IB Biology Option D SL&HL
Evolution
What processes were needed for
life to evolve spontaniously?
• Synthesis of organic molecules (without
the presence of living things)
• Polymerisation of the simple organic
molecules
• Appearance of Self-replicating molecules
(for inheritance)
• Membranes to package these molecules
so they were different from their
surroundings.
Experiments of Miller & Urey
After a week;
• 15% of the C was in
organic molecules
• 13 of the 20 amino acids
were detected
• Adenine nucleotides also
present
Panspermia
• The hypothesis that life on earth originated in
the introduction of complex organic molecules,
or bacteria in comets.
• Recent evidence suggests that Comets may
have brought complex organic compounds (or
even bacteria) to earth.
• 4000 million years ago a comet shower could
have brought organic molecules to earth.
• Hydrocarbons, and peptides are thought to exist
on some comets.
Possible locations for synthesis of
complex organic compounds.
• Black smokers
(hydrothermal vents on ocean floor)
• Volcanoes
(they did fix Nitrogen)
• Extraterrestrial (eg on Mars)
Two properties of RNA
•
•
•
•
A molecule capable of replication
As rybozymes RNA can act as an enzyme
Ribosomes are rybozymes
RNA molecules are capable of variation
Protobionts preceeded cells
• A sort of boundary (not phospholipids) preceeded
plasma membranes.
• Coacervate droplets can spontaniously form.
Microspheres also show similar properties.
• Experiments with coacervate droplets have shown
membrane like properties (except reproduction)
• Protobionts could have been coacervate droplets and
RNA polynucleotides
• Protobionts could have made proteins and used
enzymes (or rybozymes) to control some sort of binary
fission.
Prokaryotes helped to create an
oxygen rich environment
• UV radiation & water vapour  oxygen
• Oxygen can react with water to make H2O2
that can degrade lipids and nucleic acids
(like RNA).
• So any organism containing protective
catalase enzyme will have an advantage.
The Oxygen Catastrophe
• Around 2 billion years ago there was an
explosive rise in oxygen levels.
• Probably caused by cyanobacteria doing a
simple form of photosynthesis
• This would have created an oxone layer and
prevented the formation of new organic
molecules from the primeval soup
• The oxygen would have oxidised any organic
molecules not protected in living things????
Endosymbiosis
(endosymbiotic theory)