Oxygen Flashcards
What are the key features that distinguish Type I and Type II photosynthetic reaction centres?
Type I have a protein attached to their negative side that pumps electrons into the cell. Type II have a protein attached to their positive side which feeds electrons in from outside of the cell.
What are Cyanobacteria?
“Blue-green algae” which contain Type I and II reaction centres
Explain how Type I and II reaction centres came together in cyanobacteria.
Lateral gene transfer allowed for genetic material to be transferred between bacterial easily eventually leading to the presence of both reaction centres.
Why did the presence of both types of reaction centre allow cyanobacteria to use water as an electron donor?
Both centres eventually coupled and started to work together providing more energy than before, this allowed more things to be oxidised.
What evidence is there for early oxygen production and cyanobacteria?
Stromatolites (fossilised microbial mats) and bands of iron oxides within rock.
How did oxygen cause the worlds first ice age?
The Huronian ice age was caused by oxygen reacting with methane in the early atmosphere. This produce carbon dioxide a less powerful greenhouse gas, this couple with weaker solar radiation caused mass cooling.
What other chemical reaction took place due to oxygen and also contributed to the mass extinction event?
Oxygen reacted with reduced iron to form oxidised iron and superoxide (a free radical) this then reacts with itself forming hydrogen peroxide (bleach). Furthermore, hydrogen peroxide reacted with reduced iron to produce hydroxyl radicals which are the most reactive molecule (react with DNA…=Bad)
Explain one positive of increased oxygen levels
Oxygen reacted with UV from the sun to form ozone. This blocks incoming UV rays and is fundamental to supporting life’s movement into land.
Explain why oxygenation of the atmosphere allowed the evolution of large cells.
Oxygen allowed for aerobic respiration which is much more efficient than anaerobic respiration (18 times more), allowing cells to become larger.
Explain the evolution of eukaryotes.
As cells got larger phagocytosis could occur (eating other cells). Eukaryotes were the first heterotrophs and it is believed that the development of organelles such as mitochondria occurred due to endosymbiotic relationships between early Eukaryotes and engulfed Prokaryotes. (evidence for this is the double membrane of mitochondria)
What key features characterise the Eukaryotic cell?
A nucleus, organelles, size and complexity, asexual and sexual reproduction (meiosis and mitosis) and DNA structure (chromosomes).
What is the significance of the development of sexual reproduction (meiosis)
It allows for efficient “shuffling” of genes.
