1.5 Origin of Cells

Question 1

what is the theory that living cells arose from non-living matter?

Answer 1

abiogenesis

Question 2

what is the process of abiogenesis theory? (4 step)

Answer 2

• there was non-living synthesis of simple organic molecules (from primordial inorganic molecules)
• these simple organic molecules became assembled into more complete polymers
• certain polymers formed the capacity to self-replicate (enabling inheritance)
• the molecules became packaged into membrane w/ an internal chemistry different from their surroundings (protobionts)

Question 3

what experiment demonstrated the non-living synthesis of simple organic molecules?

Answer 3

• the Miller-Urey experiment

Question 4

what was the process of Miller-Urey experiment? (6)

Answer 4

• Miller and Urey recreated the postulated pre-biotic death conditions using flasks and tubes
  1. water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions
  2. the vapour was mixed w/ a variety of gases (H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
  3. the mixture was the exposed to electrical discharge (stimulating the effects of lightening as an energy source for reactions)
  4. the mixture was allowed to cool and left for 1 week
  5. after this time, the condensed mixture was analysed and found to contain traced of simple organic molecules

Question 5

what conditions are required for the chemical processes that contributed to the initial formation of biological life?

Answer 5

• reducing atmosphere and high temperatures, electrical discharge to catalyse chemical reactions

Question 6

why can’t living cells arise independently by abiogenesis? (2)

Answer 6

the conditions do not commonly exist on modern Earth
- cells can only be formed by the division of pre-existing cells (biogenesis)

Question 7

what is biogenesis?

Answer 7

describes the principle that living things only arise from other living things by reproduction (not spontaneous generation)

Question 8

who and what experiment is attributed to have demonstrated the law of biogenesis?

Answer 8

• Louis Pasteur
• demonstrated that emergent bacterial growth in nutrient broths was due to contamination by pre-existing cells

Question 9

what is the biogenesis experiment? (4 steps)

Answer 9

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

Question 10

what is an endosymbiont?

Answer 10

a cell which lives inside another cell with mutual benefit

Question 11

where are eukaryotic cells believed to have come from? (3)

Answer 11

• evolved from early prokaryotes that were engulfed by phagocytosis
• the engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cells
• over generation, the engulfed cell lost some of its independent utility and became a supplemental organelle

Question 12

what are 2 organelles which are suggested to have arisen via endosymbiosis?

Answer 12

mitochondria and chloroplast

Question 13

what is evidence to support the extracellular origins of these organelles can be seen? (5)

Answer 13

Membranes - some organelle have double membranes (outer membrane may be vesicular in origin)
Antibiotics - susceptible to antibiotics (indicated organelles may have bacterial origins)
Division - reproduction occurs via a fission-like process
DNA - has own DNA is naked and circular (like prokaryotic DNA structure)
Ribosomes - have ribosomes which are 70S in size (identical to prokaryotic ribosome)