Algae are a diverse group of protists that have simple, thalloid bodies that lack true stems, roots, and leaves. Algae do not share a common ancestor and hence, are not related to each other (polyphyletic). The absence of vascular tissues i.e. as xylem and phloem, is one of the characteristics of algae. They come in both single- and multicellular forms. Prokaryotic or single-celled algae are a subclass of the phylum Cyanophyta, which also includes cyanobacteria and blue-green algae.
However, because prokaryotic algae lack specific membrane structures and a clearly defined nucleus, they are not regarded as true algae and are instead placed in the domain of bacteria. Oppositely, multicellular or eukaryotic algae belong to the kingdom (Protista) and domain (Eukarya). They have membrane-bound organelles, a clearly defined nucleus, and chloroplasts. Additionally, certain eukaryotic algae include pyrenoids in their plastids. Giant kelp and brown algae are two examples of multicellular algae. Examples of unicellular organisms include dinoflagellates, euglenophytes, and diatoms.
Types of Algae
Algae are mostly divided into the following classes according to characteristics like habitat and pigmentation:
- Chlorophyta (Green algae): They typically live in freshwater and contain chlorophyll pigment. Sea lettuce, horsehair algae, etc., are examples of green algae.
- Rhodophyta (Red algae): They prevalently inhabit tropical marine environments and contain phycoerythrin pigment. Gracilaria, Euchema, Porphyra, etc., are examples of red algae.
- Phaeophyta (Brown algae): They are prominently found in marine environments and contain fucoxanthin pigment. Seaweed and kelp constitute the largest group of brown algae.
- Xanthophyta (Yellow-green algae): They are the least common species of algae, which mainly inhabit freshwater and marine water. Heterochloris, Misclococcus, Chlorogloea, etc., are examples of yellow-green algae.
- Pyrrophyta (Fire algae): They commonly occur near the oceans and in freshwater. Dinoflagellates and Cryptomonads are examples of fire algae.
- Chrysophyta: It includes golden-brown algae and diatoms. Both the members of diatoms and golden-brown algae are common in fresh and saltwater environments.
- Euglenophyta: It includes Euglenoids that inhabit as fresh and saltwater protists.
Characteristics of Algae
Algae have certain general features that are shared by both plants and animals. for example, it photosynthesize like plants and also have specialized cell organelles like centrioles and flagella that are exclusively found in animals. Mannans, cellulose, and Galatians make up the algal cell walls.
Some of the general characteristics of algae are listed below;
- 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.
Habitat
Algae primarily grow in aquatic environments, such as freshwater and saltwater, while some may also thrive in terrestrial habitats. A variety of substrates, including tree trunks, stones, snowbanks, and others, are home to certain algae. Some may coexist well with creatures like mushrooms, sponges, ciliates, and mollusks. For instance, lichens exhibit a symbiotic relationship with ascomycete fungi and cyanobacteria (blue-green algae).
Algae Mode of Nutrition
Although, the principal mode of nutrition in algae is through “Photoautotrophy” or “Self-feeding”. The others may show some different feeding mechanisms, based on which algae are classified into the following types:
- Obligate phototrophs: Algae belonging to this group primarily obtain nutrition via utilizing inorganic sources like CO2, H2O and sunlight or through photosynthesis. In case of limited sunlight, obligate phototrophic algae sustain life through phagotrophy or osmotrophy. Examples: Dinobryon divergons, Heterokontophyta, etc.
- Obligate heterotrophs: Algae belonging to this group primarily obtain nutrition by a heterotrophic mode. In conditions of limited heterotrophy, they sustain themselves by undergoing phototrophy. Examples: Dinophyta, Gymnodium gracilentum, etc.
- Facultative mixotrophs: Algae belonging to this group obtain nutrition through photoautotrophy as well as heterotrophy. Example: Dinophyta.
- Obligate mixotrophs: Algae belonging to this group primarily obtain nutrition through photoautotrophy and need B-complex vitamins, amino acids, and fatty acids for growth. Examples: Euglena gracilis, Euglenophyta, etc.
Algae Biofuel
Algal fuel can now be produced thanks to recent advances in science and technology. The employment of environmentally acceptable alternatives like algae biofuel has been encouraged by worsening environmental health and a global need for petroleum-based products. As a result, algal fuel is becoming a more and more viable substitute for conventional fossil fuels. Everything from “green” jet fuel to “green” diesel is produced with it. It is comparable to other corn- and sugarcane-based biofuels.