The Discovery of Photosynthesis

Jan van Helmont

Joseph Priestly

Jan Ingenhousz

Melvin Calvin & Andrew Benson

pot + dry soil 90.72 kg

pot + dry soil 90.66 kg

0.06 kg decrease

young willow 2.27 kg

Adult willow 76.74 kg

74.47 kg increase

Held Constant

5 years

Jan van Helmont

Hypothesis: Plants absorb soil particles.

Jan van Helmont

van Helmont’s Conclusions:

Was he correct?

Yes and no!

Plant doesn’t grow mass by absorbing material from the soil, just from water alone.

Jan van Helmont

Hint: Eliminate H2O and measure only dry mass: 73.67 kg (~1 kg less than total mass)

What important variable did van Helmont not control for?

H2O + CO2 Sugar

How could you measure the effect of CO2 concentrations?

Saussure

Joseph Priestly

Design your experiment:

Joseph Priestly

Priestly found the plant released OXYGEN from

his experiment keeping mouse and flame alive.

CO2 + H2O → Sunlight → C6H12O6 + O₂

Think: Priests put candles in churches

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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.

CO2 + H2O → Sunlight → C6H12O6 + O2

Think: Light house and Ingenhousz

Jan Ingenhousz

Green Stems Green Leaves Brown roots

O2 Bubbles

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Quick Review

+ H2O CO2 Sugar O2 +

Products: Reactants:

Saussure

Van Helmont

Ingenhousz

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Light Energy

Priestly

+

Melvin Calvin

CO2

PGA

PGAL PGAL

PGAL

PGAL

PGAL

PGAL

Melvin Calvin

http://bcs.whfreeman.com/thelifewire/content/chp08/0802003.html

PGA

H2O + CO2 C6H12O6 + O2

Radioactively labeled 14C

Chromatography +

X-Ray paper

Melvin Calvin

Melvin Calvin

CO2

PGA

PGAL

PGAL

PGAL

PGAL

PGAL

Calvin came up with the Calvin Cycle and showed how plants

take ATP and NADPH to use to make glucose (CO2 →C2H12O6)

CO2 + H2O → Sunlight → C6H12O6 + O2

2. PGA is the first carbon compound produced.

3. The process is cyclical.

4. PGA is converted to PGAL with ATP and NADPH.

1. C02 sugar