1. ORIGIN OF LIFE ON EARTH
Option D.1
IB Biology
Miss Werba

2. OPTION D - EVOLUTION D.1 ORIGIN OF LIFE ON EARTH D.2
SPECIES AND SPECIATION
D.3
HUMAN EVOLUTION
AHL D.4
THE HARDY–WEINBERG PRINCIPLE
AHL D.5
PHYLOGENY AND SYSTEMATICS
J WERBA – IB BIOLOGY 2

3. THINGS TO COVER
The conditions of pre-biotic Earth
Experiments of Miller and Urey
Hypothesis regarding first catalysts
Theory that regarding RNA and replication
Possible origin of membranes and prokaryotic cells
Endosymbiotic theory for the origin of eukaryotes
Awesome website for this topic:
J WERBA – IB BIOLOGY 3

4. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
There are 4 processes that were needed for the spontaneous generation of life on Earth:
non-living synthesis of simple organic molecules
assembly of organic molecules into polymers
origin of self-replicating molecules that made inheritance possible
packaging of self-replicating molecules into membranes
J WERBA – IB BIOLOGY 4

5. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
Non-living synthesis of simple organic molecules
The source of the molecules had to be abiotic.
Early Earth had to have all of the elements and compounds required.
Random – somehow able to combine themselves to make simple organic compounds.
Could have come from another source – eg. extra-terrestrial!
J WERBA – IB BIOLOGY 5

6. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
Assembly of simple organic molecules into polymers
There was very little oxygen in the atmosphere at the time, making oxidation difficult.
Resulted in a ‘reducing atmosphere’, which would have made formation of polymers more likely.
Random – somehow able to combine themselves to make larger polymers.
They are thought to have been formed on solid, mineral surfaces.
J WERBA – IB BIOLOGY 6

7. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
Origin of self-replicating molecules allowing inheritance
DNA can’t self-replicate. It needs protein enzymes (formed from it’s own instructions!).
Some RNA can self-replicate.
Utilised complementary base pairing.
These RNA molecules are called ribozymes and incorporate both the features required of life:
storage of information
the ability to act as catalysts
J WERBA – IB BIOLOGY 7

8. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
SOURCE: Purcell, D. (2009)
J WERBA – IB BIOLOGY 8

9. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
SOURCE: Purcell, D. (2009)
J WERBA – IB BIOLOGY 9

10. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
SOURCE: Purcell, D. (2009)
J WERBA – IB BIOLOGY 10

11. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
packaging of self-replicating molecules into membranes
Creates a bubble with a different internal chemistry from the surrounding environment.
Closed membrane vesicles (coacervates or protocells) can form spontaneously from lipids.
Random – somehow formed a “lipid- loop” around the RNA.
This is thought to have happened ~3.8 billion years ago.
J WERBA – IB BIOLOGY 11

12. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
SOURCE: Purcell, D. (2009)
J WERBA – IB BIOLOGY 12

13. THE SPONTANEOUS ORIGIN OF LIFE Command term = DESCRIBE
SOURCE: Purcell, D. (2009)
J WERBA – IB BIOLOGY 13

14. THE MILLER-UREY EXPERIMENT Command term = OUTLINE
In 1953, Stanley Miller and Harold Urey worked on trying to confirm some of these ideas regarding pre-biotic Earth.
Set up an apparatus to simulate conditions of early Earth.
J WERBA – IB BIOLOGY 14

15. THE MILLER-UREY EXPERIMENT Command term = OUTLINE
The atmosphere on Earth at this time probably contained a variety of inorganic molecules:
Hydrogen
Nitrogen
Water vapour
Methane
Ammonia
No oxygen gas until after plants formed and started photosynthesising.
J WERBA – IB BIOLOGY 15

16. THE MILLER-UREY EXPERIMENT Command term = OUTLINE
The conditions on pre-biotic Earth at this time included:
A reducing atmosphere (resulting from the lack of oxygen)
Frequent electrical storms
High temperatures (due to greenhouse gases)
High radiation levels (no ozone so was extreme)
Volcanic activity
Meteorite bombardment
J WERBA – IB BIOLOGY 16

17. THE MILLER-UREY EXPERIMENT Command term = OUTLINE
Miller and Urey recreated the conditions of pre-biotic Earth in a closed system:
High temperatures/volcanic activity – a flask of water was boiled to generate water vapour
Reducing atmosphere –a mixture of ammonia, methane and hydrogen was introduced
Electrical storms – electric sparks were used to simulate lightning
The mixture was then allowed to cool.
After one week, they found some simple amino acids in the mixture (13 of 20 essential Aas) and 15% of the carbon present were now in organic compounds.
J WERBA – IB BIOLOGY 17

19. THE MILLER-UREY EXPERIMENT Command term = OUTLINE
Based on these findings, it was concluded that under the hypothesised conditions of pre-biotic Earth, organic molecules could be formed.
J WERBA – IB BIOLOGY 19

