Algae: Meaning, Characteristics and More

Have you ever seen a green layer on a pond or on a moist area of a garden? This layer is Algae. It is known as the thalloid plant of the Plantae kingdom. They are also known as microscopic plants. The seaweeds and pond scums are the most common forms of algae. They could be unicellular or multicellular. These plants are primarily aquatic and can be found in freshwater, marine, moist surfaces of stone and wood and have a thalloid structure.

Algae are a class of organisms that are mostly aquatic, photosynthetic, and nucleus-bearing but lack the real roots, stems, leaves, and specialised multicellular reproductive systems that plants have. Continue reading to know more.

Algae Definition

The Latin word “Alga” means “Seaweed”. Algae are eukaryotic, autotrophic (holophytic), chlorophyll-containing, non-vascular thallophytes. These are characterised by the absence of embryonic stage and the presence of non-jacketed gametangia. Mostly, they are of aquatic habitat (both freshwater and marine). (Source: Arihant Biology Handbook).
‘Algology or Phycology’ is the branch of Botany that deals with the study of algae. FE Fritsch is known as ‘Father of Algology’.

Fig: Algae

Algae Characteristics

1. They are also called Thallophyta.
2. They include the plants which have undifferentiated, thalloid organisation.
3. Most forms of algae are aquatic. They may be marine (like Fucus, Sargassum, Laminaria, Ectocarpus, Dictyota, Polysiphonia, etc.) or freshwater (like Spirogyra, Volvox, Chlorella, Chlamydomonas, Batrachospermum, etc.). They are also found in terrestrial habitats in association with fungi to form Lichen.
4. They are eukaryotic, autotrophic, chlorophyllous, oxygenic-photosynthetic, and non-vascular cryptogams.
5. The plant body is gametophytic, haploid (Fucus is diploid), thalloid, which means without stem, leaf, root differentiation. Some may even have stem-like (stipe), root-like (holdfast), and leaf-like (assimilator) parts.
6. Root, stem, leaves and vascular tissues viz., xylem and phloem are totally absent in algae. Hence, the plant body of algae is referred to as a thallus.
7. Thallus may be:
a. Unicellular: motile (Chlamydomonas) or non-motile (Chlorella).
b. Multicellular:
i. Colonial – Volvox.
ii. Filamentous – Spirogyra, Zygnema, Ulothrix, Cladophora.
iii. Well-developed thallus – Chara.
iv. Parenchymatous – Ulva, Sargassum.
v. With holdfast, stipe, blade – Fucus, Dictyota, Laminaria.
8. They show a haplontic life cycle.
9. Embryo stage is absent in the life cycle.
10. They have unicellular sex organs, and the sterile jacket is absent on the sex organs.
11. They reproduce by vegetative, asexual, and sexual methods:
a. Vegetative mode of reproduction:
i. Fragmentation is found in filamentous forms.
b. Asexual mode of reproduction:
i. Zoospores are flagellated asexual spores formed that is responsible for their motility. They are formed in Chlamydomonas, Ulothrix, etc.
ii. Aplanospores are non-motile spores; otherwise, they resemble zoospores. They are formed in Chlorella.
iii. The Palmella stage is the large masses of usually immobile cells embedded in a gelatinous matrix of flagellated algae or plant-like flagellates. It is found in Chlamydomonas, Ulothrix, etc.
iv. Akinete is a thick-walled, non-motile, dormant cell derived from the enlargement of a vegetative cell. It is a resting cell of unicellular and filamentous green algae. It is found in Chara, Oedogonium, etc.
c. Sexual mode of reproduction:
i. Depending on the nature of gamete, sexual reproduction is of the three types:
a. Isogamy is found in Spirogyra, where male and female gametes are identical in morphology, and both are motile.
b. Anisogamy is found in Chlamydomonas, where the male and female gametes are motile, but male gametes are smaller and female gametes are larger.
c. Oogamy is found in Volvox. This is a type of anisogamy, but the female gametes are non-motile.

Fig: Different types of Sexual Reproduction found in Algae

12. They show mainly haplontic life cycles with zygotic meiosis. Fucus shows a diplontic life cycle.

Algae Classification

There are mainly three classes of algae, i.e. Chlorophyceae, Phaeophyceae and Rhodophyceae. They are explained below:

Fig: Chlorophyceae

Fig: Phaeophyceae

Fig: Rhodophyceae

Algae Examples

A few examples of algae are as follows:
1. Volvox: Chlorophyceae or Green algae
2. Chlorella: Chlorophyceae or Green algae
3. Laminaria: Phaeophyceae or Brown algae
4. Fucus: Phaeophyceae or Brown algae
5. Chlamydomonas: Chlorophyceae or Green algae
6. Spirogyra: Chlorophyceae or Green algae
7. Acetabularia: Chlorophyceae or Green algae
8. Polysiphonia: Rhodophyceae or Red algae
9. Porphyra: Rhodophyceae or Red algae
10. Chara: Chlorophyceae or Green algae
11. Ulva: Chlorophyceae or Green algae

