Download Life is bottled sunshine

“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, lightdependent 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.