Plants Essay

This essay has a total of 792 words and 4 pages.

plants



Have you ever wondered why your plants in your house and outside lean towards the sun. In
my project I hope to answer why this happens. I am going to be using lima beans to do
this with. The Greek philosopher Aristotle may have been the first to attempt to explain
the processes of photosynthesis and food production. He believed that plants could obtain
from the soil all the components required for growth. The cycle was completed when
organisms perished and became reincorporated into the soil.

This view was not seriously challenged until the 17th century with the experiments of
Joannes Baptista van Helmont, a Flemish physician. He carefully measured the weight
increase of a willow planted in soil, to which he periodically added only rainwater. The
plant increased in weight by 77 kg (169 lb), and the soil decreased in weight by 57 gm (2
oz). He concluded that it was water, and not substances in the soil, that provided plants
with their growth material. Later, in the early 18th century, Stephen Hales conjectured
that light and air might be significant factors in the growth of plants.

The classical experiments of Joseph Priestley laid the foundations of the modern
photosynthetic theory. He found that the composition of air inside a closed glass
container changed after a candle had burned in it or after a small animal had breathed in
it. This air then was unable to support further burning or breathing. He proposed that
this "fixed air" contained "phlogistic matter"—later found to be carbon dioxide—that could
be "dephlogisticated" by plants. Although his interpretation was wrong, he had discovered
that plants use a component of the atmosphere in their life processes.

Jan Ingen-Housz in 1779 and Jean Senebier in 1796 refined Priestley's ideas. They observed
that plants could restore the "fixed air" only in the presence of light; the plants made
the air noxious if kept in darkness. The role of light in photosynthesis thus was firmly
established. Antoine Laurent Lavoisier had previously described the chemical composition
of air; his findings led Ingen-Housz to recognize that plants utilize carbon dioxide to
obtain carbon in order to build organic molecules and that they release oxygen into the
atmosphere. That plants need water in the process was demonstrated by careful quantitative
experiments of Nicolas Th odore de Saussure. With the formulation of the theory of energy
conservation in 1845 by Julius Robert Mayer, the function of light as the energy source
for the photosynthetic process began to be understood, and the basic elements of the
photosynthesis were established.

George G. Stokes and Henry C. Sorby first described the chemical structure of the green,
light-absorbing pigment chlorophyll. By 1913, Richard Willstatter and A. Stoll had
published the empirical formulas of the two major forms, chlorophylls a and b. They
hypothesized that the chlorophyll itself combined with carbon dioxide and water and that
light decomposed the complex into oxygen and formaldehyde. This theory was superseded in
the 1920s, when Otto H. Warburg and Warbus Negelein demonstrated that the photosynthetic
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