How Life began
Spontaneous Generation

Definition: non-living material
can produce life.

AKA – abiogenesis

This was the accepted theory
for a very long time!
 Not
much was known
about reproduction

There are 2 experiments that
helped disprove this (or prove
biogenesis)
Frencesco Redi (1668)
Early
scientists thought maggots
came from rotting meat.
Redi proved that maggots came
from fly eggs not rotting meat
His experiment
 Place
rotting meat in 2
 Cover
1 and leave 1
jars.
open
 Flies
appeared on the
mesh on the covered
jar and they appeared
on the meat in the
uncovered jar, but NOT
on the sealed jar.
Redi’s conclusion
Rotting Meat could not produce
flies.
Flies came to the meat and laid
eggs.
Disproved spontaneous
generation

Louis Pasteur
 After
Redi, scientists accepted large
organisms didn’t come from nonliving
material, but they still questioned
microorganisms.
 So he wanted to prove that
microorganisms were living and also
needed to come from other living
things.
His experiment

Fill a S-shaped flask with meat
broth

Boil it (why?)

The flask allowed air to come
into contact with broth but it did
not allow microorganisms to
enter because they were
trapped in the curve.

Tilt the flask or break the top of
the flask

Notice air and broth becoming
cloudy with the micoorgansims.
Conclusion:
 Living
microorganisms do not come
from non-living material
 Supports biogenesis
 Interesting fact: he came up with
pasteurization!
Pasteurization:
using heat to kill microbes
in food and drink
So then, where did the first life
come from?

Miller and Urey’s
theory (1953)

They experimented
their theory that the
first life arose from
small pools of water
on early earth.
Their experiment:

They created an atmosphere like early earth.

It contained: water vapor, ammonia, methane and
Hydrogen.

They exposed this gas mixture to electricity that simulated
lightning.

Then, heated and cooled that mixture just like the daily
water cycle.

There was no oxygen present during any part.

This created organic compounds that were called amino
acids.

https://www.youtube.com/watch?v=xyhZcEY5PCQ
So from here...
 Endosymbiotic
theory: that certain
organelles that are found in today’s cells
originated from free-living bacteria.
 Ex:
Aerobic bacteria emerged into the
mitochondria in ancient eukaryotes.
 EX:
photosynthetic bacteria emerged into
chloroplast found in primitive eukaryotes
Overall idea of Endosymbiotic
theory:
 First
there was anaerobic organisms (didn’t
need oxygen) and prokaryotes (Bacteria)
 Then photosynthetic bacteria
 Next eukaryotic single cells
 Then eukaryotes with endosymbiotic
organelles
 Mitochondria
 Chloroplasts
 Last
(protists and plants)
multicellular organism
Tree of Life video