Things Fall Apart-Part 2 Green Genius

But how is light fuel? We can bathe in the Sun all we want, but we have no way to convert its light into the chemical energy that our cells can use. We can change it into electrical energy with a solar panel, but that’s not going to feed our cells. Lie on the beach all day, and you are still going to have to eat lunch. How does the Sun become lunch?

We are completely dependent on plants to convert sunlight into a currency that our cells can spend. Without plants, our lives would be impossible and the world would be populated, as it was for several billion years, by bacteria alone. Light energy from the Sun is captured by the green genius of plants, and converted to a form usable by cells. How do they do it?

What plants do, through the process of photosynthesis, is to convert light energy to chemical energy. The plant uses the Sun’s light to form new molecules that store chemical energy in the bonds between their atoms. These bonds can later be broken and their energy released and used by the plant itself or by something that eats the plant.

Plants capture sunlight in their leaves using a pigment (which is simply a molecule that absorbs light). The cells that make up the leaves of plants are filled with the pigment chlorophyll. Chlorophyll absorbs light of a certain wavelength, and is notably poor at absorbing in the green range, leaving that green light to bounce off and into our eyes, and thereby lending leaves their green color. The energy from the Sun’s light excites an electron in the chlorophyll molecule. It can be thought of as the electron being knocked up a hill. Through a complicated set of reactions called electron transport, as the electron falls back downhill to a lower energy state, the attendant release of energy is harnessed, like falling water turning a wheel at a mill.

But chlorophyll has lost an electron which needs to be replenished in order for the system to be sustainable. Where can the plant find a nice ready source of electrons to replace the one lost from its chlorophyll? Water. The plant strips an electron from water to reconstitute the chlorophyll molecule. In the process, the plant creates a very notable waste product: oxygen gas.

So the plants have harnessed some energy from sunlight, but how do we use it? Plants take carbon dioxide from the air, and utilizing the energy from sunlight, link its carbon atoms together into chains. The Sun’s energy is now stored in the chemical bonds between the carbon atoms, and if the bonds are broken, the energy is released to fuel cellular activities. These new storage molecules are sugars, which are simply long chains of these carbon atoms. The sugars can be combined into larger storage forms like starches, and structural elements of plants like cellulose.

So plants take energy from the Sun, carbon dioxide from the air, and in the presence of water, create high energy carbohydrate molecules and oxygen gas. We can now eat the plant directly and release the energy stored in the carbohydrate bonds, or indirectly by eating the flesh of animals who have eaten plants. Our ability to utilize this energy source also involves carbon dioxide and oxygen, and in a way that highlights a true planetary harmony.

The molecules we absorb from our ingestion of plants (or animals which have themselves eaten plants) are broken down and sent to our cells where the bonds holding the molecules together are broken. Their energy is released in a combustion reaction–like any other in a car engine or a bonfire. As in all combustion, oxygen is required for the reaction to occur, and carbon dioxide is released as a waste product.

Our lungs absorb the oxygen we require and release the carbon dioxide we create. Walk faster, muscle cells work harder, need more energy, burn more molecules, require more oxygen, create more carbon dioxide, we breath harder. Meanwhile, the plants are breathing in our carbon dioxide waste and breathing out oxygen.

So plants capture the energy from sunlight, take carbon out of the air and make it useable as the key ingredient for all other multicellular life forms, provide the oxygen we breathe, and process our carbon dioxide waste. But what have they done for us lately?

Plants provide all our energy. That energy allows us to maintain our state of order and complexity, to oppose the universal tendency to disintegration. So, indeed life without plants, without energy is impossible. But there is one more ingredient that, along with energy, allows our unlikely existence: information.

Energy and information. The blueprints for our existence reside in the DNA code. How this information organizes the mishmash–of molecules and atoms, carbon and nitrogen, bits of metal and minerals–we take in through our mouths to manifest an unfathomably complicated, functional organism is where we turn next.