Chlorella is a genus of single- cell green algae belonging to the Chlorophyta division. It is spherical in shape, about 2 to 10 μm in diameter, and is without flagella . Chlorella contains the photosynthetic green pigment chlorophyll-a and -b in its chloroplast . Through photosynthesis , it rapidly multiplies, requiring only carbon dioxide , water , sunlight , and a small amount ofminerals to reproduce. 
The name Chlorella is taken from the Greek χλώρος, chloros , meaning green, and the Latin diminutive suffix ella , meaning small. German Biochemist and Cell Physiologist Otto Heinrich Warburg , awarded with the Nobel Prize in Physiology or Medicine in 1931 for his research on respiration , also studied photosynthesis in Chlorella . In 1961, Melvin Calvin of the University of California received the Nobel Prize in Chemistry for his research on the pathways ofcarbon dioxide assimilation in plants using Chlorella .
Many people believe Chlorella can serve as a potential source of food and energy because its photosynthetic efficiency can, in theory, reach 8%,  which exceeds that of other highly efficient crops such as sugar cane .
As a food source
Chlorella is a potential food source because it is high in protein and other essential nutrients; when dried, it is about 45% protein , 20% fat , 20% carbohydrate , 5% fiber, and 10% minerals and vitamins . Mass-production methods are now being used to cultivate it in large artificial circular ponds. It is also abundant in calories and vitamins. 
When first harvested, Chlorella suggests an inexpensive protein supplement to the human diet. Advocates Sometimes we focus Supposed other health benefits of the algae, Such As claims of weight control , cancer prevention , and immune system support .  According to the American Cancer Society , “available scientific studies do not support its effectiveness in preventing or treating cancer or any other disease in humans”. 
Under certain growing conditions, Chlorella yields are high in polyunsaturated fats – Chlorella minutissima has yielded EPA at 39.9% of total lipids. 
Following global fears of an uncontrollable human population boom during the late 1940s and the early 1950s, Chlorella was seen as a new and promising source of food and a possible solution to the then-current world hunger crisis. Many people during this time thought it would be an overwhelming problem and saw Chlorella as a way to end this crisis by providing large amounts of high-quality food for a relatively low cost. 
Many institutions, including the Carnegie Institution , the Rockefeller Foundation , the NIH , UC Berkeley , the Atomic Energy Commission , and Stanford University . Following World War II , many Europeans have been starving, and many Malthusians have caused this war, but also to the inability of the world to produce enough food to support the population increase. According to a 1946 FAO , the world would need to produce 25 to 35% more food in 1960 than in 1939 to keep up with the increase population, while health improvements would require a 90 to 100% increase. Because meat was costly and energy-intensive to produce, protein shortages were also an issue. Increasing cultivated area would provide adequate nutrition to the population. The USDA calculated that, to the US population by 1975, it would have to add 200 million acres (800,000 km²) of land, but only 45 million were available. One way to fight national food shortages has been developed for farmers, yet the American frontier and farm land had long since been extinguished in trade for expansion and urban life. Hopes rested solely on new agricultural techniques and technologies. Because of these circumstances, an alternative solution was needed.
To cope with the upcoming post-war population boom in the United States and elsewhere, Initial testing by the Stanford Research Institute showed that Chlorella (when growing in warm, sunny, shallow conditions) could convert 20% of solar energy into a plant that, when dried, contains 50% protein.  In addition, Chlorella contains fat and vitamins. The plant’s photosynthetic efficiency allows it to be more productive than any plant-one scientist predicted 10,000 tons of protein can be produced with just 20 workers staffing a one-thousand-acre (4-square kilometer) Chlorella farm. The pilot research performed at Stanford and elsewhere to huge numbers of newspapers and newspapers, and yet not to large scale algae production. Chlorella seemed like a viable option because of the technological advances in agriculture and the spread of it. Algae researchers had even hoped to add a neutralized Chlorella powder to the traditional products, as a way to fortify them with vitamins and minerals. 
When the preliminary laboratory results were published, the scientific community at first backed the possibilities of Chlorella . Science News Letter praised the optimistic results in an article entitled “Algae to Feed the Starving”. John Burlew, the editor of the Carnegie Institution of Washington’s Algal Book Culture-from Laboratory to Pilot Plant , stated, “the algae culture can fill a very real need,”  which Science News Letter turned into “future populations of the world will be kept alive by the production of or educated algae related to the green scum on ponds. ” The cover of the magazine featured Arthur D. LittleCambridge laboratory, which was a future food factory. A few years later, the magazine published an article entitled “Tomorrow’s Dinner”, which stated, “There is no doubt in the mind of scientists that the factories of the future will actually be factories.” Science Digest also reported, “common pond scum would soon become the world’s most important agricultural crop.” However, in the past, those claims have been made, have not been cultivated on that large scale.
Since the growing world food problem of the 1940s was made by farmers, Chlorella has not seen the kind of public and scientific interest that it had in the 1940s. Chlorella has a dietary supplement. 
The experimental research Was the carried out in laboratories, Rather than in the field, and scientists Discovered That Chlorella Would Be much more difficulty to Produce than Previously Thought. To be practical, the algae grown would have been placed in maximum light or in its maximum photosynthetic efficiency. Also, for the Chlorella to be as productive as the world would require, it would have been grown in carbonated water , which would have added millions to the production cost. A sophisticated process, and additional cost, was required to harvest the crop, and, for Chlorellato be a viable food source, its cell walls would have to be pulverized. The plant could reach its nutritional potential only in highly modified artificial situations. Another problem was developing palatable food products from Chlorella. 
Although the production of Chlorella has been promoted and made more creative, it has not been developed. It has not been sold on the scale of Spirulina , soybean products, or whole grains. Costs have remained high, and Chlorella has for the most part as a health food, for cosmetics, or as animal feed .  After a decade of experimentation, studies Showed That, Following exposure to sunlight, Chlorella captured just 2.5% of the solar energy, not much better than conventional crops.  Chlorella, too, was found by scientists in the 1960s to be impossible for humans and other animals to digest in its natural state to the tough cell walls encapsulating the nutrients, which presented further problems for its use in American food production. 
Use in carbon dioxide reduction and oxygen production
In 1965, the Russian CELSS experiment BIOS-3 determined that 8 m 2 of exposed Chlorella could remove carbon dioxide and replace oxygen in the environment for a single human. The algae were grown in vats underneath artificial light. 
Chlorella is consumed as a health supplement in the United States and Canada.  Chlorella has a number of purported health effects,  including an ability to treat cancer.  However, according to the American Cancer Society , “available scientific studies do not support its effectiveness for preventing or treating cancer or any other disease in humans”. 
A 2002 study showed that Chlorella cell walls contain lipopolysaccharides , endotoxins found in Gram-negative bacteria that affect the immune system and may cause inflammation .    However, more recent studies have found that lipopolysaccharides in organisms other than Gram-negative bacteria, for example in cyanobacteria, are significantly different from lipopolysaccharides in Gram-negative bacteria. 
Chlorella can create green and opaque water problems in aquaria . Chlorella can grow due to high nitrate and phosphate levels by direct sunlight. Decreasing phosphate and nitrate by water and moving the aquarium to shade can help alleviate the problem.
- Calvin cycle
- List of ineffective cancer treatments
- Quorn (food product)
- Soyuz 28 , 1978 Space mission which included experiments on Chlorella
- Spirulina (dietary supplement)
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