Download Capturing Solar Energy: Photosynthesis

Capturing Solar
Energy:
Photosynthesis
(a)
Photosynthesis
(b) internal leaf structure
mesophyll
cells
(c) chloroplast in
mesophyll cell
outer membrane
inner membrane
thylakoid
stroma
vein
stoma
chloroplasts
•
•
channel
interconnecting
thylakoids
Life depends on
photosynthesis
Photosynthesis
•
Light energy captured and stored as
chemical potential energy in the
covalent bonds of carbohydrate
molecules
6 CO2 + 6 H2O + light → C6H12O6 + 6 O2
Complex series of chemical reactions
involving a transition in forms of
energy
Uses light energy to make food and is a
process by which some organisms can
make organic compounds from simple
inorganic compounds using energy
from the sun
•
A. Foundation of energy for most
ecosystems
•
B. Source of oxygen
•
C. Key component of the carbon cycle
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The mechanism of
photosynthesis
•
•
Solar energy and light
The electromagnetic spectrum
–
Pigment molecules absorb some
wavelengths of light and reflect others
•
Chlorophyll—a green photosynthetic pigment
associated with the thylakoid membranes of
chloroplasts
(b)
chlorophyll
carotenoids
phycocyanin
(a)
(c)
The mechanism of
photosynthesis
• Chloroplasts are the sites of photosynthesis
– Have a membrane system within internal space (stroma)
– Arranged in disk-shaped sacks (thylakoids)
• The thylakoids contain light-harvesting photosynthetic
pigments & enzymes
• Internal membranes define space (lumen) that is
separate from the rest of the stroma
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chloroplast
The mechanism of
photosynthesis
thylakoids
Photosynthesis occurs in two steps
1. Light-dependent reactions
reaction
center
electron transport system
light- harvesting
complex
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electron transport
system
3
reaction
center
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energy to drive
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synthesis
reaction
center
a. Provides the energy necessary to fix carbon
•
b. Occurs in the thylakoid membranes
•
c. Generates ATP
•
d. Photolysis—light, electrons and water
The mechanism of
photosynthesis
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2
•
photosystem I
Energy carriers ATP and NADPH
transport energy from the lightdependent reactions to the lightindependent reactions
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photosystem II
energy from
sunlight
The mechanism of
photosynthesis
2. Light-independent reactions
Light-dependent
reactions occur
in thylakoids.
Light-independent
reactions (C3cycle)
occur in stroma.
a. Uses energy of the light-dependent
reaction to make sugar from CO2
b. Occurs in the stroma
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1
3
Carbon fixation
combines CO2
with RuBP.
RuBP
regeneration
uses energy
and 10 G3P.
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C4 plants utilize an alternate
pathway to make sugars in dry
environments
• Closing stomata to conserve water
results in photorespiration in C3
plants
G3P synthesis
uses energy.
2 G3P available
for synthesis of
organic molecules.
(a) C plants use the C pathway
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mesophyll cell in C3 plant
The History of Life on Earth
Much
photorespiration
occurs under hot,
dry conditions.
In a C3 plant, most chloroplasts are in
mesophyll cells.
mesophyll cell in C4 plant
(b) C plants use the C pathway
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CO2 is captured
with a highly
specific enzyme.
bundlesheath
cells
In a C4 plant, both mesophyll
and bundle-sheath cells
contain chloroplasts.
Much glucose
synthesis occurs.
Almost no
photorespiration
occurs in hot,
dry conditions.
When did life arise on
Earth?
• The Earth is thought to
be approximately 4.6
billion years old, but life
is believed to have
occurred approximately 4
billion years ago (bya)
•How did life begin???
bundle-sheath cell in C4 plant
The Origin of Life: Early Ideas
• Spontaneous Generation
Francesco Redi experiment with
flies and wide-mouth jars
– idea popular in the 1600-1700’s
– living things come from the nonliving
– evidence: beetles and other insect larvae arise from
cow dung; frogs emerge from mud
• In 1688, the Italian Francisco Redi In 1668,
Francesco Redi, an Italian physician, did an
experiment with flies and wide-mouth jars. He
demonstrated that meat that was covered did
not produce maggots
• This may have been the first true scientific
experiment…
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The Origin of Life
Spontaneous generation
• Mid-1800s—disproved by Louis Pasteur and
John Tyndall
no growth
Broth in flask is boiled
to kill preexisting
microorganisms.
growth
Condensing water collects
as the broth cools, sealing
the mouth of the flask.
If neck is later broken off,
outside air can carry
microorganisms into broth.
Origin of Life:
Another idea
Other Ideas: Life from a
Biblical Creation?
Christian Creationism states
that the world, including all
life, was created about 6,000
years ago in six literal days
by a God.
…But how does one accurately
and fairly test for this?...
What’s the observation,
hypothesis, test…?
This idea does not really fit into
the confines of a Science
course.
Like the study of French Impressionist
painters, Religion is not part of, nor
adequately covered in, a Science course.
