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What is the most common biochemical reaction ever?
Well, it may or may not be this one
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That's on every leaf, on every
plant, including all the blades of grass
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Photosynthesis: The Most Important Chemical Reaction for Life on Earth
What do pizza, campfires, dolphins, automobiles, and glaciers have in common?
In the following section, you'll learn that all five rely on photosynthesis, some in
more ways than one
...
Let's delve into how this process
works and why we are so indebted to it
...
These reactions taken as a whole can be
summarized in a single symbolic representation – as shown in the chemical
equation below
...
Then the equation appears
as below
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An arrow indicating the process or chemical change leads from the
reactants to the products, and conditions necessary for the chemical reaction are
written above the arrow
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You use chemical reactions every time you cook or bake
...
A recipe for chocolate chip cookies written in
chemical equation form is shown below
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The equation shows that the “ingredients” for photosynthesis are carbon
dioxide, water, and light energy
...

Of course, light, carbon dioxide, and water mix in the air even without plants
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Necessary conditions include:
1
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chlorophyll - a pigment within plant cells which absorbs light
3
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[Figure 6]
Within plant cells or algal cells, chloroplasts organize the enzymes, chlorophyll,
and accessory pigment molecules necessary for photosynthesis
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Photosynthetic organisms
store the glucose (usually as starch) and release the oxygen gas into the
atmosphere as waste
...


Look closely at its primary purpose: storing energy in the chemical bonds of
food molecules
...
The source of
carbon atoms for the food molecules is carbon dioxide from the air, and the
source of hydrogen atoms is water
...
Light energy is thus transformed into chemical energy, stored
in the bonds which bind six atoms each of carbon and oxygen to twelve atoms
of hydrogen – forming a molecule of glucose
...

One last detail: why do “6”s precede the CO2, H2O, and O2? Look carefully, and
you will see that this “balances” the equation: the numbers of each kind
of atom on each side of the arrow are equal
...


[Figure 8]
The two stages of photosynthesis are the light reactions and the Calvin cycle
...
Since
the Industrial Revolution (late 18th and early 19th centuries), we humans have
relied on products of ancient photosynthesis for enormous quantities
of fossil fuel energy
...
So it may not surprise you that biologists have studied this critical process
in great detail
...
First, the photosynthesis equation summarizes
dozens of individual chemical reactions involving many intermediate
compounds
...
In
the 17th century, people who thought about it at all assumed that plants get their
food from the soil
...

In 1638, Jan Baptist Van Helmont planted a 5 pound willow tree, like the one
shown in Figure below, in a 200 pound tub of soil
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The willow had gained over 160 pounds, but the
soil had lost only 2 ounces
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As you know now, he was half right
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We must excuse him, because no
one in the 17th century knew that carbon atoms form the basis of life, or that
they float around in air in the form of carbon dioxide
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th

In the late 1770s, minister and natural philosopher Joseph Priestley burned a
candle in a jar of air and observed that the candle burned out long before it ran
out of wax
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Priestley suggested that animals, like candles, “injure” the air
...
Only later, after many chemistry
experiments, did Priestley publish his discovery of “dephlogisticated air
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[Figure 10]
Joseph Priestly's bell jar experiment
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Using powerful microscopes, scientists
narrowed the process to one type of organelle within the plant – the chloroplast



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