1. D1 Origin of Life on Earth
IB Biology
Option D
D1 Origin of Life on Earth
(Timeline of Origin of Life)

2. D.1.1 Describe four processes needed for the
spontaneous origin of life on Earth
The non-living synthesis of simple organic molecules:
Obviously if nothing was alive yet, then the source of these molecules had to be abiotic
We can presume that the early Earth had all of the base elements and compounds required
They were somehow combined to make simple organic compounds
Maybe the organic compounds
were generated here, maybe they
were extra-terrestrial!

3. D.1.1 Describe four processes needed for the
spontaneous origin of life on Earth
The assembly of these molecules into polymers:
In order to make the larger molecules necessary for life, the simple organic compounds would have to polymerize
The origin of self-replicating molecules made inheritance possible:
DNA can’t self replicate, it needs protein enzymes
However some RNA can self-replicate - it can catalyze
the formation of copies of itself.
They are called Ribozymes and are the basis of the
RNA World Hypothesis

4. D.1.1 Describe four processes needed for the
spontaneous origin of life on Earth
4) The packaging of these molecules into membranes
with internal chemistry different from their surroundings:
The formation of closed membranes an important step
Closed membrane vesicles can form spontaneously from lipids
This allowed differentiation between the internal and external environments
(On formation of protocell)

5. Can you identify these molecules?
D.1.2 Outline the experiments of Miller and Urey
into the origin of organic compounds
Earth’s atmosphere was ‘reducing’ in the early days. It did not contain oxygen gas until after plants started photosynthesising
Can you identify these molecules?

6. D.1.2 Outline the experiments of Miller and Urey into
the origin of organic compounds
Earth’s atmosphere was ‘reducing’ in the early days. It did not contain oxygen gas until after plants started photosynthesizing
The atmosphere contained:
Hydrogen
Nitrogen
Water vapour
Methane
Ammonia
Hydrogen sulfide
The gases came from abundant volcanic activity

7. D.1.2 Outline the experiments of Miller and Urey into
the origin of organic compounds
These monomers mixed in the ‘primordial soup’, shallow oceans
with chemicals, where it is thought that they reacted to form
biological molecules
Miller and Urey tried to recreate these conditions in the lab in 1953
They were trying to demonstrate ‘chemical evolution’, the formation of more complex molecules from simpler stock in the primordial soup
They combined the molecules from the previous page in a closed glass vessel (simulated atmosphere), they heated the water (simulated volcanic activity) and sparked electricity through the gases (simulated lightning)

8. D.1.2 Outline the experiments of Miller and Urey into
the origin of organic compounds

9. D.1.2 Outline the experiments of Miller and Urey into
the origin of organic compounds

10. D.1.2 Outline the experiments of Miller and Urey into
the origin of organic compounds
After a week they found:
Thirteen of the twenty naturally occurring amino acids
Around 15% of the carbon was now in organic compounds

11. Space is so empty, yet full of the potential for life
D State that comets may have delivered
organic compounds to Earth
Panspermia is the hypothesis that life on Earth originated from material delivered by a comet, either in the form of amino acids or as hardy bacteria
Space is so empty, yet full of the potential for life
Existing bacteria and archaebacteria have been found in odd and extreme environments on Earth:
In hot springs, kilometres deep in the crust and even embedded in ice cores from deep inside Antarctica
It is feasible that they could survive on or in a comet

12. D.1.3 State that comets may have delivered
organic compounds to Earth
Cosmic radiation could provide the energy for reactions that lead to the formation of complex organic molecules
Analysis of the spectra of light coming from the comets reveals the presence of hydrocarbons, amino acids and peptides
The bombardment of Earth by comets 4 billion years ago could have ‘kick started’ chemical evolution

13. D.1.3 State that comets may have delivered
organic compounds to Earth
The hypothesis that life came an extraterrestrial source:
As previously mentioned, organic molecules are out there
Mars is smaller than Earth and therefore cooled down more quickly, life could have begun there while Earth was still scorching
Meteorites and comets impacting on mars could have thrown up debris with early life attached, this could then have crashed on Earth. Meteorites of Mars origin have been found in Antarctica

