1.5 The origin of cells

Question 1

Abiogenesis

Answer 1

The theory that living cells arose from non-living matter

Question 2

Outline the process of abiogenesis

Answer 2

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 3

Miller-Urey experiment

Answer 3

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 4

Endosymbiont

Answer 4

a cell which lives inside another cell with mutual benefit

Question 5

Process of endosymbiosis

Answer 5

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

Question 6

Evidence for Endosymbiosis

Answer 6

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)

Question 7

Mnmemonic for endosymbiosis

Answer 7

MAD DR (mad doctor)

Question 8

Membranes

Answer 8

some organelles have double membranes

Question 9

Antibiotics

Answer 9

susceptible to antibiotics

Question 10

Division

Answer 10

reproduction occurs via a fission-like process

Question 11

DNA

Answer 11

has own DNA which is naked and circular

Question 12

Ribosomes

Answer 12

have ribosomes which are 70S in size