Photosynthesis - Shmoop Introduction

To a plant, sunbathing is life. Literally. In fact, plants have evolved all sorts of ways to maximize their exposure to the sun while at the same time preventing loss of critically needed water. Plants, as well as some algae and bacteria, perform photosynthesis, a process that involves the capture and use of the Sun’s energy to create biological compounds. Photosynthetic organisms generate these compounds using carbon dioxide (CO₂) and water (H₂O), and the products they release are oxygen (O₂) and carbohydrates as byproducts.

Plants provide us with the oxygen we breathe. Now that you know this tidbit of info, you may have a little better understanding of why environmentalists freak out over the rapid destruction of rainforests, wetlands, and natural habitat. The lower the number of plants on the planet, the less O₂ produced for important things like, say…breathing.

Photosynthesis can be divided into two processes: the first requires light, and the second does not.

In the first phase of photosynthesis, cellular protein pigments called chloroplasts are excited by light that propels them into high-energy states. The chloroplasts then transfer this energy through electrons to other protein complexes (read: several proteins stuck together). This group of proteins is called the electron transport chain. The proteins operate similarly to a group of dominoes: after the first one has been pushed, each protein transfers energy to each member along down the line.

Water (H₂O) is split in this process, releasing oxygen (O₂) and hydrogen ions (H⁺). The electrons from the electron transport chain combine with these H⁺ ions and nicotinamide adenine dinucleotide phosphate ions (NADP⁺) to form adenosine triphosphate (ATP) and a reduced unit of NADP⁺, called NADPH (NADP plus an electron, or H). These energy storage forms, ATP and NADPH, are used to convert carbon dioxide (CO₂) to build carbohydrates during the second phase of photosynthesis. Plants can then break down these carbohydrates to fuel their existence.

Are you jealous of your green friends? It must be nice to sunbathe all day long. Before you become plant-green with envy (sorry…), remember that plants do not have the ability to eat milkshakes or French fries, and they can't ride a bike along the beach. Does that give you some satisfaction? Good.

And, once you master your knowledge of photosynthesis, you can relax in the sun with a greater appreciation for the O₂ you breathe, knowing that it is produced from the photosynthetic process. Don’t forget the sunscreen—at least SPF 30—you aren’t a plant, after all. Finally, you will realize that the beachside smoothie you are sipping, along with everything else that you have ever eaten, or will ever eat, relies on photosynthesis either directly or indirectly as its source of energy. Unless, of course, you have gotten into the habit of snacking on chemoautotrophs that live in rocks or deep-sea hydrothermal vents. They don't use photosynthesis.