History of Plants
Over
3,000 million years ago, the first living-organism which resembled a plant
appeared. It was a blue-green algae which lived in the sea and can still be
found in the water today. When the plants made their first appearance on Planet Earth the atmosphere was
unlivable for all oxygen breathing creatures.
The air was made out of carbon dioxide, a gas which to us is deadly. Then
photosynthetic plants came along and slowly over several million years, cleaned
the atmosphere and filled it with oxygen.
If
plants had never come along and revolutionized the atmosphere I don’t think
I’d be writing this. We would never have evolved. To make a long story short, plants could be considered the most precious
living organism on earth.
Discovery
of Photosynthesis
In
1649, Jan Baptista Van Helmont did the first biological experiment in which the
ingredients were measured accurately and all changes noted precisely. Van Helmont
began by transplanting the shoot of a young willow tree into a large bucket of
soil. He weighed the willow and then the soil separately. If the willow tree formed
its tissues by absorbing the nutrients from the soil then the soil should lose
weight as the plant grew. Van Helmont carefully kept the soil covered so that
absolutely nothing could interfere with his experiment.
Naturally,
Van Helmont had to water the willow tree or else it wouldn’t grow. He
concluded that the water he was adding helped carry the nutrients to the tree
and then simply evaporated into the air.
For
five years, Van Helmont waited patiently, watching the tree grow until finally
he removed it from the pot, shook off all the soil and and weighed the plant. In
five years the willow tree had added 164 pounds to its original weight. Then,
for the second part of the experiment, Van Helmont dried and weighed the soil.
Had it lost 164 pounds to the weight of the tree? No. It had only lost 2 ounces!
From
this, Van Helmont concluded that the willow tree drew its nutrients, not from
the soil but from water. Accidentally, he made a mistake and said that the
material that made up the bark, wood, roots and leaves came from the water he
had added over the five years!
The
next big important step in the understanding of photosynthesis came in the early
1770’s. Joseph Preistly, the British man who received the recognition of
discovering oxygen, found that a piece from a mint plants could restore the air
in a container with a burning candle, so that it <the candle> could be
used again. Accidentally, one day, Joseph Preistly placed the candle in a dark
corner of his laboratory. Since the mint plant could not photosynthesize, the
candle’s flame extinguished. Unfortunately,
Mr. Preistly never did really understand that great role which light played in
his experiment.
Several
years later, in 1979, a Dutch physician, Jan Ingenhousz, wanted to find out
whether flowers really did help cure illnesses. After many different tests, he
finally concluded that only the green parts of plants cleaned the air and only
when placed in strong light. Flowers and other non-green parts of plants used up
oxygen just like animals!
In
1796, Ingenhousz suggested that this process of photosynthesis causes carbon
dioxide to split into carbon and oxygen. Then the oxygen is released as a gas.
Later,
other scientists discovered that sugars contain carbon, hydrogen and oxygen
atoms in a ratio of one carbon molecule per molecule of water (CH2O). This is
where the word carbohydrate comes from, carbo-
for “carbon” and hydrate for
“water”. Carbohydrates are a family of chemical compounds including sugars
and starches, which are made up of large numbers of sugar units linked together.
In 1804, the Swiss scientists, Nicholas Theodore de Saussure repeated Van Helmont’s experiment but carefully measured the amounts of carbon dioxide and water that were given to the plant. He showed that the carbon in the plants came from carbon dioxide and the hydrogen from water. Then, forty years later, a Garman scientist, Julius Mayer, showed that the energy of sunlight is captured in photosynthesis.
What
is Photosynthesis?
|
|
Photosynthesis
is basically the conversion of the energy from the sun in to
a usable chemical energy. Only the green parts of the plants are
photoautotrophic because they contain chlorophyll, a green substance found in
chloroplasts. When it was discovered in 1906, chlorophyll was the first molecule
from a living thing to be found that contained magnesium. |
The
basic ingredients for the entire process of photosynthesis, are carbon dioxide,
water, chlorophyll and sunlight.
Here
is the scientific equation of the actions which take place in photoautotrauphs
(living organisms which can perform the photosynthetic reactions):
6CO2
+ 6H2O + (light and chlorophyll) = C6H12O6 + 6O2
In
biochemical terms, this whole equation is simply translated as the reduction of
carbon dioxide into very simple sugars, by hydrogen, obtained by the photolysis
of water, interposed by chlorophyll.
In
English that you could probably understand, it is when carbon dioxide, water and
the energy from sunlight are put together to form sugars and oxygen, which are
let out into the air or kept in the leaves and soon eaten by other living
organisms, like us.
Simple
as it looks, plants are actually a busy factory. The main place for production
are in the leaves, where the most work of photosynthesis are done. Also, there
has to be a way so that the leaves can gather the nutrients, storage areas for
the finished products and ways to get rid of waste products.
Next Section: My Experiment
