What are Algae?

Over the past 2 and a half millennia, algae have been utilized by humans for a variety of uses including industrial products, food, and pharmaceuticals. They are economically important, being used in foodstuffs, industrial chemicals, and pharmaceuticals.

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Algae – an Overview

Algae are photosynthetic eukaryotic organisms, belonging to the Protista kingdom. They are predominantly aquatic, although they are also found in other environments. They can be single cells or can exist in colonies of different cells. The size of species varies from microscopic ones such as Chlorella and diatoms to giant kelps with millions of cells.

The term algae is an informal one. Algae are a polyphyletic group, having no common ancestor. Their plastids seem to have an origin in cyanobacteria, though they were likely acquired in different manners.

In large, colonial algae, specialist cells perform distinct functions such as reproduction, photosynthesis, transport, and anchoring the colony to rocks and other media, making them complex and evolutionarily advanced organisms akin to multicellular lifeforms.

Algae: a Diverse Group of Organisms

Algae are an incredibly diverse group of organisms. Whilst one main definition is that they contain chlorophyll as their main photosynthetic pigment, Prototheca are a colorless species of algae that do not contain it. The range of photosynthetic pigments utilized by algae to create fuel for cells is much more varied than those used by plants.

Algae are classified into red, green, and brown algae based on their color. This is due to different pigments in their chloroplasts including chlorophylls, phycobiliproteins, and carotenoids. Besides these three main pigment groups, many others are recognized by phycologists.

Algae lack the features of true plants, such as true roots, leaves, and stems. They share this with the lower plants such as liverworts and mosses. They also lack specialized structures such as those required for reproduction, setting them apart from multicellular forms.

Additionally, some algae share several features with fungi and protozoa. Indeed, they can be difficult to distinguish from these organisms, although chloroplasts and their use of photosynthesis as a fuel source delineates them from these organisms. These species share more in common with fungi and protozoa evolutionarily than each other.

Different Types of Algae

There are several types of algae. How they are classified is based upon the morphology of their vegetative state.

In filamentous forms, the cells are arranged in string-like structures. Some filaments are unbranched, whereas others are branches. Examples of algae with unbranched filamentous forms include Spirogyra, whereas Stigeoclonium are branched, with a bush like appearance.

Many red algae such as Palmaria have numerous adjacent filaments which are joined laterally. Species such as kelp are parenchymatous (tissue-like.) Seaweeds such as Codium are coenocytic and grow to an enormous size without forming distinct cells. Coenocytic types are multinucleated, without cell walls to separate the organism’s protoplasm. Essentially, they are unicellular.

Still more algae are motile species which utilize flagella to move. Examples of this type include single-celled Ochromonas to huge colonial organisms such as Volvox, containing many thousands of cells.

Coccoid species have a set number of cells, whereas capsoid organisms have variable numbers of cells. Coccoid organisms (such as Scenedesmus) grow in size but not cell number once an exact figure is reached. Capsoid organisms (such as Chryscocapsa) have clusters of cells which are contained in a gel.

However, as many species can change their morphology over their life cycle or due to environmental reasons such as nutrient availability, classifying them based on this alone can be insufficient. For this reason, many scientists classify them based on differences and similarities in DNA and RNA. There is much debate as to how to accurately distinguish and classify each group.

Distribution and Abundance of Algae

Algae can be further classified according to the environment they inhabit. They are found in a staggering array of habitats, making them almost ubiquitous globally.

Planktonic algae grow in water and are microscopic. Neustonic algae are found on the surface of water (such as in the ocean, lakes, and rivers) and can be either microscopic or macroscopic. Cryophilic algae are found in ice and snow. Thermophilic algae grow in hot springs. Edaphic algae exist in soil. Those that grow in rock fissure are termed chasmolithic algae. Epilithic algae grow on rocks.

There are also classes of algae that specifically grow on other organisms. Epizoic algae grow on animals. Epiphytic algae grow on fungi, plants, or even other algae. Some species also grow inside other organisms, and these are known as endosymbionts.

An algae’s environment affects their diversity and abundance. Precipitation affects terrestrial algae, whereas light and nutrients affect aquatic species. Algal blooms are an example of this. Pollution leads to an increase in nutrients, causing overgrowth of aquatic algae. This causes oxygen depletion in the water, to the detriment of other species present.

Uses of Algae

Algae have been used by humans as a foodstuff for over 2500 years. Spirulina has been an important part of African and Central American diets for centuries. Seaweed has been traditionally used by European cultures as fertilizer and feedstock. They are an important dietary source of many compounds including fiber, proteins, polysaccharides, and lipids.

Today, algal species are used for many purposes in several sectors. These include the pharmaceutical, food, oil, agriculture, and industrial chemicals industries. Of the near 70,000 species identified, only 50 are in widespread commercial use. Examples of common applications include drinks, toothpaste, nutritional supplements, crude oil production, biofuels, drugs, and cosmetics.

In the pharmaceutical industry specifically, the secondary metabolites that are produced by marine algae are an attractive target for drug discovery. Algae are a commercially important source of these highly bioactive molecules. Chemicals extracted from algae show antiviral, anticancer, and antioxidant potential. Many studies are ongoing into the use of algae in several industries.

In Conclusion

Algae are an intriguing group of organisms that are hugely diverse and found in nearly every environment on earth. The evolutionary history of these organisms is complex and interesting, and new classifications are being discovered all the time. They are economically important organisms, and new uses are being found for them by scientists working in nearly every industry.


Further Reading

Last Updated: Oct 4, 2021

Reginald Davey

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Reginald Davey

Reg Davey is a freelance copywriter and editor based in Nottingham in the United Kingdom. Writing for News Medical represents the coming together of various interests and fields he has been interested and involved in over the years, including Microbiology, Biomedical Sciences, and Environmental Science.


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