1.5 Origin of cells

Question 1

Definition of biogenesis

Answer 1

cells can only be produced from existing cells/ third part of the cell theory

Question 2

Long time ago people believe in _________, which is ________________

Answer 2

spontaneous generation / abiogenesis

where cells are produced from non living matter

Question 3

Who’s experiment proved abiogenesis wrong and explain the process and results of the experiment

Answer 3

Pasteur’s experiment

1. Broths placed in vessels (One is placed with swan neck ducts blocks all external dusts from entering ) and one is without swan neck duct
2. Broths were boiled to kill any microbes (Sterilisation)
3. Observe which vessels had growth of organisms

bacterial growth only occurred due to contamination of pre-existing cells

Question 4

How did the first cells arrive ?

Answer 4

1. simple organic molecules
2. develop into more complex polymers (possibly in deep sea vents)
3. Some polymers are RNA - self replication (inheritance)
4. These molecules packaged into membranes - naturally forming phospholipid bilayer - allowing molecules to have different conditions inside and outside of the cell to develop

Question 5

Why can’t abiogenesis occur in different temperatures?

Answer 5

• It has to have higher temps above 100 degree celsius
• reducing atmosphere (no oxygen)
• a lot of lightning (electrical discharge) catalyse reactions

These extreme temperatures are required for abiogenesis to occur.

Question 6

Explain why DNA came after RNA ?

Answer 6

• RNA can self replicate
• RNA acts as a catalyst
• RNA itself is basically an enzyme (replicate, pass on genes) IMPORTANT FOR INHERITANCE

Question 7

Describe the process that proves abiogenesis

Answer 7

1. Water boiled to reflect high temps on earth b4
2. vapour mixed with multiple gases to create reducing temperature
3. Mixture exposed to electrical discharge
4. Allowed to cool for 1 week
5. condensed mixture shows traces of simple organic molecules

Question 8

Explain the endosymbiotic theory

Answer 8

1. larger prokaryote engulfs smaller prokaryote by endocytosis (phagocytosis) forming a symbiotic relationship
2. Larger cells supply food to smaller one
   Smaller cells carry out process such as
   photosynthesis and aerobic respiration for larger
   cells
3. over generations these engulfed cell becomes an organelle (mitochondria and chloroplasts)

Question 9

Why did the mitochondria come before chloroplasts ?

Answer 9

All cells have mitochondria because they need to respire so therefore it was developed before chloroplasts. As chloroplasts are only in plant cells

Question 10

Name 5 evidence for endosymbiotic theory

Answer 10

1. Mitochondria and chloroplasts both have 70s ribosomes
2. They are roughly same size as prokaryote and they are double membrane
3. They divide by binary fission
4. Can transcribe DNA use mRNA to make proteins
5. They have their own genes and circular DNA molecules like prokaryotes

Question 11

How does the nucleus develop overtime ?

Answer 11

1. As prokaryote grows, it develop folds to maintain SA:V
2. These folds are then pinched off, forming nuclear membrane
3. nucleoid region is enclosed in the internal membrane and hence become the nucleus