14. D.1.3 State that comets may have delivered
organic compounds to Earth
The hypothesis that life came an extraterrestrial source:
There is no evidence that life has been transferred in this way. Every now and then there is a news story about “Fossils found in Mars meteorite” but so far this has not been confirmed
The extraterrestrial hypothesis still doesn’t address how life formed, just how it could move around the galaxy

15. D Discuss possible locations where conditions would have allowed the synthesis of organic compounds
Locations needed to be a reducing (electron adding) environment to encourage compound formation
communities around
deep-sea hydrothermal vents
volcanoes
extraterrestrial locations (carried to earth on a comet).

16. RNA shows enzymatic (catalytic) properties – called ribozymes
D.1.5 Outline Two properties of RNA that would have
allowed it to play a role in the origin of life
RNAs can store, transmit and replicate genetic Information
RNA is composed of a single helix. The bases are exposed and ready to combine with a complement, making replication simpler
RNA was probably the first hereditary molecule having the ability to copy itself
RNA shows enzymatic (catalytic) properties – called ribozymes
Ribozyme: an RNA molecule that
catalyzes a chemical reaction

17. D.1.5 Outline Two properties of RNA that would have
allowed it to play a role in the origin of life
Once RNA became enclosed in membranes, these protobionts would have a form of heredity.
These protobionts may be selected
for survival.
RNA may have directed the sequencing of
amino acids to form primitive enzymes.

18. Origin of cell formation
D.1.6 State that living cells may have been preceded
by protobionts, with an internal chemical
environment different from their surroundings
Origin of cell formation
 Began as molecular aggregates
 Separate inside from outside
 Divide often (binary fission)
 Grow larger in size
 Maintain a level of homeostasis internally
 Produce electrical potential across surfaces
 Absorbs materials from the surface (selective
permeability)
 Catalytic actvity
Bubbles… Tiny bubbles…

19. Protobionts = Aggregation of abiotically produced
D.1.6 State that living cells may have been preceded
by protobionts, with an internal chemical
environment different from their surroundings
Protobionts = Aggregation of abiotically produced
molecules in droplets
- Maintain an internal environment different from
their surroundings.
- Exhibit some properties associated with life:
metabolism and reproduction
- May have arisen from coacervates, microspheres, or
liposomes

20. of polymeric molecules
D.1.6 State that living cells may have been preceded
by protobionts, with an internal chemical
environment different from their surroundings
Coacervate = droplets
of polymeric molecules
Colloidal suspension of macromolecules
A water film acts as a barrier like a cell membrane
Grows in size
When large enough, it breaks down into small globules with the same
traits as that of the “parent”

21. Microsphere = polypeptides with a semipermeable protein membrane
D.1.6 State that living cells may have been preceded
by protobionts, with an internal chemical
environment different from their surroundings
Microsphere = polypeptides with a semipermeable protein membrane
formed by adding water to polypeptides
show an electrical potential - may absorb materials
from the surrounding environment
membranes are made of phospholipid bilayers with proteins
may give clues to the evolution of the
cell membrane
undergo shrinking and swelling due to
osmosis

22. D.1.6 State that living cells may have been preceded
by protobionts, with an internal chemical
environment different from their surroundings
Liposome = form spontaneously when the organic molecules includes lipids
Form lipid bilayer membrane
Grow by engulfing other liposomes and may split to form two

23. How Polymerization could Occur?
D.1.6 State that living cells may have been preceded
by protobionts, with an internal chemical
environment different from their surroundings
How Polymerization could Occur?
Clay was thought to be a possible site for polymerization
(rather than primordial soup in the sea)
Binds well to organic molecules
Contains Zinc, iron, nickel, etc serving as a catalyst
Has been shown to occur experimentally:
dry clay...heat it amino acids can spontaneously join & form polypeptides!! ...can possibly form microspheres

