Unit 4: Origins of life

Question 1

What is panspermia ?

Answer 1

Scientific hypothesis that suggests life has originated from microbial life such as bacteria or has come from meteorites

Question 2

What are the elements of primordial soup (4) ?

Answer 2

1) Early earth had a chemically reducing atmosphere
2) When exposed to energy, the atmosphere produced simple organic compounds
3) Compounds accumulated in a ‘soup’
4) By further transformation, more complex organic polymers developed

Question 3

What happened in the miller-urey experiment ?

Answer 3

• Stanley L.Miller simulated the conditions of early earth and tested for chemical origins of life
• He exposed gases to water vapour and an electrical spark
  RESULT- He found amino acid monomers

Question 4

What are hydrothermal vents (4) ?

Answer 4

• They are mid-oceanic rich systems that contain lots of heat and mineral rich water
• Low oxygen
• Porous rock acts as a cell membrane
• Bacteria runs a reverse Krebs cycle so generates compounds from CO2 and H2

Question 5

What system provides most evidence for the hypothesis ?

Answer 5

Hydrothermal vents

Question 6

What are the 3 domains of life ?

Answer 6

• Bacteria
• Eukaryota
• Archaea

Question 7

What is the RNA world hypothesis ?

Answer 7

That self replicating RNA molecules were precursors to current life, and catalyses chemical reactions

Question 8

What is the endosymbiotic hypothesis for the origin of mitochondria and chloroplasts ?

Answer 8

That ancestral prokaryotes engulfed an aerobic and photosynthetic prokaryote. This is how mitochondria and chloroplasts came to be in cells due to engulfing

Question 9

What is the evidence supporting the endosymbiotic theory ?

Answer 9

• Mitochondria and chloroplasts arise only from preexisting ones
• Antibiotics that block protein synthesis in bacteria work on organelles, not other parts of eukaryotes

Question 10

What does the mullers ratchet model show ?

Answer 10

The benefits of sexual reproduction

Question 11

What is the main benefit of sexual reproduction ?

Answer 11

Genetic material is recombined which prevents genetic loading

Question 12

What are the problems with asexual reproduction ?

Answer 12

• Over time genomes accumulate deleterious mutations that cannot be reversed
• This is known as genetic loading and this can cause populations to go extinct

Question 13

What is the animals hypothesis ?

Answer 13

That colonial protists gradually developed specialised cells and gastrulated

Question 14

What are choanoflagellates ?

Answer 14

Free living unicellular and colonial flagellated eukaryotes that are believed to be the closest living relative of animals (metazoans)

Question 15

What happened in the Cambrian explosion ?

Answer 15

• Predation appears for the first time
• Taxonomic and morphological diversity

Question 16

What was the precambrian earth referred to as ?

Answer 16

The ‘snowball earth’

Question 17

What are the 2 categories of things that may have triggered the Cambrian explosion ?

Answer 17

• Extrinsic or physical changes to environment
• Intrinsic or biological mechanism

Question 18

What are the extrinsic or physical triggers of the Cambrian explosion ?

Answer 18

• Breakup of supercontinent radian which produced more shallow water niches
• More oxygen and calcium ions in the water= better biomineralisation potential

Question 19

What are the intrinsic or biological triggers of the Cambrian explosion ?

Answer 19

• Genetic link between metazoans
• HOX genes are master controls which show differentiation
• Development of mutations in just one HOX gene can initiate a large morphological change in descendants