1.5 - Tushar

Question 1

How are cells formed

Answer 1

By the division of pre-existing cells (biogenesis)

Question 2

What was believed before in the formation of cells

Answer 2

Spontaneous generation - living organisms arose from non-living matter

Question 3

What was pasteur’s experiment

Answer 3

1) broths stored in vessels with swan neck which did not allow external dust to enter
2) Broths boiled to kill all micro organisms
3) Growth only occurs if the flask was open

shows that spontaneous growth is not real, bacterial growth was only due to contamination of pre-existing cells

Question 4

How did the first cell arrive

Answer 4

abiogenesis (living thing made from non-living matter)

1) non-living synthesis of simple organic molecules
2) assembly of these simple organic molecules to more complex polymers (possibly in deep sea vents)
3) certain polymers formed the capacity to self-replicate (enabling inheritance)
4) molecules were packed into membranes (phospholipids naturally assembled into bilayers), this allowed the molecules to have different internal chemistry from surroundings

Question 5

What genetic material came first

Answer 5

RNA

• it could self-replicate
• could act as a catalyst (enzyme) (enzymes are needed for self-replication)

Question 6

Proof that everything arose from 1 cell

Answer 6

64 codons in the genetic code, same meaning in nearly all organisms

Question 7

How was the atmosphere in Earth before

Answer 7

reducing atmosphere (less oxygen). High temperatures and a lot of electrical discharges (lightning)

the atmosphere is not like this now so only biogenesis can occur now

Question 8

What is the miller-urey experiment

Answer 8

Water boiled to reflect high temp
Vapour mixed with ammonia, hydrogen, methane to recreate reducing atmosphere
Mixture exposed to electrical discharge
Condensed mixture had traces of simple organic molecules

Question 9

Endosymbiotic theory

Answer 9

How mitochondria and chloroplast came, they were once independent prokaryotes

• eukaryotes were formed due to endosymbiosis
• host cells (larger prokaryotes) engulfed smaller prokaryotes (endocytosis)
• then these prokaryotes formed a symbiotic relationship
• smaller cells supplied with food
• smaller cell carried out processes (mitochondria/photosynthesis) for the larger cell
• Over generations, the smaller cell became an organelle

Question 10

Which came first, mitochondria or chloroplast

Answer 10

Mitochondria

as all cells have mitochondria but not all have chloroplast

Question 11

Evidence for endosymbiotic theory

Answer 11

• mitochondria and chloroplasts have their own genes on a circular DNA molecule, like prokaryotes
• mitochondria and chloroplasts have 70s ribosomes, like prokaryotes
• mitochondria and chloroplasts are roughly the same size as prokaryotes
• Mitochondria and chloroplast transcribe their own DNA and use the mRNA to make proteins, like prokaryotes
• mitochondria and chloroplast divide by fission like processes, like prokaryotes
• double membrane formed when engulfed

Question 12

How was nucleus formed

Answer 12

• prokaryotes grows and develops folds in its membrane to maintain efficient SA:V
• infolds are pinched off forming an internal membrane
• nucleoid region is enclosed in the internal membrane and hence nucleus is formed

Question 13

Discussions to the endosymbiotic theory

Answer 13

• the theory cant be falsified as it predicts something happening in the past
• the theory does not explain the origins of cilia and flagella and other organelles