24. Prokaryotes dominated life on Earth from 3.5–2.0 bya
D.1.7 Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere
Prokaryotes dominated life on Earth from 3.5–2.0 bya
3.5 billion year old fossil of bacteria
modern bacteria
chains of one-celled cyanobacteria

25.  Stromatolites offer more fossil evidence
D.1.7 Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere
Lynn Margulis
 The first cells were prokaryotic
 Stromatolites offer more fossil evidence
– rocklike columns composed of many minute layers of
prokaryotic cells (usually cyanobacteria)
 Living stromatolite reefs are still found in hot springs and
in warm, shallow pools of fresh and salt water

26. D.1.7 Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere
Fossilized Stromatolites – 3.5 billion years old
Modern day stromatolites

27. Oxygen begins to accumulate 2.7 bya
D.1.7 Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere
Oxygen begins to accumulate 2.7 bya
reducing  oxidizing atmosphere
evidence in banded iron in rocks = rusting
makes aerobic respiration possible
photosynthetic bacteria (cyanobacteria)

28. D.1.7 Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere
first photosynthetic organism were autotrophs which split H2S as a hydrogen donor (purple and green sulfur bacteria)
the first photosynthetic organisms to use H2O as a hydrogen donor were the cyanobacteria (released O2 as by-product)
source of the first free oxygen in aquatic environment and atmosphere – O2 existed in significant quantities by 2 billion years ago

29. The increase in Oxygen led to:
D.1.7 Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere
The increase in Oxygen led to:
The breakdown of the chemicals in the ‘chemical soup’ to carbon dioxide and oxidized sediments
The formation of the ozone layer, which blocked out UV and stopped the production of more of the ‘soupy’ molecules
The oxygen concentration rose to 0.45% of the atmosphere - not much compared to today’s 21%, but it led to the rise of the eukaryotes

30. D.1.8 Discuss the endosymbiotic theory for the origin
of eukaryotes
Endosymbiosis is the theory that chloroplasts and mitochondria were once free-living prokaryotes that were engulfed by larger prokaryotes and survived to evolve into the modern organelles

31. First Eukaryotes Development of internal membranes ~2 bya
D.1.8 Discuss the endosymbiotic theory for the origin
of eukaryotes
First Eukaryotes
~2 bya
Development of internal membranes
create internal micro-environments
advantage: specialization = increase efficiency
nuclear envelope
endoplasmic reticulum (ER)
plasma
membrane
infolding of the plasma membrane
nucleus
DNA
cell wall
plasma
membrane
Prokaryotic
cell
Prokaryotic ancestor of eukaryotic cells
Eukaryotic
cell

32. Endosymbiosis D.1.8 Discuss the endosymbiotic theory for the origin
of eukaryotes
Endosymbiosis
Evolution of eukaryotes
origin of mitochondria
engulfed aerobic bacteria, but did not digest them
mutually beneficial relationship
internal membrane system
aerobic bacterium
mitochondrion
Endosymbiosis
Ancestral
eukaryotic cell
Eukaryotic cell
with mitochondrion

33. Endosymbiosis Evolution of eukaryotes
D.1.8 Discuss the endosymbiotic theory for the origin
of eukaryotes
Eukaryotic
cell with
mitochondrion
Endosymbiosis
Evolution of eukaryotes
origin of chloroplasts
engulfed photosynthetic bacteria, but did not digest them
mutually beneficial relationship
photosynthetic bacterium
chloroplast
mitochondrion
Endosymbiosis
Eukaryotic cell with
chloroplast & mitochondrion

34. Theory of Endosymbiosis
D.1.8 Discuss the endosymbiotic theory for the origin
of eukaryotes
Theory of Endosymbiosis
Evidence
structural
mitochondria & chloroplasts resemble bacterial structure
genetic
mitochondria & chloroplasts have their own circular DNA, like bacteria
functional
mitochondria & chloroplasts move freely within the cell
mitochondria & chloroplasts reproduce independently from the cell