20. PANSPERMIA Command term = STATE
Comets may have delivered organic compounds to Earth.
Comets contain a variety of organic compounds.
Heavy bombardment about 4,000 million years ago may have delivered both organic compounds and water to the early Earth.
The hypothesis that life on Earth originated from material delivered by a comet is called Panspermia.
J WERBA – IB BIOLOGY 20

21. SYNTHESIS OF ORGANIC COMPOUNDS Command term = DISCUSS
Organic synthesis requires the presence of inorganic molecules and an energy source to combine them into organic forms
There are several possible locations where conditions would have allowed the synthesis of organic compounds.
Examples include:
deep-sea hydrothermal vents
volcanoes
extra-terrestrial locations
J WERBA – IB BIOLOGY 21

22. SYNTHESIS OF ORGANIC COMPOUNDS Command term = DISCUSS
Deep-sea hydrothermal vents
Conditions in the ocean were not ideal for the formation of long polymers.
This is because they would have hydrolysed in the water as they formed.
Deep-sea hydrothermal vents allow superheated steam to escape from within the Earth’s crust.
They also release sulfides into the water which crystallise in the area around the vent.
This may be a suitable environment for the formation of more complex biological compounds.
J WERBA – IB BIOLOGY 22

24. SYNTHESIS OF ORGANIC COMPOUNDS Command term = DISCUSS
Volcanoes and geysers
Volcanoes and geysers may also have provided suitable locations for the formation of biological compounds
They could provide sufficient thermal energy either on land or under the seabed.
Gases released from hot lava contain higher than average levels of fixed nitrogen:
eg. ammonia (NH4) is able to form from nitrogen gas
J WERBA – IB BIOLOGY 24

25. SYNTHESIS OF ORGANIC COMPOUNDS Command term = DISCUSS
Extra-terrestrial locations
Other planets (eg. Mars) may have been subjected to appropriate conditions for the formation of organic compounds.
These could have been transferred via meteorites.
Meteorites of Mars origin have been found in Antarctica.
There is no evidence that life has been transferred this way, and it still doesn’t explain how life formed!
J WERBA – IB BIOLOGY 25

26. PROPERTIES OF RNA Command term = OUTLINE
RNA can store, transmit and replicate genetic information.
RNA has two specific properties that would have allowed it to play a role in the origin of life:
It is self-replicating
It has catalytic properties
J WERBA – IB BIOLOGY 26

27. PROPERTIES OF RNA Command term = OUTLINE
As previously mentioned, ribozymes are RNA molecules that can catalyse reactions.
They can polymerise nucleotides using ATP.
Short sequences of RNA have been able to duplicate other molecules of RNA accurately.
Modern cells use ribozymes to remove introns from mRNA and help synthesise new RNA molecules.
In ribosomes, rRNA is found in the catalytic site and plays a role in peptide bond formation.
J WERBA – IB BIOLOGY 27

28. PROPERTIES OF RNA Command term = OUTLINE
J WERBA – IB BIOLOGY 28

29. PROTOBIONTS Command term = STATE
Living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings.
Proto = first or precursor
Coacervates are “droplets” or “bubbles” of polymers.
Coacervates can form around molecules, creating a different internal environment from their surrounds.
They can divide into smaller droplets when their SA:vol ratio limits their size.
J WERBA – IB BIOLOGY 29

30. PROTOBIONTS Command term = STATE
Living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings.
Protobionts may have arisen from coacervates.
Coacervates may contain RNA.
As RNA is self-replicating, it could have started synthesising proteins.
These proteins may have included the enzymes needed to control binary fission.
J WERBA – IB BIOLOGY 30

31. PROTOBIONTS Command term = STATE
Living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings.
Protobionts may also have arisen from microspheres.
Microspheres form by heating amino acids.
They divide like coacervates and can catalyse some reactions.
J WERBA – IB BIOLOGY 31

32. CONTRIBUTION OF PROKARYOTES Command term = OUTLINE
Primordial Earth had a reducing atmosphere, meaning that it contained very low levels of oxygen gas.
After about ~2 billion years of prokaryotic life, a form of chlorophyll evolved in prokaryotes (forming cyanobacteria).
This allowed photosynthesis to occur, creating oxygen gas as a by-product via the photolysis of water.
J WERBA – IB BIOLOGY 32

33. CONTRIBUTION OF PROKARYOTES Command term = OUTLINE
J WERBA – IB BIOLOGY 33

34. CONTRIBUTION OF PROKARYOTES Command term = OUTLINE
The increase in oxygen in the atmosphere lead to: 
The breakdown of chemicals in the atmosphere and oceans to produce oxidised compounds (eg. CO2)
The evolution of organisms capable of breaking down oxygen-rich oxidising agents
The formation of an ozone layer which restricted UV radiation (stopping synthesis of more inorganic molecules and allowing a wider range of life to proliferate)
J WERBA – IB BIOLOGY 34

35. THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
Grypania is ~2mm in diameter, so it is too big to be a prokaryotic cell.
SOURCE: McFadden, G. (2009)
J WERBA – IB BIOLOGY 35

36. Tappania is definitely too big and complicated to be prokaryotic.
THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
Tappania is definitely too big and complicated to be prokaryotic.
SOURCE: McFadden, G. (2009)
J WERBA – IB BIOLOGY 36

37. THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
Bangiomorpha had 3D structure! Definitely too complicated to be prokaryotic!
SOURCE: McFadden, G. (2009)
J WERBA – IB BIOLOGY 37

38. THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
The oldest fossils of eukaryotic cells have been found to be ~1.5 billion years old.
The endosymbiotic theory from Lyn Margulis (1967) tries to explain the origin of eukaryotes.
Endosymbiosis: the condition in which one organism lives inside the cell of another organism
Both cells benefit from this - the cells no longer can live separately from each other
J WERBA – IB BIOLOGY 38

40. THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
The theory stipulates that chloroplasts and mitochondria were once free-living prokaryotes:
Mitochondria  aerobic bacteria
Chloroplasts  photosynthetic bacteria
These cells were engulfed by larger prokaryotes (endocytosis).
J WERBA – IB BIOLOGY 40

41. THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
Evidence to support the theory includes:
Both mitochondria and chloroplasts contain their own DNA (naked and circular like bacterial DNA).
They have a double membrane (own of their own and one from being engulfed).
They have 70S ribosomes.
They are the same size as bacterial cells.
They can replicate on their own in a process similar to binary fission.
Chloroplasts are similar in structure to cyanobacteria.
J WERBA – IB BIOLOGY 41

42. THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
The four eukaryotic kingdoms are:
Protoctista
Fungi
Plantae
Animalia
Eukaryotic cells have some advantages over prokaryotic cells so the early eukaryotes survived and proliferated
Hence the wide diversity of species we know today!
J WERBA – IB BIOLOGY 42

43. THE ENDOSYMBIOTIC THEORY Command term = DISCUSS
TOK:  marks in the newer markschemes for TOK links
As with other theories that aim to explain the evolution of life on Earth, we can obtain evidence for a theory and we can assess the strength of the evidence.
However, can we ever be sure that the theory explains what actually happened in the past?
For something to be a scientific theory, we must also be able to test whether it is false.
Can we do this if the theory relates to a past event? If they cannot be falsified, is it enough if they allow us to make predictions?
This theory cannot be falsified. And it only explains some aspects of eukaryotic structure/behaviour.
J WERBA – IB BIOLOGY 43

44. Sample questions
Q1 (8 min)
The spontaneous origin of life on Earth is thought to have involved the non-living synthesis of simple organic molecules.
a) List two other processes needed for the spontaneous origin of life. [2]
b) Discuss possible locations where conditions would have allowed the synthesis of organic compounds. [2]
c) Outline the role of prokaryotes in the development of an oxygen-rich atmosphere on the Earth. [2]
J WERBA – IB BIOLOGY 44

45. Sample questions
Q2 (9 min)
Discuss the endosymbiotic theory for the origin of eukaryotes. [6]
J WERBA – IB BIOLOGY 45

46. Sample questions A1
a) simple molecules must polymerize/assemble into polymers;
formation of self-replicating molecules;
simple molecules must become isolated from the surroundings/enclosed
in membranes; 2 max
b) in water as organic reactions are aqueous;
conditions near geothermal vents/volcanic pools allow high reaction rates;
evaporation of water allows organic (precursor) molecules to become more concentrated;
high temperatures not desirable as organic molecules become unstable;
clay minerals may act as catalysts / clay forms a matrix for monomers to attach; 2 max
c) early atmosphere was oxygen free;
some prokaryotes could carry out chemosynthesis;
cyanobacteria developed the ability to photosynthesize;
used water as hydrogen source so released oxygen;
oxygen began to accumulate in the atmosphere; more photosynthesis than respiration; 2 max
J WERBA – IB BIOLOGY 46

47. Sample questions Q2 eukaryotes evolved from prokaryotes;
mitochondria/chloroplasts evolved from prokaryotic cells;
taken in by larger (heterotrophic) cell by endocytosis;
theory supported by characteristics of chloroplasts/mitochondria;
[2 max] for mitochondria/chloroplast characteristics:
they have naked DNA;
they divide;
they have 70S ribosomes/synthezise own proteins;
they have double membranes;
some structures within them are similar to structures in prokaryotes;
TOK link: theory cannot be falsified as it predicts something occurring in the past;
theory does not explain the origins of other structures like flagella or processes like meiosis;
weaker evidence that cilia/flagella evolved from attached bacteria; [6]
J WERBA – IB BIOLOGY 47