Lecture 19 Flashcards
Tree of Life
By examining the genome of cells, biologists have established that there are two basic forms to all life:
- procaryotes
- eukaryotes
Procaryotes
Smallest, least complex cellular organisms. Distinguished from eukaryotes by their lack of a nuclear membrane and any internal organelles.
Why are procaryotes central to biosphere?
Procaryotes are central to biosphere because:
- of the diversity of their metabolic processes
- they comprise about 90% of biosphere
- the ability of archaea to live in extreme environments
- symbiotic relationships with many eukaryotes
- role in evolution
- come in 3 basic shapes (spheres, rods, and spirals)
Autotrophic
a metabolic process that synthesizes living protoplasm from inorganic matter in the environment (requires non-catabolic energy input).
What are the types of autotrophic metabolism?
Lithotrophic (chemoautotrophic) and phototrophic.
Heterotrophic
Metabolic process that synthesizes living protoplasm from organic matter in the environment (humans). Uses catabolism.
Catabolism
refers to the breakdown of organic material to release energy.
Lithotrophic (chemoautotroph)
Uses inorganic compounds as their energy source. Lithotrophs can be facultative or obligate lithotrophs. Facultative lithotrophs can use heterotrophy when organic material is present.
Methane bacteria
actually archaea (or archybacteria). They are obligate anaerobes. Only can exist in the absence of O2.
Hydrogen Bacteria
convert H2 to H2O using special enzyme (hydrogenase)
Sulfur Oxidizing Bacteria
converts H2S to SO4 (Using O2). These organisms along with another group of lithotrophs (iron bacteria) are responsible for acid mine drainage.
Nitrifying Bacteria
Convert NH3 to NO3 (Using O2). Important part of nitrogen cycle.
Photoautotrophs
Use sunlight as their energy source. These must have a “photon absorber” such as chlorophyll.
What are the 2 types of photoautotrophs?
Aerobic photosynthesis and anaerobic photosynthesis.
Aerobic Photosynthesis
These include green plants and algae (eukaryotes) and cyanobacteria (also known as blue-green bacteria). Cyanobacteria also fix nitrogen.
Anaerobic Photosynthesis
purple and green bacteria.
Heterotrophs
In heterotrophy oxygen atoms are used to convert organic C to CO2 and in the process release energy. Examples include fermenting bacteria and some eukaryotes (yeast), sulfate-reducing bacteria, denitrifying bacteria, and respirers.
Carbon Cycle
Photosynthesis, respiration, and biodegration.
Biodegredation
Depolymerization by enzymes, fermentation, decay of monomers via respiration
Nitrogen Cycle
Critical metabolic process in the geochemical cycle. Involves photosynthesis, biodegredation, nitrification, denitrification, and nitrogen fixation.
Sulfur Cycle
Important metabolic process. Includes aerobic photosynthesis, anaerobic photosynthesis, and degredation (sulfate reduction).
Geologic Time
Eons->Eras->Periods->Epochs
Relative Dating
Principal of superposition in stratigraphy.
Absolute Dating
Radiometric dating
The Hadean
~1billion years ago. Evolution of basic physical environment. The Earth formed: Solid Earth must have been molted and differentiated. The initial atmosphere must have been stripped away. The secondary atmosphere (and ocean) arose from degassing of volatile material from earth’s interior or by cometary bombardment.
The Archean
Procaryotes appear. Fossil record indicate 1st appearance of life ~3.5b years ago (evidence: microfossils and stromatolites)
Stromatolites
Layered sedimentary mats of limestone presently laid down by cyanobacteria
How did life originate? (hypothesis)
from Oparin in 1924. Said that the energy from solar UV light of lightning discharge caused the formation of organic molecules from reduced atmosphere gases. These organic molecules eventually formed amino acids and then protein of increasing complexity, which eventually became self-replicating.
Miller and Urey
in 1953 proved that the HCN and eventually amino acids can be generated by electrical discharge in highly reducing atmospheres.
Problems with Oparin/Miller-Urey Hypothesis
pre-biotic atmosphere probably not high reducing but only moderately reducing. Experiments produced amino acids but not self-replicating systems.
Rise of Photosynthesizers in the Archean.
Geologic record indivates the appearance of photosynthesizers about 2-3.5 bya. This is explained by the BIF.
Banded Iron Formations (BIF)
BIF’s are alternating layers of chert (SiO2) and iron. The iron is hematite and magnetite. They are not formed today. In order to form:
- Reduced iron must have been present so the iron can dissolve and be transported to regions of sediment formation.
- This reduced iron must have been oxidized to form ferric ion and the oxidize iron sediments.
Redbeds
Redbeds are sandy sediments containing hematite. The oldest of these deposits is ~2byo. They formed when BIF stopped forming. This implies that O2 began to accumulate in the atmosphere (and ocean) in significant quantities so that there was a continuous deposition of oxidized iron.
The Proterozoic and Beyond
Eukaryotes appear and with the appearance an explosion in biodiversity. 1.4bya: some time in the middle proterzoic the fossil record indicates the first appearance of eukaryotes. 700mya: 1st multi-celled animals.
Has oxygen levels varies much over geologic time?
The fire window suggests that O2 has remained constant over the past ~360 my.
Terms of Biogeochemical cycles
Reservoir amount, flux, and residence time.
Steady State
A reservoir is in steady state if the rate of the inflow equals the rate of outflow. The reservoir will not change.
