Video Transcript
Melvin Calvin investigated
photosynthesis in algae. The diagram demonstrates a
simplified outline of his experiment. Why is the algae subjected to a
quick flash of light? (A) To initiate cell division. (B) To stop respiration. (C) To initiate photosynthesis. (D) To begin digestion. (E) To kill the cells.
During photosynthesis, plants
convert carbon dioxide and water into glucose and oxygen using light energy. Without light energy, the reactions
of photosynthesis cannot proceed.
Melvin Calvin was an American
biochemist who was studying photosynthesis in the 1940s. Calvin used different isotopes of
carbon in his work. So let’s ensure that we understand
what isotopes are before we look at his experiment.
Isotopes are atoms of the same
element that have the same number of protons but different numbers of neutrons. The most common isotope of carbon
is carbon-12, which has six protons and six neutrons. Carbon-14 is a different isotope of
carbon that has six protons and eight neutrons. Carbon-14 is radioactive and can
therefore be tracked at experiments, like the one carried out by Calvin.
Let’s take a closer look at
Calvin’s experiment into photosynthesis. In the flask, there is a population
of Chlorella algae. These algae were provided with
carbon dioxide which contained the carbon-14 isotope. The algae was then exposed to a
quick flash of light to initiate photosynthesis. Then they were quickly dropped in a
beaker of hot alcohol to stop photosynthesis.
By studying the algae, Calvin
discovered that even after a very quick flash of light, a three-carbon compound was
formed. This three-carbon compound is known
as phosphoglyceraldehyde, or PGAL. PGAL can be used to produce a range
of other organic compounds essential for an organism’s survival, such as glucose,
proteins, and fats.
Melvin Calvin’s work was so
important that you will often see the light-independent reactions of photosynthesis
referred to as the Calvin cycle.
Using what we now know about
Calvin’s experiments, let’s take a look back at the question. The correct answer is option
(C). In Calvin’s experiment, the algae
is subjected to a quick flash of light to initiate photosynthesis.
