E. Read the following passage, PHOTOSYNTHETIC
BIOHYBRID SYSTEM and write the paraphrase of each
paragraph after identifying the topic sentences of each one
of them
In the early 1900s, the Italian chemist Giacomo Ciamician
recognized that fossil fuel use was unsustainable. And like many
of today’s environmentalists, he turned to nature for clues on
developing renewable energy solutions, studying the chemistry of
plants and their use of solar energy. He admired their
unparalleled mastery of photochemical synthesis—the way they
use light to synthesize energy from the most fundamental of
substances—and how “they reverse the ordinary process of
combustion.” In photosynthesis, Ciamician realized, lay an
entirely renewable process of energy creation. When sunlight
reaches the surface of a green leaf, it sets off a reaction inside
the leaf. Chloroplasts, energized by the light, trigger the
production of chemical products—essentially sugars—which store
the energy such that the plant can later access it for its biological
needs. It is an entirely renewable process; the plant harvests the
immense and constant supply of solar energy, absorbs carbon
dioxide and water, and releases oxygen. There is no other waste.
If scientists could learn to imitate photosynthesis by providing
concentrated carbon dioxide and suitable catalyzers, they could
create fuels from solar energy. Ciamician was taken by the
seeming simplicity of this solution. Inspired by small successes in
chemical manipulation of plants, he wondered, “does it not seem
that, with well-adapted systems of cultivation and timely
intervention, we may succeed in causing plants to produce, in
quantities much larger than the normal ones, the substances
which are useful to our modern life?”
In 1912, Ciamician sounded the alarm about the unsustainable
use of fossil fuels, and he exhorted the scientific community to
explore artificially recreating photosynthesis. But little was done.
A century later, however, in the midst of a climate crisis, and armed with improved technology and growing scientific
knowledge, his vision reached a major breakthrough.
After more than ten years of research and experimentation,
Peidong Yang, a chemist at UC Berkeley, successfully created the
first photosynthetic biohybrid system (PBS) in April 2015. This
first-generation PBS uses semiconductors and live bacteria to do
the photosynthetic work that real leaves do—absorb solar energy
and create a chemical product using water and carbon dioxide,
while releasing oxygen—but it creates liquid fuels. The process is
called artificial photosynthesis, and if the technology continues to
improve, it may become the future of energy.
How Does This System Work?
Yang’s PBS can be thought of as a synthetic leaf. It is a
one-square-inch tray that contains silicon semiconductors and
living bacteria; what Yang calls a semiconductor-bacteria
interface.
In order to initiate the process of artificial photosynthesis, Yang
dips the tray of materials into water, pumps carbon dioxide into
the water, and shines a solar light on it. As the semiconductors
harvest solar energy, they generate charges to carry out
reactions within the solution. The bacteria take electrons from the
semiconductors and use them to transform, or reduce, carbon
dioxide molecules and create liquid fuels. In the meantime, water
is oxidized on the surface of another semiconductor to release
oxygen. After several hours or several days of this process, the
chemists can collect the product.
With this first-generation system, Yang successfully produced
butanol, acetate, polymers, and pharmaceutical precursors,
fulfilling Ciamician’s once-far-fetched vision of imitating plants to
create the fuels that we need. This PBS achieved a
solar-to-chemical conversion efficiency of 0.38%, which is
comparable to the conversion efficiency in a natural, green leaf.
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