Download Photosynthesis - Historial Perspective - CIA-Biology-2011-2012

A Historical Perspective of
Photosynthesis
Is this always the way
photosynthesis has been
understood?
Aristotle – 350 BC
“Green plants
obtain their
nourishment
from the soil.
Leaves are
mere ‘shading
devices’ that
provide a level
of comfort for
the roots.”
Jan Baptista van Helmont (1643)
He performed the classic ‘willow tree experiment’
He studied plant growth by weighing a small
tree, some soil, and a pot. Then he planted
the small tree in the dirt (in the pot).
He watered the tree regularly  after several
years, he removed the tree and reweighed
the tree, soil, and pot.
What did he discover?
1. The weight of the pot did not change.
2. The weight of the soil decreased. (very small
change - lost several ounces from 200 lbs)
3. The weight of the tree increased. (very large
change – gained 165 pounds)
What did he conclude?
Plants only need water to grow. (We now
know that plants also need CO2 – in 1600,
no one had any idea of what air consisted of,
let alone any way to measure the weight of
gases…
Joseph Priestly (1771)
He performed the classic ‘bell jar’
experiments.
He observed that when lit candles are
placed in a closed container, they soon
go out…
But, if a living plant was put in the container,
the candle would stay lit longer…
He was the first person to show that plants
produce oxygen gas.
For this discovery, the King of England
awarded him a medal as he exclaimed –
“We are assured that no vegetable grows
in vain…but cleanses and purifies our
atmosphere!”
He confirmed his findings by showing that a
mouse will live considerable longer in a
bell jar with a plant than without a
plant…(and the plant will live longer as
well…)
Joseph Priestly Experiments
Jan Ingenhousz (1779)
He was a trained doctor
from Holland.
He finds that aquatic plants
produce oxygen bubbles
in the light but not in the
dark.
He concludes that plants
need sunlight to produce
oxygen.
T.W. Engelmann (1843-1909)
German Botanist – Built and developed the ideas of
Ingenhousz in more depth.
In 1883, he used an alga that has long spiral
chloroplasts. (Spirogyra)
He illuminated the alga with light shown through a
prism  He placed oxygen loving bacteria on
the alga. He proposed that oxygen production
would be the greatest in regions where light of a
given color was absorbed the most. He
therefore expected to see the most bacteria in
those regions.
The bacteria were most concentrated where red
light fell, and also where blue light fell.
He concluded that plants absorb the light they
need (red and blue) and reflect the rest (green)
Wavelengths of light that are used
by plants
Melvin Calvin (1948)
• Traces the chemical pathway that carbon
follows to form glucose. (Calvin Cycle)
Rudolph Marcus (1992)
• Wins the Nobel Prize in Chemistry for
describing the process by which electrons
are transferred from one molecule to
another in the electron transport chain.
So, what do we know today
photosynthesis to be?...
Light, water, and carbon dioxide are used to
make sugar (usually glucose). As byproducts, oxygen gas and a small bit of
water are also produced…
CO2 + H2O + light energy  CH2O + O2 + H2O
Photosynthesis is when light energy is changed to
chemical energy which is stored in glucose
molecules…(remember the whole usable vs.
unusable relationship?)
unusable
usable
[light -------------------------- glucose ------------------------- ATP]