Kingdom Plantae – Algae

Introduction

Whittaker (1969) offered a comprehensive taxonomy of living creatures based on the Five Kingdoms classification, including Monera, Protista, Fungi, Animalia and Plantae. Plantae is the plant kingdom that consists of Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.

Algae

The kingdom Plantae includes all forms of algae. Algae are chlorophyll-containing creatures: simple, thalloid, autotrophic and mostly aquatic (freshwater and sea). They may be found in various environments, including damp stones, soil and wood. Some of them are also combined with fungi (lichen) and mammals (for example, on sloth bears).

Algae vary significantly in size and shape, from colony forms like Volvox to filamentous structures like Ulothrix and Spirogyra. Some marine species, such as kelps, have massive plant bodies. Reproduction in algae is through vegetative duplication, asexual reproduction and sexual reproduction.

Blue-Green Algae

Blue-green algae were formerly among the famous forms of algae. However, as blue-green algae are prokaryotes, they are not officially categorised as algae (as all algae are eukaryotic organisms).

These creatures, also known as cyanobacteria, dwell in damp or watery settings, exactly like other algae. They are usually found in dams, rivers, reservoirs, streams, lakes and seas. Photosynthesis is the method through which this type of bacteria obtains energy. Some blue-green algae are essential to the ecosystem because they fix nitrogen in the soil. As a result, these bacteria are also known as nitrogen-fixing bacteria, with Nostoc and Anabaena being two such bacterial species.

The colonies are usually encased in a gelatinous sheath. They frequently create blooms in contaminated bodies of water. Some of these species, such as Nostoc and Anabaena, can fix atmospheric nitrogen in specialised cells known as heterocysts. They play an essential role in recycling nutrients like nitrogen, phosphorus, iron and sulphur. Chemosynthetic autotrophic bacteria oxidise inorganic compounds such as nitrates, nitrites and ammonia and utilise the energy generated to produce ATP.

Types of Algae

There are three classes of algae: Chlorophyceae, Phaeophyceae and Rhodophyceae.

Chlorophyceae

Chlorophyceae members are generally referred to as green algae. Plant bodies can be unicellular, colonial or filamentous. Owing to the prevalence of the pigments chlorophyll a and b, they are often grass green. The pigments are concentrated in certain chloroplasts. In various species, the chloroplasts might be discoid, plate-like, reticulate, cup-shaped, spiral-shaped or ribbon-shaped. The majority of the members have one or more pyrenoids, storage bodies in the chloroplasts. Some algae may be capable of storing food in the form of oil droplets.

Green algae often have a stiff cell wall composed of an inner layer of cellulose and an outer layer of pectose.

Vegetative reproduction is often accomplished by fragmentation or generating various types of spores. Flagellated zoospores developed in zoosporangia are used for asexual reproduction. Sexual reproduction differs significantly in the kind and creation of sex cells, and it can be isogamous, anisogamous or monogamous and oogamous. Widely seen green algae include Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara.

Brown Algae

Phaeophyceae, sometimes known as brown algae, are primarily found in marine environments. However, they vary significantly in size and shape. They range from primary branching, filamentous forms (Ectocarpus) to lavishly branched forms like kelps, which may grow 100 metres tall. They include chlorophylls a and c, as well as carotenoids and xanthophylls.

The quantity of the xanthophyll pigment, fucoxanthin, present in them determines their colour, ranging from olive green to different hues of brown. Food is stored in complex carbs such as laminarin or mannitol. The vegetative cells contain a cellulose wall generally coated by an algin thick covering on the exterior. In addition to plastids, the protoplast has a centrally positioned vacuole and nucleus. The plant body is generally held to the substratum by a holdfast and consists of a stalk, the stipe, and a leaf-like photosynthetic organ called the frond.

Red Algae

Rhodophyceae members are usually referred to as red algae due to the prevalence of the red pigment r-phycoerythrin in their bodies. Most red algae are marine, with high numbers seen in warm locations. The red thalli of the majority of red algae are multicellular. Some of them have complicated bodily structures. The food is retained as Floridean starch, identical to amylopectin and glycogen. Red algae have doubled cell walls. Most of the inner walls are made of cellulose and outer walls are made of carrageenan. They even have the most gene-rich plastid genomes found to date. Red algae lack flagella and centrioles during their whole life cycle. Pit connections and pit plugs are defining features of red algae that appear after mitosis during the cytokinesis process. Red algae have incomplete cytokinesis.

Red algae often proliferate vegetatively by fragmentation. They reproduce both asexually and sexually using non-motile spores and non-motile gametes. Sexual reproduction is oogamous, with extensive post-fertilization processes. Polysiphonia, Porphyra, Gracilaria and Gelidium are the most prevalent members.

Uses of Algae

Algae may help humans in several ways. Algae photosynthesis accounts for at least half of the carbon dioxide fixing on Earth. Owing to them being photosynthetic, they can increase the amount of dissolved oxygen in their immediate surroundings. They are crucial as the primary producers of energy-rich chemicals that serve as the foundation of all aquatic creatures’ feeding cycles. Among the 70 species of sea algae utilised as food, there are several Porphyra, Laminaria and Sargassum species. Certain coastal brown and red algae, such as algin (brown algae) and carrageenan (red algae), generate vast amounts of hydrocolloids (water-retaining compounds) that are exploited economically. Agar, a commercial product derived from Gelidium and Gracilaria, cultivates bacteria and creates ice creams and jellies. A protein-rich unicellular alga, Chlorella, is utilised as a nutritional supplement by astronauts.

Conclusion

Algae are eukaryotic organisms that mostly thrive in moist places. The types of algae include red algae, brown algae and green algae. Blue-green algae are cyanobacteria that are prokaryotic and are hence not true algae. However, various algae are beneficial to human beings as they account for the most amount of photosynthesis on Earth.