Photosynthesis
Sci 190 E
Lecture 13
photo-synthesis – building by light
Plants
Algae
Bacteria
CO2 + H2O
light
(CH2O) + O2
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Photosynthesis: main source of energy
Photosynthesis:
• Annually fixes 1011 tons of carbon
•
stores 1018 kJ of energy
• Equivalent to 30,000 GW power plant
• Fossil fuel: coal, oil, gas
Annual energy consumption in 2002
Year 2002
US (kJ)
World (kJ)
Petroleum
0.45 × 1017 1.62 × 1017
Gas
0.24 × 1017 1.00 × 1017
Coal
0.25 × 1017 1.03 × 1017
Hydroelectric
0.01 × 1017 0.28 × 1017
Nuclear electric
0.03 × 1017 0.28 × 1017
~1/3 of total
photosynthesis
(1018 kJ)
Geo, solar, wind… 0.003×1017 0.03 × 1017
Total
1.08 × 1017 4.27 × 1017
Sunlight falling on Earth surface is ~4 ×1021 kJ/year
(~1 kW/m2)
http://www.eia.doe.gov/iea/overview.html
http://www.cslforum.org/usa.htm
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Carbon dioxide emission
All of oxygen in the atmosphere was produced by photosynthesis!
Photosynthesis annually fixes ~ 1011 tons of carbon
Using gas, coal, oil as energy source reverses natural process, burns
oxygen and emits CO2 (‘green house effect’)
Year 2002
Carbon emission:
USA 1.6 × 109 ton
World 7 × 109 ton
Why study photosynthesis?
Learn from nature:
how to build truly environmentally safe sources of energy
(biomimetic devices - devices that mimic biological systems)
Curiosity
3
History of photosynthesis
research
Major advances in understanding photosynthesis (and
biological systems in general) occur when new knowledge and
techniques from other sciences (physics, chemistry…) are
applied to biological systems
Discovery of photosynthesis: van Helmont
Joean Baptista
van Helmont
169 lb
Belgian physician
Pioneer chemist
“Willow” experiment:
5 lb
5 years
rainwater only
1579-1644
200 lb
of dry soil
200 lb - 2 ounces
of dry soil
Conclusion: 164 pounds of wood, bark, and roots, arose out of water
only.
http://mattson.creighton.edu/History_Gas_Chemistry/vanHelmont.html
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Discovery of photosynthesis: van Helmont
Joean Baptista
van Helmont
1579-1644
Hypothesis:
Water is the only nutrient for plant growth
http://www.howe.k12.ok.us/~jimaskew/botzo/botphoto.htm
Discovery of photosynthesis: John Woodward
Physician and geologist, Cambridge University
1665 - 1728
One plant showed a mass gain of about 1 gram,
while Woodward had added a total of almost
76,000 grams of water during the 77 days of
plant growth.
Conclusion:
• water was “drawn off and conveyed through the pores of the
leaves and exhaled into the atmosphere.”
• “We may very reasonably infer, that Earth, and not Water is the
matter that constitutes Vegetables. … Water serves only for a
Vehicle to the terrestrial Matter which forms Vegetables; and
does not itself make any addition unto them.”
Need better experiment to control water consumption!
http://www2.nsta.org/Energy/find/primer/primer2_5.html
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Discovery of photosynthesis: Microscope
Progress relies on experimental methods
End of the 17th century: invention of microscope
Robert Hooke
1665: Published “Micrographia”
Hooke’s microscope
1635-1703
drawing of cells in cork
Hooke was the first to observe cells
Discovery of photosynthesis: Marcello Malphigi
Italian anatomist and biologist
Observation (~1670): When the first green
leaves of a squash seedling were cut off, the
seedling did not grow, even though its roots
still had free access to water and soil
Hypothesis: leaves of a plant are its nutritive
organs
Microscopic observations:
Hypothesis: plant tissue may be cellular
1628-1694
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Discovery of photosynthesis: Microscope
Improvement of a microscope
Anton Van Leeuwenhoek
Focus knob
Lens
Sample holder
270x magnification!
Sample translator
1632-1723
Discovery of photosynthesis: Nehemiah Grew
English botanist
microscopic studies of the internal structure
of plants in the 1670'
s:
Leaves have many openings
1641 - 1712
“[T]he skins of at least many plants are formed with several
orifices or passports, eithre for the better alveolation [evaporation]
of superfluous sap, or the admission of air.”
