The Discovery of Photosynthesis
Jan van Helmont
Joseph Priestly
Jan Ingenhousz
Melvin Calvin & Andrew Benson
Jan van Helmont
Hypothesis: Plants absorb soil particles.
74.47 kg
increase
Adult willow
76.74 kg
young willow
2.27 kg
Held
Constant
5 years
pot + dry soil
90.72 kg
pot + dry soil
90.66 kg
0.06 kg
decrease
Jan van Helmont
van Helmont’s Conclusions:
Plant doesn’t grow mass by absorbing material from the
soil, just from water alone.
Was he correct?
Yes and no!
Jan van Helmont
What important variable did
van Helmont not control for?
Hint: Eliminate H2O and
measure only dry mass: 73.67 kg
(~1 kg less than total mass)
H2O + CO2  Sugar
How could you measure the
effect of CO2 concentrations?
Saussure
Joseph Priestly
Design your experiment:
Joseph Priestly
Think: Priests put candles in churches
CO2 + H2O → Sunlight → C6H12O6 + O₂
Priestly found the plant released OXYGEN from
his experiment keeping mouse and flame alive.
cartoon- sun- m d.png 300
255 pix els
Jan Ingenhousz
1/ 28/ 14 10:22 PM
Think: Light house and Ingenhousz
CO2 + H2O → Sunlight → C6H12O6 + O2
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Ingenhouz repeated Priestly’s experiment but tried it with
and without sunlight to see if that was necessary. He found
sunlight was an important part of photosynthesis.
Jan Ingenhousz
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1/ 28/ 14 10:22 PM
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1/ 28/ 14 10:22 PM
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1/ 28/ 14 10:22 PM
O2 Bubbles
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Green Stems
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Green Leaves
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Brown roots
Quick Review
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1/ 28/ 14 10:22 PM
Reactants:
Light + H2O
Energy
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Products:
+ CO2  Sugar + O2
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Van Helmont
Ingenhousz
Saussure
Priestly
Melvin Calvin
CO2
PGA
PGAL
PGAL
PGAL
PGAL
PGAL
PGAL
Melvin Calvin
http://bcs.whfreeman.com/thelifewire/content/chp08/0802003.html
Melvin Calvin
H2O + CO2  C6H12O6 + O2
Radioactively labeled 14C
PGA
Chromatography
+
X-Ray paper
Melvin Calvin
CO2
1. C02  sugar
2. PGA is the first carbon
compound produced.
PGA
PGAL
PGAL
3. The process is cyclical.
4. PGA is converted to PGAL
with ATP and NADPH.
PGAL
PGAL
PGAL
CO2 + H2O → Sunlight → C6H12O6 + O2
Calvin came up with the Calvin Cycle and showed how plants
take ATP and NADPH to use to make glucose (CO2 →C2H12O6)