Algae

Algae - Classification, Life cycle and Uses

The word algae address a large diversity of eukaryotic organisms ranging from unicellular microalgae to multicellular organism such as giant kelp. In general, algae are plant-like organisms that are subdivided into two parts photosynthetic and aquatic. Although it is a plant like organism, still it does not have true roots, stems, leaves, and vascular tissue but possess the simple reproductive structures. Algae or their spores can be found in a variety of environments such as fresh water, marine water, air, soil, or on other organisms. Majority of the variety of algae found are microscopic, yet some variety is found to be very large, such as marine seaweeds which can grow upto 50m in length. They are subdivided into two parts: Microalgae and other is Macroalgae.

  • 1. Microalgae: It is the unicellular form of algae.

  • 2. Macroalgae: It is the multicellular form of algae.


  • Microalgae are the photosynthetic, heterotrophic organisms which have an extraordinary potential for cultivation as energy crops. Algae have its nature that it can grow or can be cultivated under any difficult climatic conditions. Algae produce various commercial by-products such as fats, oils, sugars, and other useful bioactive compounds. The term also includes some members of the red, brown and green algae. They are photosynthetic in nature and "simple" because they don’t possess the bunch of complicated organs as found in land plants. Hence they are excluded from being considered as plants. 
    The algae possess chlorophyll in its structure which is responsible for the manufacturing of their own food by the photosynthesis process within the membrane bound structure called the chloroplasts. Almost all the algae are eukaryotes except the Cyanobacteria (which is a bacterial organisms traditionally included as algae), which possess a prokaryotic cell structure. Algae are extremely important species. They produce highest amount of oxygen as compared to all the living land plants in the world as well as they are also an important food source for many animals such as little shrimps and huge whales. Thus, they are at the bottom of the food chain because many living organisms are dependent on them.


    Recent research has proved that the algae can use for producing Biodiesel, which possess certain advantages like biofuel of algae is non-toxic, contains no sulphur, and is highly biodegradable. Moreover, they are high yielding as compared to other energy crops. The estimates suggest that microalgae are capable of producing up to 15,000 gallons of oil per hectare a year. This oil can be converted into fuels and chemicals and more. They can provide much higher yields of biomass and fuel, 10-100 times higher than comparable any energy crops. Also, they have the potential to grow under any conditions which may be unsuitable for conventional crop production. Micro-algae have the capacity to reduce atmospheric CO2 levels, thus fixing the increasing percentage of CO2 in the atmosphere, responsible for the global pollution problem.


    Classification of algae:


    Taxonomic classification of algae is based upon the same rules that are used for the classification of land plants. Microscopic research has shown differences in the features of algae which contributes to another method of their classification. Various features that differentiate various types of algae are: organelle structure, flagellar apparatus, and cell division process. Division-level classification (kingdom-level classification) is negligible for algae. Some scientists place class like xanthophycaecae, bacillophyceae, in division Chromophyta, whereas some scientists place each class in the division: xanthophyte, bacillophyta.

    In general and widely accepted terms, the classification of algae is done based on the following six types:

  • 1. Nuclear organization – prokaryotic or eukaryotic

  • 2. Nature of cell wall – cellulosic or non-cellulosic (protein, acid, polysaccharide)

  • 3. Pigmentation and Photosynthetic apparatus – 3 pigments (chlorophylls, carotenoids, and biloproteins)

  • 4. Nature of reserve food – Starch, oil, mannitol, leucosine etc. are the various types of reserve food in various classes.

  • 5. Flagellation – Type, number and position of flagella determines the class.

  • 6. Type of life cycle – complete absence or presence and the complexity of cycle.



  • Properties of algae:


    Different algae have different requirements. Hence, several essential factors such as water, carbon dioxide, minerals and light play important roles in the cultivation of the algae. 

  • Size and Structure

  • For single-celled algae, thallus is the body of the vegetative form of algae and for multi-celled algae; the thallus consists of the entire, continuous organism. The thallus is an example of complex algae, which appears to be macroscopic, and multicellular organism but is one giant, unicellular structure only. The aquatic habitat is a relatively benign and uniform place, which helped the organisms to get into shape. Because water supports the algal plant body, they easily flow with the water currents and waves. Since water surrounds the plant on all sides, individual algal cells absorb moisture (water), minerals and sunlight directly from the surrounding. Mostly they are photosynthetic in nature, possess four different kinds of chlorophyll pigments (include blue, red, brown, golden) maybe microscopic and float in the surface waters (phytoplankton) or macroscopic and live attached to rocky coasts (seaweeds). Size ranges from size of bacteria (0.5 µm) to over 50 m long. 

