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PhotosynthesisSci 190 ELecture 13

photo-synthesis – building by light

CO2 + H2O (CH2O) + O2light

PlantsAlgaeBacteria

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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

4.27 × 10171.08 × 1017Total

0.28 × 10170.01 × 1017Hydroelectric

0.28 × 10170.03 × 1017Nuclear electric

0.03 × 10170.003×1017Geo, solar, wind…

1.03 × 10170.25 × 1017Coal

1.00 × 10170.24 × 1017Gas

1.62 × 10170.45 × 1017Petroleum

World (kJ)US (kJ)Year 2002

http://www.eia.doe.gov/iea/overview.htmlhttp://www.cslforum.org/usa.htm

~1/3 of totalphotosynthesis(1018 kJ)

Sunlight falling on Earth surface is ~4 ×1021 kJ/year(~1 kW/m2)

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Carbon dioxide emission

Using gas, coal, oil as energy source reverses natural process, burns oxygen and emits CO2 (‘green house effect’)

All of oxygen in the atmosphere was produced by photosynthesis!

Photosynthesis annually fixes ~ 1011 tons of carbon

Year 2002Carbon emission:

USA 1.6 × 109 tonWorld 7 × 109 ton

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

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169 lb

200 lb - 2 ounces of dry soil

Discovery of photosynthesis: van Helmont

http://mattson.creighton.edu/History_Gas_Chemistry/vanHelmont.html

1579-1644

Joean Baptista van Helmont

Belgian physicianPioneer chemist

“Willow” experiment:

200 lb of dry soil

5 lb

rainwater only5 years

Conclusion: 164 pounds of wood, bark, and roots, arose out of water only.

Discovery of photosynthesis: van Helmont

1579-1644

Joean Baptista van Helmont

http://www.howe.k12.ok.us/~jimaskew/botzo/botphoto.htm

Hypothesis: Water is the only nutrient for plant growth

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Discovery of photosynthesis: John Woodward

1665 - 1728

Physician and geologist, Cambridge University

http://www2.nsta.org/Energy/find/primer/primer2_5.html

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!

Discovery of photosynthesis: Microscope

Progress relies on experimental methodsEnd of the 17th century: invention of microscope

Robert Hooke

1635-1703

1665: Published “Micrographia”Hooke’s microscope

drawing of cells in cork

Hooke was the first to observe cells

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Discovery of photosynthesis: Microscope

Anton Van Leeuwenhoek

1632-1723

Improvement of a microscope

Focus knob

Sample translator

Sample holder

Lens

270x magnification!

Discovery of photosynthesis: Nehemiah Grew

1641 - 1712

English botanist

microscopic studies of the internal structure of plants in the 1670's:Leaves have many openings

“[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

1677–1761

English physiologist, chemist“Father” of plant physiology

http://www.hcs.ohio-state.edu/hort/history/108.html

“the leaves and stems of plants do imbibe elastic air”

mercury

water

1727: published “Vegetable Staticks”

Was able to measure the ‘sucking’ power of plants

Discovery of photosynthesis: J. Priestley

1733 – 1804

Joseph Priestley • Never took any science course

• Minister in a small church in Leeds

• 1766: met Benjamin Franklin in Londonbecame interested in science

• 1767: graphite conducts electricitypublished “The history of electricity”

• 1770: eraser

• 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 ofall 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

27 days

4. Mouse and mint plant 5. Mouse needs plantPlant needs mouse

3. Candle and mint plant

Priestley’s conclusions

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

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

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Discovery of photosynthesis: Antoine Lavoisier

1743 – 1794

http://en.wikipedia.org/wiki/Antoine_Lavoisier

Wealthy family

1773: Repeated Priestley’s experimentsBurning = combining with oxygen!

1783: Proved phlogiston theory to be wrong1785: The Law of Conservation of Mass

named in 1779‘acid-former’

1794: executed (guillotine) by revolutionists("The Republic has no use for scientists.“)Paris News, May 8 1794http://www.woodrow.org/teachers/ci/1992/Lavoisier.html

Discovery of photosynthesis: Jan Ingenhousz

1730-1799

born in Breda, Netherlands court physician to Austrian Empress Maria Theresa

Heard of Priestley’s experimentsPerformed >500 experiments

1779: "I observed that plants not only have the faculty to 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

1742–1809

http://www.aidh.org/Refug/GE_refug/31.htm

1782 experiments: Leaves submerged in carbonated water produce oxygenEven ground up leaves produce oxygen

Conclusions:- photosynthesis absorbs carbon dioxide and generates oxygen- it occurs in part of the plants that contain green pigment

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

http://www.usd.edu/phys/courses/phys300/gallery/clark/vonmayer.htmlhttp://www.cartage.org.lb/en/themes/Biographies/MainBiographies/M/MayerJR/1.html

1814-1878

German surgeon, interested in physics

One of the formulators of laws of thermodynamics: Energy conservation law1842: "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."

Conclusion:Plants convert energy of light into chemical energy

Discovery of photosynthesis: chlorophyll1817: French scientists Pelletier and Caventou isolated green pigment of leaves and called it chlorophyll chloros - green

phyllon - leave (Greek)

1832-1897

1864: Julius Sachs demonstrated that carbohydrates are produced in photosynthesis in parts that contain chlorophyll

http://www2.nsta.org/energy/find/luminaries/sachs.html

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

1843-1909

Connection with physics: Engelman used prism spectrometer introduced in 19th century and modified by Bunsen and Kirchhoff

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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