Biogenic-looking features in
ALH84001 Martian meteorite
http://ares.jsc.nasa.gov/astrobiology/biomarkers/images.html
Extra-terrestrial Origins
In 1969, a meteorite (left-over bits from the origin of the
solar system) landed near Allende, Mexico. The Allende
Meteorite (and others of its sort) have been analyzed
and found to contain amino acids, the building blocks
of proteins.
This idea of panspermia hypothesized that life originated
out in space and came to earth inside a meteorite. The
amino acids recovered from meteorites are in a group
known as exotics: they do not occur in the chemical
systems of living things. The ET theory is now
discounted by most scientists, although the August
1996 discovery of the Martian meteorite and its
possible fossils have revived thought of life elsewhere
in the Solar System.
Anyway….This only moves the problem to elsewhere!
The Latest on Extra-terrestrial
Origins…
The Raelians
• Raelians believe that humanity
was created from the DNA of
superior alien scientists
• Follow the teachings of a
former French magazine
sportswriter and wannabe
race-car driver Claude
Vorilhon, 56. He took the
name "Rael" after he claimed
a close encounter of the third
kind….
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Origin of Life: Current Theory
• Chemical Evolution
• .....The idea that long ago complex
collections of chemicals formed the first
cells.
• Life began in the oceans 4 bya from
simple chemicals joining together in a
“primordial soup”
• Complex chemicals evolved into living
cells
What were the conditions like on Earth when life arose?
• Up to about 4 bya, asteroid impacts and volcanic eruptions resulted
in the release of various gases that began to form an atmosphere
• It consisted mainly of CO2, with some nitrogen, water vapor and
sulfur gases; hydrogen quickly escaped into space
• CO2 in the atmosphere trapped solar radiation, making the Earth’s
surface rather warm
• Earth was cool enough to form a crust, and water vapor condensed
to form oceans
• Oceans in turn helped to dissolve CO2 from the atmosphere and
deposit it into carbonate rocks on the seafloor
The Origin of Life
What were the conditions like on Earth when life
arose?
• Organic molecules were undoubtedly being
formed on the Earth’s surface
• Lightening and ultraviolet radiation from the Sun
acted on the atmosphere to forms small traces of
many different gases, including ammonia (NH3),
methane (CH4), carbon monoxide (CO) and ethane
The possible origin of
organic molecules
•
a. 1953—the
Stanley Miller
experiment
• Also, cyanide (HCN) probably formed easily in the
upper atmosphere, from solar radiation and then
dissolved in raindrops
What is the simplest living cell that one can imagine?
The Origin of Life
Early Speculations
A universal minimal cell
must contain the following::
• Cell membrane
• Cytoplasm
• DNA and RNA
• Proteins
• Enzymes
• Ribozymes
• More circumstantial evidence
accumulated
– Astronomers found simple organic
compounds in meteorites
– They were convinced that Earth’s initial
atmosphere could not have matched
Oparin-Haldane’s model
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The Origin of Life
The Origin of Life
Early Speculations
Early Speculations
• More circumstantial evidence
– Fossils of ancient bacteria (3.5 billion years old)
were found in Australia
– Suggested life may have evolved rapidly in less
than a billion years
• What are the possible scenarios?
– When ocean tidal pool evaporates
• Salts get highly concentrated
– Could have happened in ancient
oceans
• Concentrating aminos, may allow
protein to form
The Origin of Life
Early Speculations
• Phospholipids arrange themselves into bubbles
– Chemicals could be concentrated in bubbles (might
contain protein, etc.)
– These bubbles would persist aided by natural selection
– If they burst, spew contents into air where other
reactions occur
– Over hundreds of millions of years, similar processes
could have filled oceans with proteins, carbohydrates,
phospholipids, nucleotides
The Origin of Life
Early Speculations
• Is DNA essential?
– Scripps Institute, 1993 found small
molecules of synthetic RNA that within an
hour began making copies of itself & the
copies made more copies
– Then copies began to change - evolveacquiring new chemical characteristics,
but not alive
The Origin of Life
Early Speculations
• Phospholipids arrange themselves into
bubbles
– Eventually they reach a level of
complexity
• Called protocells (not living)
• Still can’t reproduce, no DNA
The Origin of Life
Early Speculations
• Is DNA essential?
– Protocells might qualify as the first cells if they have
RNA that:
• Can make copies of itself & evolve
• Could synthesize enzymes capable of breaking down
other organic compounds
• Could synthesize enzymes capable of building and
maintaining cell membranes
– Later DNA could have evolved as method of
conveniently & safely
• Storing vital chemical info contained in cell RNA
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The Origin of Life
The First Cells
Early Speculations
•
Age of microbes—3.5 billion years ago
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1. The earliest living cells—anaerobic
prokaryotes
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2. Photosynthetic bacteria and the
evolution of an oxygen-rich environment
•
3. Development of aerobic metabolism
1. Anaerobic, predatory
prokaryotic cell engulfs
an aerobic bacterium.