  • Temperature The temperature of the water must be in range that will support the growth of specific algal species. Temperature plays a major role in the growth of any algal species. The optimal temperature for phytoplankton cultures is between 20-30º C. If the temperatures is <16 º C it slows down the growth and a temperature >35 º C is lethal for a number of species.


  • Light

  • A light which is very strong or very low hinders the algae growth. In most algal-cultivation systems, light only penetrates the top 3 - 4 inches of the water. As the algae grow and multiply vigorously and become dense, they block light penetration into pond, tank etc. the light required by algae is only 1/10th of sunlight received by other plants. Direct and strong sunlight is harmful and destroys the growth of algae.

    Where do Algae Grow?


    The habitat of algae can be anywhere and everywhere. Algae are the most robust organism in terms of habitat, as they can grow in a wide range of conditions. Algae can be found in both environments: terrestrial and aquatic. Moreover, it’s very common to find algae in moist regions than dry ones, as algae do not have vascular tissues and other adaptations for living on land. Yet algae can be found in any and every part of the world. The examples include snails, turtles, worms, rotifers, worms, alligators, three-toed sloths, aquatic ferns, freshwater sponge, aquatic plants, on and inside water plants.

    The chemical composition of algae:


    Algae are comprised of two types of cell: eukaryotic or prokaryotic cell. These are cells with nuclei and organelles. The functional systems of algae are plastids, which are bodies with chlorophyll and carry out photosynthesis. Some have only Chlorophyll A, some A and B, A and C etc.the primary composition of algae is made up of proteins, carbohydrates, fats, nucleic acids, in varying proportion. All types of algae found completely comprise of the following, in varying proportions: Proteins, Carbohydrates, Fats and Nucleic Acids. While the percentages vary with the type of algae, types of algae are there, some of them comprised up to 40% of their overall mass by fatty acids. This fatty acid from the algae can be extracted and converted into biodiesel. Algal-oil is very high in unsaturated fatty (UFA) acids which include Arachidonic acid (AA), Eicospentaenoic acid (EPA), Docasahexaenoic acid (DHA), Gamma-linolenic acid (GLA), Linoleic acid (LA) etc.

    Lifecycle of Algae:


    Four main patterns of lifecycle in the algae are:

  • 1. Haplotonic lifecycle –The plant body is a gametophyte. The gametophytic plant produces haploid gametes. The gametes fuse to form a zygote, which is a diploid. Thus, diploid represents the sporophytic phase (diploid phase) of their lifecycle. This lifecycle is also known as monogenic lifecycle and is found to be active in a majority of classes.


  • 2. Diplotonic lifecycle – The plant body is a sporophyte. The sex organs produce gamete by meiosis, and they represent the gametophytic stage. The gametes soon unite and fertilize to form a zygote. The zygote does not undergo any meiosis. The zygote is only responsible to give rise to new sporophytic plant body.


  • 3. Diplohaplontic lifecycle – In this type, both the diploid and haploid phases are equally present and prominent, expressed by two distinct vegetative individuals. There is a difference in both only in terms of chromosome numbers and functions. The diploid (sporophytic stage) reproduces by asexual process, while the haploid (gametophytic stage) reproduces by the sexual method. This kind of lifecycle has two types: isomorphic (homologous) and heteromorphic (heterologous).


  • 4. Triphasic lifecycle – In this type, there is a succession of three distinct generations. This type of lifecycle has two types: Haplobiontic and diplobiotonic type.



  • Use of algae:


    Algae are used in various fields such as in the food industry as a food supplement, in waste-water purification as a bio-filter, in laboratory research system, in space biotechnology, etc. Algae are commercially cultivated for pharmaceuticals, nutraceuticals, cosmetics and aquaculture purpose. It is also used as a fuel source, stabilizing agent and as a fertilizer.