the log blog

Wouldn’t it be great to be able to conjure your favorite food out of thin air? Plants accomplish this seemingly miraculous feat every day. They are able to feed themselves using a technique called photosynthesis. Instead of having to search for food, they create all of the food energy they need from sunlight, air and water.

How does this amazing process work? Here is the chemical equation for photosynthesis: 6CO2 + 6H2O (+ light) -> C6H12O6 + 6O2

For those of us who slept through high school chemistry class, this equation can be translated into English as follows: 6 molecules of carbon dioxide plus 6 molecules of water plus light converts to one molecule of sugar and 6 molecules of oxygen.

The majority of the energy a plant manufactures is produced in the leaves. The carbon dioxide part of the equation is obtained through the air, while the water is brought up to the leaves by the roots of the plant. In order to control water loss, the leaves are covered by a thick skin called the epidermis. Carbon dioxide and oxygen are only able to pass in and out through tiny pores called stomata, which the plant can open and close as needed. In order to capture the energy in sunlight, leaves contain special cells called chloroplasts, which contain high concentrations of the pigment chlorophyll. Chlorophyll absorbs blue and red light, reflecting back yellow and green. This is why plants appear green to us-green light is reflected back into our eyes because it is the only wavelength of light that the plant does not absorb. In order to catch as much sunlight as possible, many plants use more than one type of chlorophyll and also other secondary pigments such as carotenoids.

The chlorophyll molecules first convert sunlight into a chemical form of energy called adenosine triphosphate, or ATP for short. This is called the “light reaction,” because it has to happen in sunlight. The next phase of photosynthesis is called the “dark reaction,” because it does not require the presence of sunlight to be completed. The “dark reaction” uses a process called the Calvin cycle to produce sugar from ATP and carbon dioxide. The sugar is stored and provides energy and nourishment for the plant.

The dark reaction can happen in 3 different ways, depending on the environmental conditions that the plant has evolved to survive in. For example, plants that live in temperate climates (called C3 plants) use pure, unaltered carbon dioxide in the Calvin cycle. This works fine as long as the weather is cool enough that the plant can open its stomata without losing too much water. In hotter, drier conditions, the plant has to leave its stomata closed for most of the day. Some plants, called C4 plants, solve this problem by converting carbon dioxide into oxaloacetate first, which makes photosynthesis possible even with low levels of carbon dioxide in the leaves. Desert plants cannot open their stomata during the day at all-they turn carbon dioxide into a variety of organic compounds at night when it’s cool. During the day, they break down these compounds and free up the carbon dioxide for use in the Calvin cycle. These plants are called CAM plants.

Once the carbon dioxide has been broken down and turned into sugar, the remaining oxygen is allowed to flow out of the stomata and into the surrounding air. Plants don’t actually “breathe in carbon dioxide and breathe out oxygen” as many people believe. Plant respiration is different than photosynthesis-plants “breathe” in oxygen and use it to break down the sugars produced by photosynthesis. However, the carbon dioxide that plants “exhale” is easily used up during photosynthesis. Plants use more carbon dioxide than they send out and send out far more oxygen than they consume.

Photosynthesis is one of the most important of all natural processes. In fact, almost all of the oxygen in the atmosphere today was produced through photosynthesis. If it were not for plants, the earth would be uninhabitable for “higher mammals” like us. We would not exist at all if plants had not evolved first. Using photosynthesis, plants make the air breathable and break down carbon dioxide, which is greenhouse gas that contributes to global warming.

Additionally, photosynthesis does not produce food only for plants-it produces food for all living things on the planet. Only organisms that are photosynthetic are capable of turning sunlight into usable energy-every other creature on Earth has to consume the energy that plants produce in order to survive. Even animals that are carnivorous are ultimately dependent on plants for survival, because the energy they get from their prey comes from plants.

So, with that in mind… Have you hugged a tree today?