1. 1.5 The origin of life
Essential Idea: There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today.

2. Cells can only be formed by the division of pre-existing cells.
Cellular origins
?????
The cell theory dictates three things:
The cell is the most basic unit of life.
All organisms are made of one or more cells.
All cells come from pre-existing, living cells.
Wait….if all cells came from pre-existing cells, then where did the first cell come from?
If we can trace that zygote back to the sex cells that our parents produced, and we can trace the origin of all the cells in their bodies back to the cells in their parents bodies……etc. etc. and so forth, why can’t we just go back to the first life form?

3. Experimental setup: The theory of Spontaneous Generation of Life
Design an experiment to test the following hypothesis:
Life can exist anywhere there is food and water. Life will spontaneously generate anywhere these conditions are met.
What would you control?
How would you set up your experiment?
What result would support your hypothesis? What result would refute your hypothesis?

4. Louis Pasteur – scientist in the 1800s hypothesized about the origin of life and set out to test that very same hypothesis
Humans thought for many years that life had spontaneously come about, out of nothing.
This guy performed a series of experiments to prove that spontaneous generation of organisms does not still occur on Earth. Using these swan-necked flasks

5. Experimental setup
Pasteur found that nutrient broth in a sealed flask would remain unchanged, whereas nutrient broth when exposed to air, would show bacterial growth
This proved that cells only come from pre-existing cells

6. The first cells must have arisen from non-living material.
A logical conclusion
Assuming aliens are not the source of life on the planet, life must have arose from non-living material
4 Stages:
Production of carbon compounds, such as sugars and amino acids
Assembly of carbon compound polymers
Formation of membranes
Development of a mechanism for inheritance
However – This methodology requires us to make the jump from chemical evolution to biological evolution.
Science still has not experimentally proven this jump.
1st Stage
2nd Stage
3rd Stage
4th Stage

7. Step 1 - Production of simple carbon compounds occurred naturally in the early atmosphere and water.
The early atmosphere was very different from the modern one.
It was mostly composed of Methane, Sulfurous compounds and Ammonia
The early earth also had tons of energy flowing into it in three major forms:
Lightning
Geothermal Heat
Light Energy
If you combine these simple compounds with enough energy, they will collide, creating simple compounds. Over enough repetitions, you have a phenomenon known as Chemical Evolution, where certain chemicals are made and stay around.

8. Step 1 - Production of simple carbon compounds occurred naturally in the early atmosphere and water.
Scientists sought to experimentally support this first step, and the first to do so were the pair, Miller and Urey.
3. Electricity run through
organic compounds as a
vapor
2. Organic Compounds
heated
4. Water condensed
and sampled
1. Organic compounds
introduced

9. Check out this video in order to be able to answer the following questions:
What was the goal of the Miller-Urey Experiment?
What evidence did the Miller-Urey Experiment provide against the theory of Spontaneous Generation?
What were the discoveries of this experiment?

10. Step 2 - Assembly of carbon compounds into more complex polymers.
Polymer – multi-unit molecule, consisting of two or more repeating parts
Hydrothermal vents – provide surplus of energy in form of heat, and reagents in the form of chemicals
In what way are the modern hydrothermal vents analogous to the ancient atmosphere?
How do the organisms get their energy?
Yay – Attenborough!

11. Step 3 – Membranes formed, causing for a separation of the inside and the outside of the cavity.
If phospholipids were among some of the carbon compounds created, then they would naturally form into a bilayer membrane due to it being the most energy-favorable position for them
These membranes would allow for a different chemistry to be created internally as compared to the surroundings
Liposome formation video
Liposomes in 3D configuration

12. Step 4 – These “bodies” must have developed a mechanism for inheritance.
Cells originally only possessed RNA, which can replicate itself and act as its own catalyst for the process of replication.
It would not be until much later that DNA was in use in cells, due to the fact that it needs much more complex mechanisms for its replication and operation

13. Endosymbiosis = “within” + “mutually beneficial relationship”
The origin of eukaryotic cells can be explained by the endosymbiotic theory.
Endosymbiosis = “within” + “mutually beneficial relationship”
The origin of eukaryotic cells can be explained by the endosymbiotic theory.
This states that mitochondria and chloroplast were once separate individual organisms, which were engulfed by larger prokaryotic organisms
Which type of cells did human cells come from?

14. Why is it mutually beneficial?
Inquiry Activity – Endosymbiotic Theory
Your Task – To prove whether the endosymbiosis of mitochondria and chloroplast is worth or not.
Determine the following:
Benefit to eukaryotic cells
Benefit to mitochondria
Benefit to chloroplast
Detriments to any of the above elements
Compose your argument in a brief argumentative statement to the following, based on your research:
Was the endosymbiosis of chloroplast and mitochondria worth for eukaryotic cells? Was it more beneficial to larger organisms or smaller organisms?
Finally, respond to the following statement:
Animal cells are more evolved than plant cells.
Use your research to either agree or disagree with the above statement. ? ? ? ? ? ?