UNIT 1.5

Question 1

what is Abiogenesis ?

Answer 1

The theory that cells arose from non-living matter, broken down in to 4 key stages;
There was non-living synthesis of simple organic molecules (from primordial inorganic molecules)
These simple organic molecules became assembled into more complex polymers
Certain polymers formed the capacity to self-replicate (enabling inheritance)
These molecules became packaged into membranes with an internal chemistry different from their surroundings (protobionts)

Question 2

Outline the Miller-Urey experiment

Answer 2

Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions
The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions)
The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week
After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules

Question 3

What is Biogenesis

Answer 3

The theory that life can only come from life (At least at Earth’s current state);
-The chemical processes that contributed to the initial formation of biological life required specific conditions to proceed

• This included a reducing atmosphere and high temperatures (>100ºC) or electrical discharges to catalyse chemical reactions
• These conditions do not commonly exist on modern Earth and hence living cells cannot arise independently by abiogenesis
• Instead, cells can only be formed by the division of pre-existing cells (biogenesis)

Question 4

Outline Pasteur’s swan necked flask experiment

Answer 4

Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass
The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation)
Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside
From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur

Question 5

What is endosymbiosis (Endosymbiotic theory) and what is the supporting evidence ?

Answer 5

An endosymbiont is a cell which lives inside another cell with mutual benefit

Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis

The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis)

Over generations, the engulfed cell lost some of its independent utility and became a supplemental organelle

-Evidence for Endosymbiosis

Mitochondria and chloroplasts are both organelles suggested to have arisen via endosymbiosis

Evidence that supports the extracellular origins of these organelles can be seen by looking at certain key features:

Membranes (double membrane bound)
Antibiotics (susceptibility)
Division (mode of replication)
DNA (presence and structural composition)
Ribosomes (size)

Mnmemonic: MAD DR (mad doctor)