What Are Algae?

Photosynthesis is a process carried out by various aquatic organisms, including algae. Some algae are familiar to most people, such as seaweed (such as kelp or phytoplankton), pond scum, and algal blooms in lakes. But, there is a vast and varied world of algae that are not only helpful to us, but also crucial to our survival. 

Definition 

Various organisms produce oxygen through photosynthesis (the process of harvesting light energy from the sun to generate carbohydrates). Their relationship is not certain. They do however share certain characteristics with the other major group of photosynthetic organisms: the land plants. 

According to "Algae: Anatomy, Biochemistry, and Biotechnology, 2nd Ed." (CRC Press, 2014), algae are not highly differentiated. Their bodies lack true roots, stems, and leaves, as well as a vascular system to circulate water and nutrients. According to a 2014 article published in the journal Current Biology, many algae are unicellular. Different types and sizes of algae also exist. The simplest form is a single, microscopic cell; the largest form is a multicellular organism; colonies exist; and the simplest form is a leaf, as in seaweeds such as giant kelp. Picoplankton have a diameter of 0.2 to 2 micrometers, whereas giant kelp can grow up to 60 meters in length. Algae can be found in both freshwater and saltwater habitats.

Therefore, the term "algae" includes both prokaryotic organisms (cyanobacteria, also known as blue-green algae) and eukaryotic organisms (all other algal species). Linda Graham, a professor of botany at the University of Wisconsin-Madison, explains that cyanobacteria are often grouped with algae since they don't belong to a group that shares a common ancestor. Eukaryotic algae do not include cyanobacteria. Furthermore, it is interesting to note that land plants' chloroplasts, which are responsible for photosynthesis, are adapted forms of cyanobacteria. Early cyanobacteria were eaten by primitive plant cells sometime during the Proterozoic or Cambrian periods, according to the University of California Museum of Paleontology.

(Prokaryotes include bacteria and archaea. They are simpler organisms without an On the other hand, eukaryotes are living organisms such as protists, plants, fungi, and animals. Their cells are more organized. They have structures called organelles that perform a range of cellular functions, and their DNA is placed in a central compartment called the nucleus.)

General characteristics

Habitat

Most algae live in aquatic habitats (Current Biology, 2014). Even so, the word "aquatic" is almost useless in describing the diversity of these habitats. In saltwater oceans or freshwater lakes, these organisms can thrive. Temperatures, oxygen or carbon dioxide concentrations, acidity and turbidity are also no match. As an example, giant kelps are found at depths of more than 200 meters under polar ice sheets, while Dunaliella salina, a single-celled green alga, can be found in hypersaline environments such as the Dead Sea, according to a review article published in the journal Saline Systems in 2005. A planktonic algae is a free-floating, mostly unicellular algae that lives within illuminated regions of water. Benthic algae adhere to surfaces. According to "Algae," these algae grow on mud, stones, other algae, plants, or animals.

It is also possible for algae to live on land. Tree trunks, animal fur, snow banks, hot springs (as described in "Algae"), and soil, including desert crusts, are examples of unexpected places where they grow.

Generally, algae live separately in the forms in which they grow (single cells, colonies, etc.), but they can also form symbiotic relationships with ciliates, sponges, mollusks and fungi (as lichens). These relationships provide algae with the opportunity to expand their habitat horizons.

Nutrition

As a general rule, algae are able to photosynthesise and are able to produce carbohydrates and oxygen from sunlight and carbon dioxide. In other words, most algae are autotrophs or, more specifically, photoautotrophs (indicating that they generate nutrients with light energy).

A few algal species, however, are heterotrophic, which means they obtain all their nutrition from sources outside of themselves. Diverse heterotrophic strategies are employed by these species to acquire nutrients from organic materials (carbon-containing compounds such as carbohydrates, proteins, and fats). Phagotrophy is characterized by the engulfment of dissolved substances, while osmotrophy is the absorption of dissolved substances. Auxotrophic algae require only essential vitamins like B12 and fatty acids (according to Algae). 

According to the authors of "Algae," algae utilize a variety of dietary strategies including photoautotrophy and heterotrophy. This is called mixotrophy.

Reproduction

Algae are capable of reproducing through asexual or vegetative methods and via sexual reproduction. 

