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Power Plants

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Throughout history many cultures have worshiped the Sun for its life-giving powers. In reality it is not the Sun itself, but rather the plants that have learned to harvest that all powerful sunshine, to whom we should bow on bended knees.

Think about it. Everything you have ever eaten, or will ever eat, can ultimately be traced back to an organism carrying out photosynthesis. The word itself, “Photosynthesis” says it all: “To create from light.” And the precious oxygen we breathe is one of the waste products of that creation.

The oldest known fossils are those of cyanobacteria, microscopic organisms that 3.5 billion years ago evolved the ability to turn water, carbon dioxide and sunlight into sugar, that magic molecule that fuels all cellular life. Through a fateful encounter with a different and more complex cell, cyanobacteria eventually gave rise to the ancestor of those organisms today known as plants. Today those remnant cyanobacteria are known as chloroplasts.

Most people know that plants take in water and CO2 and produce carbohydrates and gaseous oxygen. But what is often misunderstood is the source of those oxygen molecules. They come from the splitting of water, not the CO2.

The first step in photosynthesis uses the energy of sunlight to break a water molecule into its basic parts; an atom of oxygen and two atoms of hydrogen. Known as “photosystem II” (named that way because it was discovered after the second step in the process, photosystem I) the hydrogen protons are stripped away from a water molecule and two atoms of oxygen are joined together released as a waste product.

As positively charged protons accumulate on one side of a membrane a sort of chemical battery is created, the power of which is then used to generate the energy-rich molecule ATP which in turn is used to fix CO2 into the sugars that feed almost all life on the planet.

Ramaraja Ramasamy,right, and Yogeswaran Umasankar work together to capture energy created during photosynthesis. Ramasamy is an assistant professor in the UGA College of Engineering and Umasankar is postdoctoral research associate working in his lab.

Ramaraja Ramasamy,right, and Yogeswaran Umasankar work together to capture energy created during photosynthesis. Ramasamy is an assistant professor in the UGA College of Engineering and Umasankar is postdoctoral research associate working in his lab.

Now researchers at the University of Georgia have figured out a way to tap into these most ancient of power plants. By coupling the isolated chloroplast membranes from a spinach plant onto carbon nanotubes Ramaraja Ramasamy and colleagues have succeeded in generating a small electrical current when light strikes the sample.

The ability to generate electricity by recombining the hydrogen and oxygen atoms from a split molecule of water has been around for a long time. Known as fuel cells these power stations have been used by NASA for decades to power space craft. They are also employed as back up emergency generators or in places that are off the grid but still require electricity. Most researchers who looked to green plants to power our future economy focused on harvesting the hydrogen atoms that are created when photosynthesis splits water and then recombining these atoms in a fuel cell; creating electricity with water as the only waste product.

Ramaraja Ramasamy

Ramaraja Ramasamy

Dr. Ramasamy’s device gets around this whole problem by generating electricity directly from the plant material itself. He says "We have developed a way to interrupt photosynthesis so that we can capture the electrons before the plant uses them to make these sugars."

At the moment the amount of electricity generated in this way remains tiny, but the potential is huge. Powering our nation’s cities and factories from plant chloroplasts is not something that is going to happen anytime soon but in the near future this technology may enable power generation in remote or isolated places in which even a small amount of electricity is enough to make a difference.

Three and a half billion years ago algae, with their ability to harvest the near limitless amount of sunlight, forever changed the course of life on the planet. They may be poised to do it again.

Images: Image 1; Image 2; Images 3 and 4.

The views expressed are those of the author and are not necessarily those of Scientific American.

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