Algae: Definition and Types

 

Definition

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 colors. For instance, algae living in snow contain carotenoid pigments in addition to chlorophyll, hence giving the surrounding snow a distinctive red hue.

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.

Algal cells are eukaryotic. For instance, algae can photosynthesize like plants, and they possess specialized structures and cell-organelles, like centrioles and flagella, found only in animals. The algal cell walls consist of mannans, cellulose and Galatians. 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
• Algae 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 coloration of the algae. Other pigments that provide green coloration (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.

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 indicators of environmental health, signaling the extent of pollution.

Examples of Algae

Prominent examples of algae include:

• Ulothrix
• Fucus
• Porphyra
• Spirogyra