In algae, asexual reproduction involves the production of a motile spore, whereas vegetative reproduction involves simple cell division (mitosis) to create identical offspring and colonial fragmentation. Sexual reproduction involves the union of gametes (produced in each parent individually through meiosis).

Classification

Cyanobacteria

are also called blue-green algae. Despite their ability to conduct oxygen-producing photosynthesis and the fact that they live in many of the same environments as eukaryotic algae, cyanobacteria are prokaryotes and therefore gram-negative bacteria. The organisms are also capable of independently conducting nitrogen fixation, which is the process of converting atmospheric nitrogen into usable forms, such as ammonia. 

Blue is the prefix of the word "cyano". Bacteria have pigments that absorb specific wavelengths of light and give them their characteristic colors. The blue pigment phycocyanin, which absorbs red wavelengths of light, is present in many cyanobacteria. Chlorophyll is a green pigment that helps cyanobacteria harvest light during photosynthetic processes (Current Biology, 2014). Another pigment found in some bacteria is phycoerythrin, which absorbs light with a green region and gives it a pink or red color. 

Eucaryotic algae contain this pigment.

Eukaryotic algae are polyphyletic, meaning they did not evolve from one common ancestor. We see this in our understanding of the tree of life, a family tree of all living organisms organized by their evolutionary relationships. There are many different groups of eukaryotic algae, or major branches of the tree.

In a 2014 The review article by Fabien Burkilists five supergroups of eukaryotic organisms: Ophiskontha, Amoebozoa, Excavata, Archaeplastida and SAR (three groups of Stramenopiles)., Alveolata and Rhizaria). 

Among the Archaeplastida are both plants and photosynthetic algae such as chlorophytes (a subset of green algae), charophytes (mainly freshwater green algae) and glaucocystophytes (unicellular freshwater algae). Chlorophytes are green algae which form lichen partnerships with fungi. 

Alveolata contain Dinoflagellates. They are mostly unicellular marine or freshwater organisms. Dinoflagellates have evolved without their plastids - the site of photosynthesis - and are phagotropic or parasitic. A number of other algal species are found among Alveolata, Excavata, Rhizaria, and Chromista (Current Biology, 2014).

The primary contribution of algae to our environment and well-being is their ability to produce oxygen through photosynthesis. Approximately half of the oxygen in the Earth's atmosphere is produced by algae, Graham told LiveScience.

According to a review article published in 2010 in the journal Biofuels, petroleum is derived in part from ancient algae deposits. According to Graham, cyanobacteria may have produced some of the older oil deposits, though the identity of the producers is still unknown. The younger oil deposits probably resulted from eukaryotic marine algae, coccolithophorids, and other microscopic marine phytoplankton." These oil deposits are a limited resource and are slowly dwindling with human usage. Researchers are searching for renewable alternatives as a result.

Algal biofuels are one of the most promising alternatives to fossil fuels. All algae have the ability to produce energy-rich oils, and several microalgal species accumulate high levels of oil in their dry mass. In addition, algae can reproduce quickly and use carbon dioxide efficiently. "Algae help to keep atmospheric carbon dioxide levels stable by storing [the gas] in organic materials, such as oil deposits and inorganic carbonate rocks," Graham added. Green algae, diatoms, and cyanobacteria are among the microalgal species that could provide biofuels. (Biofuels, 2010). 

Algal blooms

Algae, or algal blooms, have a bad reputation for causing toxic conditions in oceans and lakes. "Algal blooms" refer to the rampant growth of certain microalgae, which, in turn, produces pollutants, disrupts aquatic ecosystems, and increases water treatment costs, according to the Environmental Protection Agency (EPA). Under natural conditions, Graham notes that algae use toxins to protect themselves from being eaten by small animals and only need a small amount to do so. Oceans contain toxins produced by dinoflagellates and diatoms, while freshwater is home to cyanobacteria, which also produce toxins..

The main cause of algal blooms is nutrient pollution, which occurs when there is an excess of nitrogen and phosphorus. The pollution occurs from a variety of human activities, including the use of fertilizers in agriculture and animal manures. Untreated wastewater is also high in nitrogen and phosphorus.  

Algae are often perceived as noxious by society and should be eliminated whenever possible. "But that perception is incorrect because algae make oxygen, fish [they provide food for aquatic organisms], oil, and many other useful materials," Graham told LiveScience. "Only a few species cause problems, and the worst of these is humanity."