Can you imagine Earth without plants? The thought of a plantless planet is scary as well as worrisome. Plants are the ultimate source of energy for every single living being on Earth, one way or another. They carry out a physio-chemical process called Photosystnesis for converting solar energy into chemical energy. Basically, this energy conversion provides energy for producers and consumers. Photosynthesis powers 99% of Earth’s ecosystem and is a vital life-supporting process.
Looking for Photosynthesis examples in real life? First, let’s quickly understand the concept of photosynthesis.
Solar energy is a high-energy source that is captured by photoautotrophs in the form of light energy. Photoautotrophs are organisms that are capable of making their own food in the presence of sunlight and hence are called producers. Producers use light energy and raw materials to produce food in the form of Carbohydrates. These raw materials are simple organic compounds such as CO2 gas, and water. Photoautotrophs (producers) convert these simple organic molecules into Carbohydrates and Oxygen. Carbohydrates can be stored as starch, and used in cellulose production and respiration. Oxygen is released into the atmosphere. Carbohydrates are used as a food source by both the producers and the higher organisms in the food chain. These higher organisms comprise heterotrophs which rely on photoautotrophs for food. Hence, photosynthesis is a vital source of energy for most of the life forms on Earth. (Most, not all forms because there are certain organisms such as chemoautotrophs that do not rely on photosynthesis for food synthesis).
Note: Photosynthesis requires photosynthetic pigments such as Chlorophyll, Carotenoids, and Phycobilins that collectively facilitate photosynthesis.
Green plants carry out photosynthesis in specialized organelles called chloroplasts, which contain a photosynthetic pigment called chlorophyll. Chlorophyll captures light energy and converts it into chemical energy (Carbon compounds that are converted into carbohydrates). Non-green plants also photosynthesize, though they have very low levels of chlorophyll. Chlorophyll is an essential factor for photosynthesis in plants. Non-green plants have pigments such as anthocyanins and carotenoids that make up for the lower levels of chlorophyll. Not all plants perform photosynthesis. Cuscuta (amarbel) is one such example of a non-photosynthetic plant with a parasitic mode of nutrition.
Algae are photosynthetic eukaryotes that are found in aquatic environments, moist soil, and rocks. They show characteristics of both plants and animals with the presence of plant-like photosynthetic organelles and animal-like ability to feed on organic matter. Due to their photosynthetic properties, algae have important ecological roles to maintain the cycle of oxygen and carbon. They are oxygen producers, generating half of the global oxygen supply, and are major food sources for various aquatic organisms. Types of photosynthetic algae include phytoplanktons. Freshwater phytoplanktons comprise green algae and cyanobacteria, and marine phytoplanktons comprise diatoms and dinoflagellates.
Euglena are unicellular protists that inhabit moist soil, freshwater, marine water, marshes, the surface of lakes, and ponds with exposure to sunlight. Euglena sets an excellent example of mixotrophic nutrition; it produces food through photosynthesis in the presence of light and adopts the heterotrophic mode of nutrition in the absence of light. They possess photosynthetic ability due to the presence of plastids (like plants), and can also locomote in search of food (like animals). Like Algae, Euglena also shows characteristics of both plants and animals, and belongs to a separate kingdom (Protista).
Photoautotrophic bacteria that photosynthesize, with oxygen given out as a byproduct, are called oxygenic photosynthetic bacteria. The main photosynthetic pigments are chlorophyll a and b. The best-known example of oxygenic photosynthetic bacteria are cyanobacteria.
Cyanobacteria are one of the ancient photosynthetic microbial species on Earth responsible for supplying oxygen to the primordial atmosphere (which only had nitrogen, CO2, and water vapour). They carry out photosynthesis like plants and algae but are prokaryotic organisms. They are found in land, damp soil, bare rock, aquatic ecosystems, and extreme environments like hot springs and hypersaline lakes (hence are considered extremophiles). They contain photosynthetic pigments, phycocyanin (blue) and phycoerythrin (red) due to which they were formerly known as blue-green algae (however, they are not algae). Cyanobacteria are also nitrogen fixers and live in symbiotic relationships with nitrogen-fixing organisms. Examples of Cyanobacteria species are Prochlorococcus, Nostoc, Synechococcus, Oscillatoria, Spirulina, Microcystis, Anabaena, Gloeocapsa, etc.
5. Proteobacteria (purple bacteria)
Purple sulfur bacteria are commonly found in stratified aquatic environments lacking oxygen such as hot springs, sulfur springs, meromictic lakes (layers of water do not intermix), and intertidal microbial mats. Examples of proteobacteria include species of Rhodobacter, Chromatium, Rhodopseudomonas, and Halorhodospira. This is an example of Anoxygenic photosynthetic bacteria.
Heliobacteria are the only known photoheterorophic bacteria with a gram-positive cell wall, have no capacity for autotrophic growth, and uniquely possess a photosynthetic pigment bacteriochlorophyll (BChl) g. They are found in the soil of paddy fields, other types of soils, and rarely in aquatic environments. The most commonly known heliobacteria are Heliobacterium mobilis and Heliobacterium modesticaldum. This is an example of Anoxygenic photosynthetic bacteria.
7. Chlorobi (Green sulfur bacteria)
Chlorobi bacteria use reduced sulfur compounds for photosynthesis with the help of pigments Bacteriochlorophylls c, d, and e as per the variable species. They are found in anaerobic, sulfur-rich aquatic environments, and the uppermost layer of oceans (where they stay protected from atmospheric oxygen while using light energy for photosynthesis). Some examples of Chlorobi species include Chlorobium tepidum, Chlorobium phaeobacteroides, and Chlorobium phaeovibrioides. This is an example of Anoxygenic photosynthetic bacteria.
8. Chloroflexi or Chlorobacteria (Green non-sulfur bacteria)
Chloflexi or the green non-sulfur bacteria derive their name due to the presence of green flexible filaments called the green flexibacteria. This species of Chloroflexota phylum are anoxygenic photoautotrophs, that thrive in diverse habitats including sediments and hot springs. They carry out photosynthesis in chlorosomes with pigments bacteriochlorophyll a, c, and d. This is an example of Anoxygenic photosynthetic bacteria.
Another proof of photosynthesis in real life is humans. Let’s put it this way, you feel hungry, you eat, and you feel good. You go longer without eating anything and your body literally starts breaking down. Why is that? It’s because the food you consume provides you with the energy that was trapped by a plant-based source. The same logic applies to non-vegetarians as well. Animal products come from an animal (or bird) that obtains its energy from plants.