II. The first cells
aerobic
bacterium
• The rise of eukaryotes—about
1.4 billion years ago
2. Descendants of engulfed
bacterium evolve into
mitochondria.
• 1. Endosymbiotic hypothesis
3. Mitochondria-containing
cell engulfs a photosynthetic
bacterium.
• 2. The origin of the nucleus
4. Descendants of photosynthetic
bacterium evolve into chloroplasts.
First Cell Types
• Heterotrophic cells
– Incapable of producing their own food
• Autotrophs
– Can produce chemicals to store energy
• Chemoautotrophs
– Store energy found in certain inorganic chemicals
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First Cell Types
• Most organisms found free oxygen intolerable
– In oceans
• Organisms that built simple and complex organic
compounds
Further Evolution of First Cells
• First cells, prokaryotes, were always simple
in structure
• 2 - 1.5 billion years ago
– A new cell appeared – eukaryotes
– Had membranes to isolate certain chemical
reactions
• Removed CO2 from the atmosphere
• More advanced autotrophs removed most of the rest
& replaced it with oxygen
• The excess oxygen changed forever chemical nature
of atmosphere to today’s
• Cellular life then evolved into what we know
today
Multicellular organisms
Archaea & Bacteria Domains
• Directly related to oldest organisms on
earth
– Have had lots of time to evolve & differentiate
•
A. Advantages of multicellularity
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B. Challenges of multicellularity
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C. The first multicellular organisms
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•
• Thrive nearly everywhere
– Depths of oceans & Earth, all surfaces
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III. Multicellular organisms
1. Plants—primitive marine algae
2. Animals—marine invertebrates
D. The transition to land
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1. Advantages of terrestrial living
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2. Challenges of terrestrial living
III. Multicellular organisms
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The transition to land
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D. The transition to land
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The evolution of land plants
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The evolution of terrestrial animals
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a. The first land plants
• 1) Mosses and ferns
• 2) Continued water dependency
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b. Conifers—the invasion of dry habitats
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c. Flowering plants
• 1) The dominant plant form today
• 2) Pollination by insects
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a. Arthropods
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b. Lobefin fish to amphibians
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c. Amphibians to reptiles
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1) The age of the dinosaurs
2) Reptiles and maintenance of body temperature
d. Birds
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•
1) Insulating feathers retain body heat
2) Evolution of feathers for flight
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Era
Period
Millions of
years ago
Cenozoic
Quaternary
Today
III. Multicellular organisms
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e. Mammals
Current extinction crisis caused
by human activities. Many species
are expected to become extinct
within the next 50–100 years.
Extinction
Tertiary
Extinction
65
Jurassic
Cretaceous: up to 80% of ruling
reptiles (dinosaurs); many marine
species including many
foraminiferans and mollusks.
Extinction
180
Triassic: 35% of animal families, including
many reptiles and marine mollusks.
Triassic
Extinction
250
• 1) Insulating hair retains body heat
Permian: 90% of animal families, including
over 95% of marine species; many trees,
amphibians, most bryozoans and
brachiopods, all trilobites.
Permian
Carboniferous
Paleozoic
• 2) Live births and mammary glands
Species and families experiencing
mass extinction
Cretaceous
Mesozoic
The evolution of terrestrial animals
Bar width represents relative
number of living species
Extinction
345
Devonian: 30% of animal families,
including agnathan and placoderm
fishes and many trilobites.
Devonian
Silurian
Ordovician
Extinction
500
Cambrian
Ordovician: 50% of
animal families,
including many
trilobites
H.habilis
IV. Human evolution
H.sapiens
Homo ergaster
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•
A. Primate evolution
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H. heidelbergensis
Australopithecus
afarensis
1. Grasping hands—precision grip and
power grip
H. neanderthalensis
H. erectus
A. robustus
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2. Binocular and color vision with
overlapping fields of view
Ardipithecus
ramidus
A. africanus
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3. Large brain—allows fairly complex social
systems
A. boisei
IV. Human evolution
IV. Human evolution
• Hominid evolution
• 1. The evolution of dryopithecines—between
20 and 30 million years ago
• 3. Homo habilis—2 million years ago
• 2. Australopithecines—the first true hominids
• 4. Homo erectus—1.8 million years ago
• a. Appeared 4 million years ago as evidenced by
fossils
• b. Walked upright
• c. Large brains
• a. Larger body and brain
• b. Ability to make crude stone and bone tools
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•
•
•
a.
b.
c.
d.
Face of modern human
More socially advanced
Sophisticated stone tools aided in hunting
Used fire
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IV. Human evolution
5. Homo sapiens—200,000 years ago
• a. Neanderthals evolved 100,000 years ago
•
• 1) Similar to humans–muscular, fully erect,
dexterous, large brains
• 2) Developed ritualistic burial ceremonies
• b. Cro-Magnons evolved 90,000 years ago
• 1) Direct descendants of modern humans
• 2) Were artistic and made precision tools
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