“Life is bottled sunshine”

Wynwood Reade, Martyrdom of Man, 1924

Photosynthesis – what we know (or should know!!...)

• “Building from light”• Converts carbon dioxide into organic

compounds• Carried out by autotrophs• All life either depends on it directly

as a source of energy, or indirectly as the ultimate source of the energy in their food

• 6CO2 + 6H2O = C6H12O6 + 6O2

So how do we know all this?...

The story starts a long time ago…

• Aristotle (384-322BC)• Greek philosopher• He proposed that

plants, like animals, require food

• He concluded that green plants obtained their nourishment from the soil

• Aristotle’s theory was widely accepted until the 1600’s…

Nicholas of Cusa (1401-1464)

• Cardinal of the Catholic Church

• Philosopher, mathematician, jurist and astronomer

• He planned but never carried out an experiment to determine whether or not plants consume the soil

• He proposed they did not

• Revolutionary!!

Jean Baptiste van Helmont (1579-1644)

• Flemish physician and chemist

• Identified carbon dioxide, carbon monoxide, nitrous oxide and methane

• He was a doctor. He married a wealthy noblewoman and her inheritance enabled him to retire early from medical practice and concentrate on his chemical experiments

• Over 5 years, he carried out experiment originally planned by Nicholas of Cusa and concludes the increase in mass of the plant came from water. He does, however, ignore a slight decrease in soil mass

Robert Hooke • Invented the light

microscope• Observed both plant

and animal cells• ‘Stoma’- from the

Greek word for mouth• First observed by

Malphighi• Stoma were so named

by Heinrich Link because of their appearance

• Their function was unknown to him though

Edme Mariotte (1620-1684)

• French physicist and priest

• In 1660 he discovered the eye’s blind spot!

• In 1676 he hypothesised that plants synthesise their food from air and water

Stephen Hales (1677-1791)

• Physiologist, chemist and inventor

• He studied the roles of air and water and their importance to plant and animal life

• He wrote that plant leaves “very probably“ take in nourishment from the air and that light may also be involved

Charles Bonnet• Observed the emission of

gas bubbles by a submerged illuminated leaf (clearly his pondweed was healthier than the pondweed we have in school!)

Joseph Priestley and his experiments…

• 1733-1804• Theologian, philosopher,

clergyman, scholar and teacher

• One of the scientists credited with discovering "dephlogisticated air“ – oxygen

• Finds out that air which has been made ‘noxious’ by the breathing of animals or burning of a candle can be restored by the presence of a green plant

• Carried out a very famous experiment using bell jars, candles, plants and mice…

Antoine Lavoisier• 1743-1794• Investigated and later

named oxygen• Recognises it is used up

in both combustion and respiration

• His work discredits “phlogiston”, a hypothetical substance previously believed to be emitted during respiration or combustion

• One of the fathers of modern day chemistry

Jan Ingenhousz

• 1730-1799• Physicist, chemist and

plant physiologist• Discovered

photosynthesis (and Brownian motion!)

• Showed that light is essential for photosynthesis and that only the green parts of the plants release oxygen

• 1782 – Jean Senebier demonstrates that green plants take in carbon dioxide from the air and emit oxygen under the influence of sunlight

• 1791 – Comparetti observes green granules in plant tissues, later identified as chlorophyll

Nicolas de Saussure

• 1767-1845• Chemist and plant

physiologist• Proved that the

carbon assimilated from atmospheric carbon dioxide cannot fully account for the increase of dry weight in a plant

• The basic equation for photosynthesis was therefore established

The Biochemistry begins…

• So scientists had now worked out that Carbon Dioxide was taken in and Oxygen was given out, and that the green pigment (named chlorophyll in 1818) played a part in this process, but what actually went on inside the leaf?...

• 1842 – Schleiden states that he believes the water molecule is split during photosynthesis

• 1844 – Hugo von Mohl makes detailed observations about the structure of chloroplasts

• 1845 – Julius Robert von Mayer proposes that the Sun is the source of energy used by living organisms and introduces the concept that photosynthesis converts light energy into chemical energy

• 1862 – Julius von Sachs demonstrates that starch formation in chloroplasts is light dependent

The discoveries continue…

• 1864 – We have the balanced equation for photosynthesis after accurate quantitative measurements of carbon dioxide uptake and oxygen production are made…

6CO2 + 6H2O = C6H12O6 + 6O2

• 1873 – Emil Godlewski proves that atmospheric CO2 is the source of carbon in photosynthesis by showing that starch formation in illuminated leaves depends on the presence of CO2

Not just any old light..

• In 1883, Engelmann illuminated a filamentous alga with light that had been dispersed using a prism

• He discovered that aerobic bacteria in the water all congregated around the portions iluminated with red and blue wavelengths

• This was the first action spectrum!

1905 – Limiting Factors• F.F. Blackman

develops the concept of limiting factors

• He shows that photosynthesis consists of two stages…

• A rapid light dependent process and a slower temperature dependent process

• These become known as the ‘light’ and ‘dark’ reactions

1941 – Ruben and Kaman• They set out to discover

the path of carbon dioxide during photosynthesis but end up discovering something different…

• They experiment using heavy isotopes to discover whether the oxygen produced during photosynthesis comes from the splitting or water or carbon dioxide

• They discover water is split during the first, light-dependent stage of photosynthesis

Daniel Arnon

• 1910-1994• Plant physiologist• 1954 – he demonstrates

light dependent ATP formation in chloroplasts

• 1955 – he demonstrates that isolated chloroplasts are capable of carrying out complete photosynthesis

Melvin Calvin

• Member of the Radiation Laboratory at Berkeley, University of California

• Studied using radioactively labelled carbon dioxide

• 14CO2 fed to Chlorella algae and its path tracked

Melvin Calvin• Melvin Calvin figured out the

steps of the photosynthetic process!

• The Nobel Prize in Chemistry 1961 "for his research on the carbon dioxide assimilation in plants"

Plant biologists are prize winners!

• 1956 – Melvin Calvin and his coworkers are awarded the Nobel Prize in 1961 after they use radioactively labelled CO2 to show the pathway of carbon assimilation during photosynthesis. The second stage of photosynthesis is also known as the Calvin Cycle!

• 1960 – Robert Woodward synthesises chlorophyll and is awarded the Nobel prize in 1965

• 1984 – Deisenhofer, Michel and Huber crystallise the photosynthetic reaction centre from a purple bacterium and use x-ray diffraction techniques to determine its detailed structure. They are awarded the Nobel Prize in 1988.