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What are Algae?

Algae exist in environments ranging from oceans, rivers, and lakes to ponds, brackish waters, and even snow. Algae are usually green, but they can be found in a variety of different colours. For instance, algae living in snow contain carotenoid pigments in addition to chlorophyll, hence giving the surrounding snow a distinctive red hue

Algae Definition

“Alga is a term that describes a large and incredibly diverse group of eukaryotic, photosynthetic lifeforms. These organisms do not share a common ancestor and hence, are not related to each other (polyphyletic).”

Multicellular examples of algae include the giant kelp and brown algae. Unicellular examples include diatoms, Euglenophyta, and Dinoflagellates.

Most algae require a moist or watery environment; hence, they are ubiquitous near or inside water bodies. Anatomically, they are similar to another major group of photosynthetic organisms – the land plants. However, that is where the differences end as algae lack many structural components typically present in plants, such as true stems, shoots, and leaves. Furthermore, they also do not have vascular tissues to circulate essential nutrients and water throughout their body.

Characteristics of Algae

Specific general characteristics of algae are common to plants as well as animals.

For instance, algae can photosynthesize like plants, and they possess specialized structures and cell-organelles,like centrioles and flagella, found only in animals. Listed below are some of the general characteristics of algae.

  • Algae are photosynthetic organisms
  • Algae can be either unicellular or multicellular organisms
  • Algae lack a well-defined body, so, structures like roots, stems or leaves are absent
  • Algaes are found where there is adequate moisture.
  • Reproduction in algae occurs in both asexual and sexual forms. Asexual reproduction occurs by spore formation.
  • Algae are free-living, although some can form a symbiotic relationship with other organisms.

Types of Algae

There are many types of algae; however, these are some of the more prominent types:

Red Algae

Also called Rhodophyta, it is a distinctive species found in marine as well as freshwater ecosystems. The pigments phycocyanin and phycoerythrin are responsible for the characteristic red colouration of the algae. Other pigments that provide green colouration (such as chlorophyll a) are present. However, they lack chlorophyll b or beta-carotene.

Green Algae

It is a large, informal grouping of algae having the primary photosynthetic pigments chlorophyll a and b, along with auxiliary pigments such as xanthophylls and beta carotene.

Higher organisms use green algae to conduct photosynthesis for them. Other species of green algae have a symbiotic relationship with other organisms.

Members are unicellular, multicellular, colonial and flagellates. Prominent examples of green algae include Spirogyra, Ulothrix, Volvox, etc. 

Not an Algae: Blue-green Algae

In the past, blue-green algae were one of the most well-known types of algae. However, since blue-green algae are prokaryotes, they are not currently included under algae (because all algae are classified as eukaryotic organisms).

Also called cyanobacteria, these organisms live in moist or aquatic environments just like other algae. These include dams, rivers, reservoirs, creeks, lakes and oceans. This class of bacteria obtains energy through the process of photosynthesis. Ecologically, some species of blue-green algae are significant to the environment as it fixes the nitrogen in the soil. Hence, these are also called nitrogen-fixing bacteria. E.g. Nostoc, Anabaena, etc.

However, other types of blue-green algae can be toxic to human beings. They can either be neurotoxic (affects the respiratory or nervous system, causing paralysis) or hepatotoxic (causes the liver to fail). Moreover, some can act as the indicators of environmental health, signalling the extent of pollution.

Examples of Algae

Prominent examples of algae include:

  • Ulothrix
  • Fucus
  • Porphyra
  • Spirogyra

Algal Biofuel

Recent developments in science and technology have enabled algae to be used as a source of fuel. Global demand for petroleum products and declining environmental health has prompted the use of eco-friendly alternatives such as algal biofuel. Hence, algae fuel is an increasingly viable alternative to traditional fossil fuels. It is used to produce everything from “green” diesel to “green” jet fuel. It is similar to the other biofuels made from corn and sugar-cane.