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Algae : Definition, Classification and Types

The word "algae" refers to a wide collection of organisms that use photosynthesis to produce oxygen (the process of harvesting light energy from the sun to generate carbohydrates).

Algae are eukaryotic (nucleus-bearing) creatures that photosynthesize but lack the specialized multicellular reproductive systems of plants, which generally comprise fertile gamete-producing cells surrounded by sterile cells. Algae are also devoid of actual roots, stalks, and leaves, which they share with avascular lower plants (e.g., mosses, liverworts, and hornworts).

Algae can be as little as micromonas species or as large as 60 meters (200 feet) long kelps. Their photosynthetic pigments are more diverse than plants, and their cells possess characteristics that neither plants nor animals possess. In addition to their ecological roles as oxygen producers and the nutritional foundation for virtually all aquatic life, algae are commercially important as a source of crude oil, food, and a range of medical and industrial commodities for humans.


Algae are chlorophyll-containing, morphologically simple animals that range in size from tiny unicellular (single-celled) to very large multicellular organisms. There are no actual roots or leaves, and the algal body is generally homogeneous. Algae are primarily autotrophic, meaning they get their "food," or energy, from the sunlight in their environment. They play a crucial part in food chains and the preservation of our planet's oxygen supply.

Algae are referred to be "plants" at times and "protists" at other times (a grab-bag category of in general vaguely associated entities that are congregated on the basis of not existing as animals, plants, fungi, bacteria, or archaeans). Some algae (red algae and most green algae) are most closely connected to terrestrial plants, according to current phylogenetic analyses of evolutionary links, although other algae are related to specific protist groupings. As a result, algae are a genetically varied and extremely variable collection of creatures that belong to many different evolutionary lineages.


The word algae come from the Latin term "alga" which means "seaweed". Algal is a descriptive term that refers to, describes, or describes algae (e).


Algal taxonomy is a hotly debated topic that changes frequently as fresh molecular evidence becomes available. Phycologists study algae and phycology is the study of algae. Algae were first divided into broad groupings centered on color, for instance, red, brown, and green, in the 1830s. The colors reflect various chloroplast tinctures such as chlorophyll, carotenoids, and phycobiliproteins. There are many more pigment groups than three, and each class of algae has its own set of pigment types that are unique from the others. These beings aren't necessarily associated with one another. Though, many properties hitch them while differentiating them from the chief cluster of photosynthetic animals, terrestrial plants.


Algae and protozoa are classified as Kingdom Protista in the five-kingdom categorization system. They differ from protozoa in that they are photosynthetic. 'Euglenophyta' (euglenids), 'Chrysophyta' (diatoms), 'Pyrrophyta' (dinoflagellates), 'Chlorophyta' (green algae), 'Phaeophyta' (brown algae), and 'Rhodophyta' (red algae) are among the algae classified by the suffix -phyta. The traditional classification includes the 'Cyanophyta', or blue-green algae, which are prokaryotic organisms, however, they are now classed with bacteria under Kingdom Monera in modern taxonomy.


The fact that algae are aquatic and photoautotrophic eukaryotes is their most distinguishing trait. In comparison to other phototrophic eukaryotes, all organisms are photosynthetic and have very basic anatomy. Their body designs, on the other hand, might be single-celled or multi-cellular. The majority of algae species are single-celled. They are non-motile in certain cases and motile in others (flagellated). Some of them live in colonies or filaments, while others live alone. Multicellular organisms have a complicated structure that is divided into components that serve different roles. However, unlike bryophytes and tracheophytes, the body components are organ-like and not specialized into real leaves, stems, and roots. Algae, on the other hand, have pectin in their cell walls, which makes them slimy.


Although the majority of algae are phototrophic (meaning they get their energy from photosynthesis), some are mixotrophic, and still, others are heterotrophic. Photosynthesis and organic carbon absorption provide energy to mixotrophic algae (e.g. by osmotrophy, phagotrophy, and mixotrophy). Others lack pigments and thus turn colorless and are heterotrophic as a result.


It's also possible that the manner of reproduction differs. Several reproduce in an asexual manner, whereas others reproduce sexually. For example, Red algae and green algae have both throughout their life cycle. When the organism is diploid, it is in the asexual phase, and when it is haploid, it is in the sexual phase. A diploid zygote is molded when twofold haploid organisms combine.


Algae are plentiful and diversified in their distribution. They like damp and watery environments to dwell in. As a result, they may survive in freshwater, sea water, and wet terrestrial environments. Their abundance is strongly influenced by nutrients and light. As a result, there are times when nutrients are abundant, and their quantity can become great enough to trigger algal blooms or red tides.

