Transcript Chapter 14

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Chapter 14
History of Life
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Biogenesis
Spontaneous
Generation
Radiometric dating
Isotope
Mass number
Radioactive decay
Radioactive isotope
Half-life
Microsphere
Coacervate
Sections 1 & 2
Vocabulary
Pretest
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
The disintegration of an unstable
atomic nucleus
Theory that living things come only
from other living things
Theory that living things can come
from nonliving matter
An isotope with an unstable nucleus
A method of determining the absolute
age of an object
An atom that has the same number of
protons as other atoms of the same
element but different number of
neutrons
Time required for half a sample of
radioactive element to decay
Tiny droplets made of lipids, amino
acids and sugars
Small spheres with a protein
membrane
Number of protons and neutrons in
an atom
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Biogenesis
Spontaneous Generation
Radiometric dating
Isotope
Mass number
Radioactive decay
Radioactive isotope
Half-life
Microsphere
Coacervate
Answer Key
B
C
E
F
J
A
D
G
I
H
Biogenesis vs. Spontaneous Generation
Biogenesis: states that all
living things come from
other living things. It is our
current understanding of
the life process.
 Spontaneous Generation:
states that living things can
arise from nonliving things.
It is a belief held by many
people during the 17th
century

Video Clip
Redi’s Experiment

Francesco Redi (1668): Experimentally
determined that rotting meat does not
spontaneously turn into maggots.
Instead, maggots arise from eggs laid by
other flies.
Spallanzani’s Experiment

Lazzaro Spallanzani (1767): Experimentally
proved that microorganisms do not arise
spontaneously from a “vital force” in air.
Instead the arise from other microorganisms.
Pasteur’s Experiment

Louis Pasteur (1864): Experimentally
proved (without doubt) that broth does
not spontaneously turn into
microorganisms by using an S-shaped
flask.
Earth’s History
So if spontaneous generation
does not happen on Earth
today, then how did cellbased life arise in the first
place?
 Scientists believe the answer to
this question lies in the
scientific belief that Earth was
a very different place billions
of years ago.
 We need to briefly trace
Earth’s History to understand.

The Formation of Earth
5 billion years ago:
universe was a swirling
mass of gas and dust
which, overtime, was
pulled together by gravity
to form the sun.
 Planets formed from the
remaining dust and debris
as it circled the sun and
collided repeatedly
 Earth is estimated to be
more than 4 billion years
old

Radiometric Dating

Radiometric Dating: a technique used to establish the
absolute age of an object by comparing the relative
percentages of a radioactive isotope and a stable isotope.
 Atomic Number = number of protons in the nucleus of
an element. Atoms of the same element always have
the same number of protons…but the number of
neutrons can vary, creating isotopes.
 Radioactive isotopes are unstable: their nuclei will
release particles or radiant energy in order to become
more stable. This is called radioactive decay.

Rates of decay have been determined for
many radioactive isotopes and half-lives
have been established.
 Half-life = length of time it takes for
one-half of any size sample of an
isotope to decay to a stable form.
 Carbon is a common element used in
radiometric dating.
Carbon-14 Dating

Organic material can be dating by comparing the amount of carbon14 (unstable) with the amount of carbon-12 (stable)
 Living things constantly take in carbon (mostly C-12 and a
small amount of C-14)
 The ratio of C-12: C-14 in living things is known and fixed.
 When a living thing dies, it stops taking in carbon. The decay of
C-14, however, continues.
 Thus the ratio will change: the amount of C-14 will decline with
respect to the amount of C-12.
 The half-life of C-14 is 5,730 years. We can use C-14 dating for
objects less than 60,000 yrs old.
 Isotopes with longer half-lives are used to date older rocks.
First Organic Compounds
Alexander Oparin: proposed the
first idea on the origin of organic
compounds. He hypothesized
that the many gases present in
Earth’s early atmosphere, under
very high temperatures, might
have formed simple organic
compounds such as amino acids.
 These would have collected in
lakes and seas as Earth cooled,
and over time, fueled by energy
from lightening and UV
radiation, could have formed
larger molecules such as
proteins.

Miller and Urey’s Test
Stanley Miller and Harold
Urey (1953): Tested Oparin’s
hypothesis with the “electric
spark experiment”. They
succeeded in producing
amino acids from the gases
believed to have been
present in Earth’s early
atmosphere.
 Similar and more recent tests
have produced amino acids,
ATP and nucleotides from
these same gases.

Organic Compounds from Space

In 1970, organic
compounds were
discovered in a recently
fallen meteorite,
suggesting that organic
compounds exist in space
and could have
accumulated on early
Earth with fallen
meteorites.
From Molecules to Cell-like Structures

How did the organic molecules of
early Earth give rise to cells?
 Sydney Fox: discovered the
spontaneous formation of cell-like
structures known as microspheres
and coacervates from solutions of
organic molecules.
 These structures are surrounded
by membranes made of lipids and
can take up certain substances
from their environment. They can
grow in size and form buds that
break off.
 This shows that some of the
important properties of life could
have arose without the direction of
genes.
microspheres
coacervates
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2.
3.
4.
5.
6.
Ribozyme
Archaea
Chemosynthesis
Cyanobacteria
Ozone
Endosymbiosis
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B.
C.
D.
E.
Section 3
Vocabulary
Pretest
F.
Photosynthetic, unicellular
prokaryotes
RNA molecule that can act as a
catalyst for a chemical reaction
A gas molecule made up of three
oxygen atoms
Ancient prokaryotes that live in
extreme environments
Theory to explain how eukaryotic
cells originated
Production of carbohydrates
through the uses of energy from
inorganic molecules instead of light
1.
2.
3.
4.
5.
6.
Ribozyme
Archaea
Chemosynthesis
Cyanobacteria
Ozone
Endosymbiosis
Answer Key
B
D
F
A
C
E
The First Life-Forms
The final transition from organic
molecules to living cells is the
origin of heredity.
 A closer look at RNA has led
scientists to discover that some
types of RNA, called ribozymes,
act as catalysts (similar to
enzymes)
 Some can catalyze their own
replication and thus life could
have begun with some form of
self-replicating RNA

The First Cells

It is believed that the first
true cells were probably
anaerobic, heterotrophic
prokaryotes
 They fed on
spontaneously formed
organic molecules…and
probably used them up
quickly.
 This would quickly favor
autotrophs similar to
today’s archaea
Archaea and Chemosynthesis
Archaea are unicellular
prokaryotes that thrive
under extremely harsh
environmental
conditions.
 They get energy by
chemosynthesis, using
CO2 as a carbon source
and oxidizing inorganic
chemicals like sulfur.
 The oldest fossils are
those of archaea

Photosynthesis
3 billion years ago, living cells began to
photosynthesize
 The first photosynthetic organisms were similar
to today’s cyanobacteria.
 Cyanobacteria live in large colonies and form
structures called stromatolites.
 Fossil stromatolites are 3.5 billion years old
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
As the oxygen produced by photosynthesis
reached the upper atmosphere, it formed
ozone, which was essential for life to continue
to evolve on Earth.
The First Eukaryotes

Endosymbiosis: Theory proposed by Lynn
Margulis which states that eukaryotic cells
developed from a mutually beneficial
relationship between small, aerobic prokaryotes
living inside larger, anaerobic prokaryotes
Endosymbiotic Theory
Mitochondria and Chloroplasts may have developed from this relationship.