Algae 

Algae are a diverse group of simple, autotrophic, photosynthetic organisms that belong to the Algae Kingdom (Thallophyta) under the Plant Kingdom. In simple terms, Algae meaning refers to plant-like organisms that can make their own food through photosynthesis but lack true roots, stems, and leaves. Algae are primarily aquatic, thriving in freshwater, marine, and moist terrestrial environments. They form the base of aquatic food chains and contribute significantly to the production of atmospheric oxygen. Although many people associate algae with “pond scum” or “seaweed,” they play an essential role in maintaining life on Earth — serving as primary producers, oxygen sources, and food for aquatic life.

1.0General Characteristics of Algae

• Algae are found in both fresh and marine water. Algae are found in many forms, like filamentous (Ulothrix and Spirogyra), colonial (Volvox), and microscopic unicellular form like Chlamydomonas, and a few of the marine forms like Ulothrix and Spirogyra.
• A few of the marine forms, such as kelps, form massive plant bodies.
• A mucilaginous sheath surrounds algae, and below the sheath, the cell wall is present, which is made up of cellulose, galactans, mannans and minerals.
• The body of algae is thallus-like (thalloid), i.e., the plant body is not differentiated into leaves, stems, and roots.
• Based on nutrition, algae are photoautotrophic (Oxygenic phototrophs). They have a plastid containing photosynthetic pigments.
• The plant body of most algae is made of haploid cells.
• Algae are non-vascular plants, meaning they lack vascular tissues.

2.0Economic Importance of Algae :

Algae are helpful to man in a variety of ways :

• Chlorella, a unicellular alga rich in protein is used as a food supplement even by space travellers.
• Many species of Porphyra, Laminaria and Sargassum are among the 70 species of marine algae used as food.
• Certain marine brown and red algae produce large amounts of hydrocolloids (water-holding substances), e.g., Algin (brown algae) and Carrageen (red algae) are used commercially.
• Gelidium and Gracilaria - Agar-Agar is a hydrocolloid (water-holding substance) obtained from these red algae. It is used to prepare culture medium for growing microbes and to prepare ice creams and jellies.
• Alginates or Alginic acid - Obtained from Laminaria, Fucus and Macrocystis and used for denture measurement, polishing and manufacturing of soap, ice-creams.
• Iodine and Bromine are both obtained from Laminaria.
• At least half of Earth's total carbon dioxide fixation is carried out by algae through photosynthesis. As photosynthetic organisms, they increase the dissolved oxygen level in their immediate environment.
• They are of paramount importance as primary producers of energy-rich compounds, which form the basis of the food cycles of all aquatic animals.

3.0Algae - Classes (Chlorophyceae, Phaeophyceae and Rhodophyceae) :

Algae are divided into the following classes

(A) CHLOROPHYCEAE – Green algae

(B) PHAEOPHYCEAE – Brown algae

(C) RHODOPHYCEAE – Red algae

(A) CHLOROPHYCEAE (GREEN ALGAE) :

• They are usually green due to the dominance of pigments chlorophyll a and b.
• Green algae are the most advanced algae. It is believed that green algae are the ancestors of the higher plants.
• Habitat: Green algae are cosmopolitan and occur in fresh, brackish, and saline waters.
• Structure: Green algae typically have a rigid cell wall composed of an inner layer of cellulose and an outer layer of pectin.

Green algae are found in many forms:

(i) Unicellular:-

e.g. Chlamydomonas - Motile unicellular algae. These algae move using flagella.

Chlorella – non-motile algae

(ii) Colonial:-

e.g. Volvox - Motile colony

(iii) Multicellular filamentous:- Mostly the green algae are multicellular and filamentous.

e.g. Ulothrix, Spirogyra

(B) PHAEOPHYCEAE (BROWN ALGAE) :

Brown algae, seaweeds, or Kelp

• Habitat: The members of Phaeophyceae are found primarily in marine habitats.
• Structure: Brown algae show significant variation in size and form. They range from simple branched, filamentous forms (Ectocarpus) to profusely branched forms like Kelps.
• Brown algae are the largest in size (up to 100 meters in length).
• The plant body is usually attached to a substratum by a holdfast and has a stalk (stipe) and leaf-like photosynthetic part, frond or lamina, so brown algae are also known as leafy algae. (e.g. Laminaria)
• The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin. In brown algae, the protoplast contains a plastid, a centrally located vacuole and a nucleus. e.g. Fucus, Dictyota, Ectocarpus

(C) RHODOPHYCEAE (RED ALGAE) 

• Commonly called red algae because of the predominance of the red pigment r-Phycoerythrin in their body.
• Red algae are ancient (Primitive) algae. e.g. Polysiphonia
• There is no motile stage found in the life cycle of red algae, i.e. cilia & flagella are absent.
• Some of them have complex body organisation.
• Habitat: The Majority of red algae are found in marine water, with higher concentrations in warmer areas.
• Structure: The red thalli of the red algae are multicellular.
• The cell wall is made up of cellulose and pectin, and polysulfate esters.
• Red algae occur in both well-lit regions near the surface of the water and at great depths in the ocean, where relatively little light penetrates.

4.0CLASSES OF ALGAE AND THEIR MAIN CHARACTERISTICS