Where Algae Live

Algae may be found almost anywhere where there is light for photosynthesis and water for reproduction. Algae are essential colonizers in broiling springs and lava pours, and these so-called extremophiles may thrive in extremely hot environments. An alga-like creature is among the most likely to be discovered if life exists beyond our solar system.

Types of Algae

Algae are divided into primary groupings based on their photosynthetic colors, which include green algae, red algae, brown algae, and golden algae. Others do not regard blue-green algae (Cyanophyta) to be algae, but rather group them alongside bacteria in the Kingdom Monera.

Algae : Definition, Classification and Types

i) Green algae

Any photosynthetic algae that contain the pigments Chlorophyll A and Chlorophyll B is referred to as green algae. Food is stored in plastids as starch. They come in a variety of forms, including unicellular (e.g. Micrasterias sp.), multicellular (e.g. Micrasterias sp.), and colonial (e.g. Micrasterias sp.). Those that seem filamentous or generate leaf-like thallus are multicellular types, e.g., Ulva and Volvox that form colonies. Charophytes (usually found in freshwater settings) and Chlorophytes are two types of green algae. Mostly marine, Green algae may also be found in terrestrial environments, e.g. soil, rocks and trees. On land, several green algae species have been discovered to develop symbiosis. For example, Chlorella species develops a symbiotic relationship with Hydra sp.

ii) Red algae

Rhodophyta is the phylum that includes red algae. Apart from chlorophyll, they are recognized by their red tint, which is attributed to the incidence of accomplice pigments in phycobillisomes such as Phycoerythrin, Phycocyanin, and Allophycocyanins. Examples of red algae include Rhodella, Compsopogon, Stylonema, Bangia, Porphyra, Porphyridium cruentum, Hildenbrandia, Nemalion, Corallina officinalis, Ahnfeltia, Gelidium, and others.

iii) Euglenophyta

Euglena is a protist that lives in both fresh and saltwater. Plant cells, like some euglenoids, are autotrophic. They have chloroplasts and are capable of photosynthesis. They have a protein-rich covering called the 'pellicle' that shields them instead of a cell wall. Other euglenoids, like animal cells, are heterotrophic, meaning they feed on carbon-rich substances found in the water and unicellular creatures. With the right organic material, certain euglenoids can survive in the dark for a while. The eyespot, flagella, and organelles are all features of photosynthetic euglenoids (nucleus, chloroplasts, and vacuole).

IV) Chrysophyta (Golden-brown algae and Diatoms)

The most common forms of unicellular algae are golden-brown algae and diatoms, which account for over 100,000 distinct species. Both may be found in both fresh and salt water. Diatoms are a form of plankton found in the water that is far more prevalent than golden-brown algae. Diatoms have a 'frustule', which is a silica shell that varies in shape and structure according to the species. The productivity of golden-brown algae in the ocean is comparable to that of diatoms, despite their smaller numbers. Because their cells are under 50 micrometers in diameter, they're called nanoplankton.

V) Pyrrophyta (Fire Algae)

Fire algae are unicellular algae that employ flagella for movement and are often found in seas and certain fresh water sources. Dinoflagellates and cryptomonads are the two classes of pyrrophyta. Dinoflagellates can generate a red tide, which causes the water to become red owing to their abundance. Other Pyrrophyta species, like some fungi, are bioluminescent. They give the impression that the water is on fire at night. Dinoflagellates are also dangerous because they create a neurotoxin that may cause muscle damage in humans and other animals. Cryptomonads, like dinoflagellates, may cause harmful algal blooms that color the water 'red' or 'dark brown'.

VI) Paeophyta (Brown Algae)

Brown algae are the biggest algal species, consisting of seaweed and kelp variants found in marine habitats. These creatures have an 'anchoring organ', 'air pockets' for buoyancy, a stalk, 'photosynthetic organs', and 'reproductive tissues' that produce spores and gametes. These protists have an alternation of generations throughout their life cycle. Sargassum weed, rockweed, and gigantic kelp, which may grow to be 100 meters long, are examples of brown algae.

VII) Xanthophyta (Yellow-Green Algae)

The number of species of yellow-green algae is the smallest, ranging from 450 to 650. They are single-celled creatures having cellulose and silica cell walls and one or two flagella for movement. Their chloroplasts are devoid of a pigment, making them seem lighter in hue. They grow in tiny colonies with only a few cells. Yellow-green algae are most commonly seen in freshwater, although they may also be found in saline water and damp soil.

Algal Biofuel

Algae may now be utilized as a source of fuel thanks to recent advances in science and technology. The introduction of eco-friendly alternatives such as algae biofuel has been pushed by global demand for petroleum goods and worsening environmental health. As a result, algal fuel is becoming a more realistic alternative to conventional fossil fuels. Everything from "green" diesel to "green" jet fuel is made with it. It's similar to other corn and sugarcane-based biofuels.

Next TopicBlue-green Algae

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