that is transferred to the next level. The relative sizes of tier in an energy pyramid indicate the ecological efficiency of the ecosystem. On average, the efficiency is only about 10%, that is, and 10% of the productivity of one trophic level is transferred to the next level. The remaining 90% is consumed by the individual metabolic activities of each plant or animal, or is transferred to detritivores when they die.

Because ecological efficency is so low. Nearly all domestic animals used for food or work are herbivores. Of a carnivore were raised for food or work, the energy requires to raise and sustain it would far exceed its value in food or work.

Biogeochemical Cycles

Biogeochemical cycles describe the flow of essential elements from the environment to living things and back to the environment. The following list outlines the major storage locations (reservoirs) for essential elements, the processes through which each element incorporates into terrestrial plants and animals (assimilation), and the processes through which each element returns to the environment (release).

Water Cycle (hydologic):


Reservoirs: oceans, air (as water vapor), ground water, glaciers. (Evaporation, wind, and precipitation move water from oceans to land)

Assimilation: plants absorb water from soil; animals drink water or eat other organisms (which are mostly water).

Release: plants transpire; animals and plants decompose

Carbon Cycle:

Carbon is required for the building of all organic compounds.

Reservoirs: atmosphere (as CO2), fossil fuels (coal, oil), peat, durable organic material (cellulose, for example).

Assimilation: plants use CO2 in photosynthesis; animals consume plants or other animals.

Release: plants and animals release CO2 through respiration and decomposition; CO2 is released when organic materials (such as wood and fossil fuels) are burned.


Nitrogen Cycle


Nitrogen is required for the manufacture of all amino acids and nucleic acids

Reservoirs: atmosphere (N2); soil (NH4+ of ammonium, NH3 or ammonia, NO2- or nitrite, or NO3- or nitrate)

Assimilation: plants absorb nitrogen either as NO3- of as NH4+; animals obtain nitrogen by eating plants or other animals. The stages in the assimilation of nitrogen are as followings:
• Nitrogen fixation: N2 to NH4+ by prokaryotes (in soil and root nodules); N2 to NO3- by lightening and UV radiation.
• Nitrification: NH4+ to NO2- and NO2- to NO3- by various nitrifying bacteria

Release: denitrifying bacteria convert NO3- back to N2 (denitrification); detrivorous bacteria convert organic compounds back to NO4+ (ammonification): animals excrete NH4+ (or NH3), urea, or uric acid.

Phosphorus Cycle

Phosphorus is required for the manufacture of ATP and all nucleic acids. Biogeochemical cycle of other minerals, such as calcium, such as calcium and magnesium, are similar to the phosphorus cycle.

Reservoirs: rocks. (erosion transfers phosphorus to water and soil; sediment and rocks that accumulate on ocean floors return to the surface as a result of uplifting by geological processes).

Assimilation: plants absorb inorganic PO43- (phosphate) form soils; animals obtain organic phosphorus when the eat plants or other animals.

Release: plants and animals release phosphorus when they compose; animals excrete phosphorus in their waste products
Chapter 16 Vocab

Telomerase: an enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.

Telomere: the tandemly repetitive DNA at the end of a eukaryotic chromosome's DNA molecule that protects the organism's genes from being eroded during successive rounds of replication.

Nuclease: an enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.

Helicase: an enzyme that untwists the double helix of DNA at the replication forks, separating the two strands and making then available as template strands.

Primase: an enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.

Primer: a short stretch of RNA nucleotides with a free 3' end, bound by complementary base pairing to the template strand, that is elongated with DNA nucleotides during DNA replication.
replication fork: a Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are growing.

Phage: a virus that infects bacteria

Bacteriaphage: a virus that infects bacteria

Transformation: (1) the conversion of a normal animal cell to a cancerous cell. (2) a change in genotype and phenotype due to the assimilation of external DNA by a cell.

Roots
telos: an end
semi: half
helic: a spiral
liga: bound or tied

Multiple Choice Questions

1. What are (is) the main process(es) that drive the water cycle?
a) evaporation of liquid water
b) condensation of water vapor
c) precipitation
d) transpiration
e) all of the above

2. Where do the largest amounts of phosphorus accumulate?
a) soils
b) oceans
c) sedimentary rocks of marine origin
d) organisms
e) phosphate absorbed by plants

3. The conversion of N2 by bacteria to forms that can be used to synthesize nitrogenous organic compounds is called:
a) nitrification
b) denitrification
c) ammonification
d) nitrogen fixation
e) osmosis