2. Biogenesis vs. Spontaneous
Generation
Definition: All living Definition: Living things
(biotic) things come can arise (come
from other living things. from)nonliving (abiotic)
Common sense today, things.
not believed in the 17th Observations that
century. supported the belief:
Experiments conducted Maggots appeared on
to prove biogenesis. rotting meat, fish
appeared in seasonal
ponds.
3. Francesco Redi - 1668
Addressed maggots appearing on meat.
Initial observation: Maggots appear on meat after flies
have landed.
Hypothesis: Maggots come from flies NOT meat.
Experiment: Placed meat in an open jar and in a jar that
was covered with cheese cloth.
Control Group
Experimental Group
4. More Proof Needed…
Microscope was invented around same time as Redi’s
experiment.
Scientists began observing ‘tiny creatures’.
Accepted Redi’s conclusion but not for microscopic
organisms.
Believed microorganisms arise spontaneously from a
“vital force” in the air.
5. Lazzaro Spallanzani(1729 -1799)
Initial observation: Microorganisms grow easily in
food.
Hypothesis: Microorganisms formed not from air but
from other microorganisms.
Experiment: Placed broth in two flasks, boiled broth,
one flask left open, the other sealed closed.
Control Group:
Experimental Group:
6. Still not convinced…..
Spallanzani concluded that the boiled broth became
contaminated only when microorganisms from the air
entered the flask.
Opponents objected to his method and disregarded
his conclusion.
Opponents claimed that Spallanzani had heated the
flasks too long and destroyed the “vital force” in the air
inside the flasks.
Belief in spontaneous generation continued for
another 100 years. Until………
7. Controversy grows Fierce!
By mid-1800’s the arguments over S.G. were fierce.
Paris Academy of Science offered a prize (equivalent to
$1 million today) to anyone who could clear up the
issue once and for all.
The winner: Louis Pasteur.
Why is that name familiar to you?
8.
9. Pasteur’s Experiment
Observations and hypothesis were the same as
Spallanzani’s.
To answer the objections to Spallanzani’s experiment,
Pasteur made a curve-necked flask.
Air from outside can mix with inside.
Curve in the neck prevented solid particles, such as
microorganisms, from entering the body of the flask
with the broth.
Finally, BIOGENESIS became a cornerstone of biology.
11. Formation of Earth
Earth is believed to be 4.56 billion years old.
Earth took 400 million years to form from gas, dust
and debris circling the sun.
Earth grew as it was bombarded with debris.
Each collision released enough energy to melt the
surface of the forming planet.
Estimates of Earth’s age made from studying layers of
sediment in the crust.
Accurate estimate through radioactive dating.
12. Radioactive (Radiometric) Dating
Isotopes: atoms of the same element (same atomic
number or number of protons) but differ in number of
neutrons.
Mass number = protons + neutrons
Is0topes are designated by chemical name followed by
their mass number.
Example: carbon -12 and carbon- 14.
Radioactive Decay: isotopes with unstable nuclei
(protons and neutrons in center) tend to release
particles or radiate energy (decay)
13. Radioactive Dating cont.
Rates of decay of many radioactive isotopes have been
determined.
Half-life: the length of time it takes for ½ of any size
sample of an isotope to decay.
Can range from fraction of a second to billions of years
but is specific to each isotope.
Age of material is determined by measuring amount of
a particular radioactive isotope it contains and
comparing it to the amount of some other substance in
the sample that remains constant.
14. Radioactive Dating cont.
http://science.discovery.com/videos/100-greatest-
discoveries-shorts-radiometric-dating.html
If the history of the earth were condensed to a 24 hour
clock, how long have humans been on the planet?
15. First Organic Compounds
All elements found in organic compounds are thought
to have existed on Earth and in the rest of the Solar
System when Earth formed.
How and where did these elements assemble into
organic compounds found in life?
Oparin hypothesized in 1923, Urey and Miller
experimented in 1953 to test Oparin’s hypothesis.
http://science.discovery.com/videos/100-greatest-
discoveries-shorts-origin-of-life.html
16. The first cells.
Little to no oxygen gas when they first arose so…….
The first cells were anaerobic.
Small size of the oldest microfossils indicate the first
cells were prokaryotes (no nucleus).
First cells were heterotrophs, consuming organic
molecules from their environment.
Autotrophs evolved due to strong pressure in the
environment (competition for food).
First autotrophs performed chemosynthesis.
17. Photosynthesis and Aerobic
Respiration
Photosynthesizing autotrophs evolved and put oxygen
into the atmosphere (around 3.5 billion years ago).
Took billions of years for oxygen gas to reach today’s
levels.
Oxygen was dangerous to many early organisms
because it could destroy coenzymes essential to cell
function.
Oxygen bonded to other compounds in some
organisms, preventing damage, this was the first step
to aerobic respiration.
18. The first eukaryotes.
2 to 1.5 billion years ago.
Small aerobic prokaryote entered and began to live and
reproduce inside larger, anaerobic prokaryotes.
Mutually beneficial relationship – endosymbiosis
Small aerobic prokaryote = today’s mitochondria
(remember they have their own DNA)
Similar situation for chloroplast in photosynthetic cells.
http://videos.howstuffworks.com/discovery/29535-
assignment-discovery-prokaryotes-the-first-cells-
video.htm