http://www2.nsta.org/Energy/find/primer/primer2_6.html
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Discovery of photosynthesis: Stephen Hales
English physiologist, chemist
“Father” of plant physiology
1727: published “Vegetable Staticks”
1677–1761
“the leaves and stems of plants
do imbibe elastic air”
water
mercury
Was able to measure the
‘sucking’ power of plants
http://www.hcs.ohio-state.edu/hort/history/108.html
Discovery of photosynthesis: J. Priestley
Joseph Priestley
• Never took any science course
• Minister in a small church in Leeds
• 1766: met Benjamin Franklin in London
became interested in science
• 1767: graphite conducts electricity
published “The history of electricity”
• 1770: “rubber” (eraser)
1733 – 1804
• Carbon dioxide, soda
• 1772: elected to French Academy of Sciences
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Discovery of photosynthesis:
Priestley’s 1771-1772 experiments
1. Candle in an enclosed space burns out
2. Mouse in an enclosed space suffocates
http://www2.nsta.org/Energy/find/primer/primer2_7.html
Discovery of photosynthesis:
Priestley’s 1771-1772 experiments
Conclusions:
• Air is consumed and somehow “injured”
• “[A]n ordinary candle consumes … about a gallon [of air] in a
minute. Considering this amazing consumption of air, by fires of
all kinds, volcanoes, etc. it becomes a great object of … inquiry
to ascertain what change is made in … the air by flame, and to
discover what provision there is in nature for remedying the
injury which the atmosphere receives …”
• Hypothesis: plants restore air
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Discovery of photosynthesis:
Priestley’s 1771-1772 experiments
3. Candle and mint plant
27 days
4. Mouse and mint plant
5. Mouse needs plant
Plant needs mouse
Priestley’s conclusions
Plants ‘repair’ air (produce oxygen)
Burning ‘injures’ air (burns oxygen and produces carbon dioxide)
Drawback: he believed in ‘phlogiston theory’:
every flammable substance contains phlogiston
that is released into air by burning
phlogiston
1782: publishes “History of Corruptions of Christianity”
book was officially burned in 1785
1791 - his home and church were burned (support of American and French revolutions)
1794 - moved to US
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Discovery of photosynthesis: Antoine Lavoisier
Wealthy family
1773: Repeated Priestley’s experiments
Burning = combining with oxygen!
named in 1779
‘acid-former’
1783: Proved phlogiston theory to be wrong
1785: The Law of Conservation of Mass
1794: executed (guillotine) by revolutionists
1743 – 1794
("The Republic has no use for scientists.“)
Paris News, May 8 1794
http://www.woodrow.org/teachers/ci/1992/Lavoisier.html
http://en.wikipedia.org/wiki/Antoine_Lavoisier
Discovery of photosynthesis: Jan Ingenhousz
born in Breda, Netherlands
court physician to Austrian Empress Maria Theresa
Heard of Priestley’s experiments
Performed >500 experiments
1779: "I observed that plants not only have the faculty to
1730-1799
correct bad air in six to ten days, by growing in it...but
that they perform this important office in a complete
manner in a few hours; that this wonderful operation is
by no means owing to the vegetation of the plant, but to
the influence of light of the sun upon the plant".
Power of plants resides in the influence of sun light!
http://www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm
http://web.lemoyne.edu/~giunta/Ingenhousz.html
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Discovery of photosynthesis: Jean Senebier
1782 experiments:
Leaves submerged in carbonated water produce oxygen
Even ground up leaves produce oxygen
1742–1809
Conclusions:
- photosynthesis absorbs carbon dioxide and generates oxygen
- it occurs in part of the plants that contain green pigment
http://www.aidh.org/Refug/GE_refug/31.htm
Discovery of photosynthesis: Theodore de Saussure
(Swiss chemist)
1804:
gain in weight of a plant is the sum of the
carbon absorbed by the plant in the form
of carbon dioxide and water taken up by
the plant roots and retained as plant
matter.
Conclusion:
- plants convert water, along with carbon
dioxide from the air into dry matter in their
food-making process
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Discovery of photosynthesis: Julius Robert von Mayer
German surgeon, interested in physics
One of the formulators of laws of
thermodynamics: Energy conservation law
1842:
"Nature has put itself the problem of how to catch
in flight light streaming to the Earth and to store
the most elusive of all powers in rigid form. The
plants take in one form of power, light; and
produce another power, chemical difference."
1814-1878
Conclusion:
Plants convert energy of light into chemical energy
http://www.usd.edu/phys/courses/phys300/gallery/clark/vonmayer.html
http://www.cartage.org.lb/en/themes/Biographies/MainBiographies/M/MayerJR/1.html
Discovery of photosynthesis: chlorophyll
1817: French scientists Pelletier and Caventou isolated green
pigment of leaves and called it chlorophyll
chloros - green
phyllon - leave (Greek)
1864: Julius Sachs demonstrated that carbohydrates are produced
in photosynthesis in parts that contain chlorophyll
1883: Theodore Engelman determined that
chlorophylls are key pigments in
green algae, and that red and blue
light were the most active in
generating oxygen
1832-1897
1843-1909
Connection with physics:
Engelman used prism spectrometer
introduced in 19th century and
modified by Bunsen and Kirchhoff
http://www2.nsta.org/energy/find/luminaries/sachs.html
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Discovery of photosynthesis: mechanism
19th century: Photosynthesis converts energy of light into
chemical energy by synthesizing carbohydrates using mostly
water and CO2.
Open question: how can plants do it?
Major advances in understanding photosynthesis (and
biological systems in general) occur when new knowledge and
techniques from other sciences (physics, chemistry…) are
applied to biological systems
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