Recently in class, we have started talking in depth about the process of photosynthesis in plants. Photosynthesis is the process in which photosynthetic organisms such as plants and some other types of living organisms capture light energy from the sun and use it to convert water and carbon dioxide into oxygen and chemical energy in the form of the organic compound glucose. Many autotrophs, such as plants, use this process to create food for themselves. Photosynthesis is important to all of life, as not only do organisms that are consumers indirectly depend on the energy that these autotrophs produce, but also the oxygen produced as a byproduct of photosynthesis sustains the majority of life on Earth. As most of Earth’s living organisms have evolved to require oxygen for cellular processes, most organic matter (food) would cease to exist, as would most living organisms, and eventually even the entire atmosphere would lack oxygen. The reliance on oxygen that life has on Earth shows the importance of plants in sustaining ecosystems across the planet.
However, despite being the most well-known photo-synthesizers, plants are not the only photosynthetic organisms on Earth. Similar to how many plants help sustain life on land, phytoplankton- a category that includes single-celled plants, bacteria, algae, and other microscopic protists- are the photosynthetic organisms that help sustain life in the ocean. In addition, algae is also an essential group of photosynthetic protists in water ecosystems. Surprisingly, in rare cases, even some animals can photosynthesize. For example, the Emerald Sea Slug obtains the genes and chloroplasts from the algae that it consumes, eventually accumulating and allowing it to photosynthesize. Though technically not the same process as photosynthesis as we know it in plants, the insect Pea Aphid also has a sunlight-harvesting mechanism as it uses light energy from the sun to produce ATP. Even the Spotted Salamander, a vertebrate, surprisingly acquires photosynthetic genes from the algae it eats, which is rare considering that most vertebrates have immune system components in their spines that kill foreign substances such as algae. However, most animals have not evolved to be photosynthetic, possibly due to the disadvantages as the dangers of exposure to UV light, the conflict of a large surface area with other evolutionary adaptations that are survival strategies, and health concerns with sugar rich diets. One interesting photosynthetic organism is not a plant, protist, or animal. Cyanobacteria are microscopic bacteria in water, and are one of the oldest organisms on earth, and believed to be the first photosynthetic organisms. In fact, it is believed that photosynthesis evolved in plant cells and other organisms because of cyanobacteria being ancestors of modern chloroplasts, as plant cells engulfed cyanobacteria and started an endosymbiotic relationship with them. It is in cyanobacteria that recently an important discovery was made.
Recently, scientists discovered an entirely new type of photosynthesis. The majority of photosynthetic organisms on earth use red visible light for photosynthesis; however, recent studies of cyanobacteria show that this new type uses near-IR radiation. The photosynthesis that is well known to us generally uses the green pigment, chlorophyll-a, to collect light (only energy from red light can be used) and use the energy to produce oxygen and glucose. Chlorophyll-a is found in all known plants, algae and cyanobacteria; for this reason, red-light harvesting was believed to be the basis of all photosynthesis. However, when exposed to near-IR radiation and no visible light, chlorophyll-f takes over and harvests lower-energy infrared rays to carry out photosynthesis. This is an extreme breakthrough as previously, it was thought that chlorophyll-f had no role asides from being an additional light-harvesting pigment. These insights are very important to science. This changes the entire textbook explanation of photosynthesis, as it shows that “accessory” chlorophylls such as chlorophyll-f are actually performing the crucial steps in converting light energy to chemical energy. Additionally, this study gives insight into life on other planets, as previously it was believed that plant-like life can only be found with the threshold being the “red limit”- the energy of red light which was thought to be the minimum energy for photosynthesis to occur- but now this breakthrough pushes the boundaries of how photosynthesis-like process can occur. Lastly, this process can be used in the real world to solve world hunger as it can help engineer food crops and plants that can perform more efficient photosynthesis using a wider range on the electromagnetic spectrum. It is simply amazing how much we have left to discover about natural processes on the earth, because we have only scratched the surface of what we can learn from them.