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The Mystery of Microalgae: Why Do These Tiny Organisms Produce Half of the Earth's Oxygen?
On Earth, there is a kind of tiny organisms that silently provide important support for our survival. They are microalgae. These microscopic organisms, which are invisible to the naked eye, are primarily phytoplankton and live in a variety of freshwater and marine systems. Possessing the characteristics of a single cell, microalgae can live alone, or in chains or colonies. Depending on the species, microalgae range in size from a few micrometers to several hundred micrometers. Unlike higher plants, microalgae have no roots, stems or leaves, which allows them to adapt to environments dominated by viscous forces.
Microalgae are photosynthetic organisms essential to life on Earth; they produce about half of all oxygen and use the greenhouse gas carbon dioxide to grow photoautotrophically.
Microalgae and cyanobacteria together make up phytoplankton, which dominates ocean photosynthesis. As the basis of the food chain, microalgae, together with bacteria, provide energy for all trophic levels in the biosphere. As ecosystems change, microalgae are able to adjust their chemical composition to adapt to environmental changes, giving them great flexibility in how they grow and reproduce.
Chemical composition and application of microalgae
The chemical composition of microalgae is not a fixed factor and is affected by many factors, including differences in species and culture conditions. Some microalgae have the ability to adapt to changes in their environment and adjust their chemical composition accordingly. Particularly in a phosphorus-deficient environment, they are able to replace phospholipid globules with phosphate-free lipids.
Microalgae can accumulate desired products by modifying environmental factors such as temperature, light, pH, carbon dioxide supply, salts and nutrients, which makes them a viable resource.
In addition, chemical signals secreted by microalgae have important influences on prey selection, defense and escape behaviors in the biosphere. These chemical signals play an important role in large-scale ecological structures, such as algal blooms. Microalgae are also an essential food source for many aquaculture species, especially filter-feeding bivalves.
Photosynthetic and chemosynthetic microalgae
Photosynthetic and chemosynthetic microorganisms can form a symbiotic relationship with the host organism and provide it with vitamins and polyunsaturated fatty acids required for growth. Because these cells grow in water, they can efficiently acquire water, carbon dioxide, and other nutrients. Additionally, while fish oil gets a lot of attention for its omega-3 fatty acids, fish do not actually produce these omega-3s, but rather accumulate their omega-3s by consuming microalgae.
Microalgae can accumulate considerable amounts of protein, depending on the species and cultivation conditions, and because they can be grown on non-agricultural land, this makes microalgae an alternative protein source for human or animal feed.
At the same time, microalgae proteins are also used in the food industry as thickeners or emulsifiers and foam stabilizers to replace animal-derived proteins. Some microalgae also accumulate pigments, such as chlorophyll, carotenoids and photocyanin, which can be extracted and used as colorants.
Cultivation of microalgae
Various microalgae species are produced in captive farms and used for a variety of commercial purposes, including human nutrition, as biofuel, in aquaculture of other organisms, in the production of pharmaceuticals and cosmetics, and as biofertilizer. However, low cell density is a major bottleneck in the commercialization of microalgae-derived products. Studies have shown that the success of microalgae cultivation systems is influenced by a variety of factors, including: the geometry and size of the cultivation system (called a photosynthetic reactor), light intensity, carbon dioxide concentration in the gas phase, nutrient levels (mainly nitrogen, phosphorus, potassium) and culture mixing method.
With the advancement of science and technology, our research on microalgae has become increasingly in-depth, and the potential value of these tiny organisms is gradually being developed. In the future, microalgae may play an important role in combating global climate change and increasing food supply. However, have we fully recognized and utilized the value of these microalgae?