Chromatic Adaptation in Algae

1. The vertical and horizontal distributions of red, green and brown algae are limited in part by the availability of sunlight and therefore vary by depth, latitude, sea conditions and season.
2. The vertical distribution of red, brown and green algae can be explained by their accessory photosynthetic pigments, which gives the seaweeds their characteristic colours, a concept known as Chromatic Adaptation.
3. Green algae, which have pigments mainly absorbing blue and red wavelengths that are diminished rapidly in seawater, found at the shallowest depths.
4. Blue-green light penetrates deepest in coastal waters and the accessory pigments of red algae absorb mostly green wavelengths, red algae extend to the greatest depth of primary producers.
5. The accessory pigments of brown algae absorb intermediate wavelengths of light; therefore, brown algae would be most abundant at intermediate depths.

Algae: Economic Importance

The economic importance of algae is mentioned below:
1. Algae being photosynthetic, are the essential producers of aquatic bodies, oceans, lakes etc.
2. Algae carry out \({\rm{50\% }}\) of the total \({\rm{C}}{{\rm{O}}_{\rm{2}}}\) fixation of the earth.
3. They provide food and oxygen for aquatic animals. Also, it increases the level of dissolved oxygen in the water.
4. Chlorella, a unicellular green alga, has a high vitamin B and protein content also used in space research.
5. Acetabularia, Chlorella, etc. are used in biological research programmes.
6. Laminaria, Fucus, Sargassum, etc. are used as food and fodder.
7. Antibiotic chlorellin is isolated from Chlorella.
8. Sea-weeds are very rich in minerals. Iodine and Bromine are extracted from marine algae.
9. Algae like Fucus, Macrocysts, Sargassum, etc., are used as manure.
10. These have good water holding capacity and high organic and mineral contents.
11. A microcyst produces toxins that are harmful to various microbes.
12. Carrageenan obtained from red algae are used as an emulsifying and stabilising agent in ice-creams, chocolates, cosmetics, toothpaste, etc., and as a pharmaceutical emulsifier, textile, leather and brewing industries.
13. Algin is extracted from the cell wall of brown algae. Algin is used in preventing the formation of crystals in ice-creams. It is also used to stop bleeding. It finds a place in the preparation of soups, creams, sauces, etc. Algin is also helpful in paint, pigment and rubber processing, pharmaceutical automobile polish industries, and dentistry to take dental impressions.
14. Agar, extracted from the members of Rhodophyceae like Gelidium and Gracilaria. Agar is used as a base for culturing bacteria, algae, fungi in the laboratories and tissue culture. It is also used in the baking and confectionery industry as an emulsifying agent and food, cosmetics, textile, leather, paper and pharmaceutical industries.

Difference Between Algae and Fungi

The difference between Algae and Fungi are given below:

Summary

Algae are the smallest living organisms of Plant Kingdom. They are mainly aquatic and are found in marine, freshwater, and moist places. These are both unicellular and multicellular organisms. Algae can be classified into three classes Chlorophyceae, Phaeophyceae and Rhodophyceae. The reproduction in these plants is vegetative, asexual, and sexual methods. Algae are eukaryotes and autotrophic. Though they are not such familiar plants, their importance is very significant as some algae are used in space and biological research.

Frequently Asked Questions

Q.1: Write five general characteristics of algae?
Ans: (a) They include the plants which have undifferentiated, thalloid organisation.
(b) They are eukaryotic, autotrophic, chlorophyllous, oxygenic-photosynthetic, and non-vascular cryptogams.
(c) The plant body is gametophytic, haploid, thalloid, which means without stem, leaf, root differentiation.
(d) They have unicellular sex organs, and the sterile jacket is absent on the sex organs.
(e) There is no vascular tissue in these plants.

Q.2: Write \(4\) examples of algae?
Ans: The \(4\) examples of algae are Volvox, Spirogyra, Chlamydomonas, Chlorella, Ulothrix, etc.

Q.3: Write the difference between red algae and brown algae?
Ans: 1. Red algae are grouped under the class Rhodophyceae, whereas brown algae are grouped under the class Phaeophyceae.
2. Red algae contain floridean starch as stored food, whereas brown algae contain mannitol and laminarin as stored food.
3. Red algae contain the photosynthetic pigments chlorophylls a and d, and phycoerythrin and phycocyanin, whereas brown algae contain the photosynthetic pigments chlorophylls a and c, and fucoxanthin.

Q.4: What are algal blooms?
Ans: Algal bloom is a rapid increase in the population of algae in an aquatic system. These are caused due to eutrophication,i.e.excess nutrients into water bodies.

Q.5: Why are algae important?
Ans: Algae are the most important producer of photosynthesising organisms on Earth. They form the energy base of most aquatic food webs which support an abundance of animals. They convert water and carbon dioxide to sugar and oxygen through the process of photosynthesis.