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NOVA - Official Website | Illuminating Photosynthesis

Following photosynthesis, the glucose constructed within plant cells can then be used as a source of energy and materials for cellular activities such as growth, reproduction and the synthesis of more complex materials such as starch, proteins, and fats. The existence of all naturally-occurring molecules (any molecule containing carbon, , and oxygen), and therefore, all sources of energy, can be traced back to the process of photosynthesis. This concept will become very important as we study the flow of energy through ecosystems and the use of energy by humans later in the course.

A leaf may be viewed as a solar collector crammed full of photosynthetic cells

For capturing the sun's copious energy, there are basically two available engineering models: that turn it into flowing electrons or photosynthetic plant cells that turn it into plant food. So which does the job better? After all, such a judgment might help inform policymakers on whether to pursue biofuels or solar electricity.

But the question admits no easy answer, because it begs the deeper question of which one values more: the sheer quantity of electrons produced—so-called efficiency—or the ? After all, storage is a high-value proposition that has made , originally derived from plants, so valuable—cheap, energy dense, easy to transport and storable for later use. That is not the case for electricity from the sun—or any other source—which must be captured the instant it is produced and currently has a limited and expensive option for storage: batteries.

"Chemical fuels [hydrocarbons, like those in oil] would be the game-changer if you could directly make them efficiently from sunlight," notes chemist Nathan Lewis, who directs a lab focused on just that prospect: the U.S. Department of Energy's . "It pairs the biggest source of energy and the biggest storage."

So, a group of 18 biologists, chemists and physicists set out to answer the question by first creating roughly equivalent systems—comparing apples with apples, as it were rather than apples with oranges. Photosynthesis (conducted by ) turns roughly 3 percent of incoming sunlight into organic compounds, including yet more plant cells, annually. ""—comprising a PV cell that provides the electricity to split water into hydrogen and oxygen—turns roughly 10 percent of incoming sunlight into usable hydrogen annually.

That discrepancy suggests there might be room for improvement in photosynthesis, according to the . After all, solar cells are capable of absorbing more of the energy in sunlight because they capture it across the electromagnetic spectrum ranging from infrared to ultraviolet, whereas chlorophyll and other photosynthetic pigments absorb only visual light. Introducing pigments to plants that would help them capture ultraviolet or infrared light could change that equation.

Another idea would be to reconfigure photosynthesis itself. Presently plants employ two systems—dubbed photosystem I and photosystem II—to convert sunlight, CO2 and water into carbohydrates. But both of these photosystems rely on capturing visible light photons, which means the two systems compete for each incoming ray of sunlight. If scientists tweaked the system so that photosystem I relied on visible light but II absorbed, say, ultraviolet light—the efficiency of plants would improve considerably.

"It would be the biological equivalent of a tandem photovoltaic cell," or the stacked photovoltaic cells that absorb different wavelengths of light, says biochemist Robert Blankenship of Washington University in St. Louis, lead author of the analysis. has been demonstrated to convert more than 40 percent of incoming sunlight into electricity, albeit at a prohibitively high price. Such synthetic photosynthetic organism could then become the fuel refinery of the future—a prospect being actively pursued by the Advanced Research Projects Agency–Energy (ARPA–e), a recently formed federal agency tasked with taking scientific findings on alternative energy and turning them into deployable technologies.

At the same time, any biological sunlight-capture method faces one significant constraint—the enhanced bugs or plants have to be kept alive. "We don't want them using those resources to make bugs; we want them to use them to make fuel," explains chemist Eric Toone, ARPA–e's deputy director for technology and program manager for so-called —an effort to harness extremophiles to make fuels for human use—who was not involved in this analysis. "As you tinker with bugs to turn off pathways that aren't doing what you want them to do, you've got to leave the bug capable of staying alive."

Nor did the scientists consider other factors that could diminish the utility of either or both approaches, such as land or water needs, waste, or any of a host of other relevant considerations. For example, the fact that hydrogen fuel-cell cars still cost hundreds of thousands of dollars might overwhelm the usefulness of artificial photosynthesis to produce the lightest element. Still, simply on the basis of converting the most sunlight to usable energy, artificial photosynthesis wins.

But don't count out nature, enhanced or otherwise, yet. After all, plants do several things very well that photovoltaic cells—or artificial photosynthesis systems—do not, such as (382 parts-per-million and rising) directly from the air and use sunlight to turn it into fuel and oxygen.

"Natural photosynthesis turns with lots of carbon-carbon bonds," says chemist Andrew Bocarsly of Princeton University, who was not involved with the analysis. "We've been studying CO2 chemistry for a long time, more than 100 years, and there's very little evidence that we could do what a leaf does."

Of course, plants also have another significant advantage—a bad photosynthetic cell can repair itself; in fact, that's part of its normal operation. No artificial system yet devised—super-efficient or otherwise—can heal itself.

Photosynthesis and plant cells W

The evolution of plants took billions of years to develop an efficient photosynthesis process; creating that synthetic photosynthesis system requires significant research, development and innovation.GCell has succeeded in replicating nature’s photosynthesis with breakthroughs in physics, chemistry, materials science, and nanotechnology to create new business opportunities in indoor and portable energy harvesting product applications where classic silicon-based photovoltaic technologies cannot be used.GCell makes the process of artificial photosynthesis efficient, inexpensive, and robust.

Theprocesses of photosynthesis and respiration take in and release the gasses CO2and O2.Duringphotosynthesis, cells take in release .During respiration, cells take in and release

Photosynthesis without cells: Turning light into fuel

You should be careful to notice that the process of cellular respiration is essentially the reverse of photosynthesis. The catabolic breakdown (burning) of glucose requires the presence of oxygen and yields energy and . This process is generally the same when any organic molecule is respired (or burned) whether it is glucose in a living animal or plant cell, wood in a fire, or gasoline in a car. The breakdown of any energy storing chemical releases carbon dioxide as a byproduct, which may then be used by plants in the photosynthetic process.

Plants get carbon dioxide from the air through their leaves. The carbon dioxide diffuses through small holes in the underside of the leaf called stomata. (singular: stoma. plural: stomata)

The lower part of the leaf has loose-fitting cells, to allow carbon dioxide to reach the other cells in the leaf. This also allows the oxygen produced in photosynthesis to leave the leaf easily.




Carbon dioxide is present in the air we breathe, at very low concentrations. Even though it forms about .04% of the air, it is a needed factor in light-independent photosynthesis.

In higher concentrations, more carbon is incorporated into carbohydrate, therefore increasing the rate of photosynthesis in light-independent reactions.

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photosynthesis cells plant Study Sets and Flashcards | Quizlet

This process is extremely important for life on earth as it provides the oxygen that all other life depends on.


Just like humans and other living things, plants also need this food for many things. Let's see a few:

Glucose resulting from photosynthesis is used during respiration to release energy that the plant needs for other life processes.

The plant cells also convert some of the glucose into starch for storage. This can then be used when the plant needs them. This is why dead plants are used as biomass, because they have stored chemical energy in them)

Glucose is also needed to make other chemicals such as proteins, fats and plant sugars that are all needed for the plant to carry out essential growth and other life processes.

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