Download Discovery of Photosynthesis

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Discovery of Photosynthesis
DIRECTIONS. Many scientists contributed to the discovery of photosynthesis. Read the following
passage about the discovery of photosynthesis & create a timeline in the chart that follows.
The discovery of photosynthesis cannot be attributed to one scientist’s experiments. Rather,
several scientists have performed experiments that have led to our current understanding of
photosynthesis. The contributions of 5 of these scientists are described below.
In 1643, Jan Baptista Van Helmont did the first
biological experiment in which all ingredients were measured
accurately and all changes noted precisely. From his
experiment, Van Helmont concluded that a willow tree drew
its nutrients, not from the soil, but from water. He was
mistaken in concluding the material that made up the bark,
wood, roots and leaves came from the water he had added
over the five years. It wouldn’t be until the 1800s that it was
correctly understood where the mass of a tree came from.
The next important step in the understanding of
photosynthesis came in the early 1770’s. Joseph Priestly, the British man recognized for discovering
oxygen in 1774, discovered that when he placed a candle in an enclosed jar, the candle would burn out
very quickly, much before it ran out of wax. He called the air inside the jar “injured.” He further
discovered that a mouse could similarly "injure" air. He
then showed that the “injured" could be restored by a
plant. One day , Priestly accidentally placed the jar
with the candle and plant in a dark corner of his
laboratory. The candle’s flame extinguished, but
Priestly never explored the role that light played in his
observation.
In 1778, Dutchman Jan Ingenhousz, court
physician to the Austrian Empress, repeated Priestley's
experiments (with a few alterations). It had been noticed
that submerged plants gave off small bubbles and, if the
plants were placed in the shade, these bubbles eventually
stopped. Ingenhousz carried out a series of experiments
to prove that the bubbles were independent of heat and
that the cause of this phenomenon must be light. He further discovered that the accumulated gas re-lit a
glowing splint, suggesting that the air was full of oxygen. In the dark, however, he found that the plants
gave out less gas, but that the gas extinguished a flame, meaning that
the air lacked oxygen. Ingenhousz concluded that in light plants
produced oxygen, but in the dark they did not.
In 1796, Jean Senebier, a French pastor, showed that the
"injured" air was carbon dioxide and that it was taken up by plants
during photosynthesis. Senebier demonstrated that light is the agent
responsible for the fixation of carbon dioxide and that oxygen is
liberated only in the presence of carbon dioxide. In 1804, 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. Saussure showed that the increase in mass of
the plant as it grows could not be due only to uptake of water (as van
Helmont concluded), but also to the incorporation of carbon dioxide.
These 5 scientists, though not the only to contribute to the discovery of photosynthesis, were
instrumental in discovering the major reactants and products of photosynthesis. Their conclusions
provided the basis for all further photosynthesis studies.
Discovery of Photosynthesis TIMELINE
Year
Scientist (last name)
Contribution to Photosynthesis