The word "algae" refers to thallose, chlorophyllous plants that vary greatly in terms of physiology, biochemistry, habit, habitat, organization, and reproduction. Because their thallus contains a variety of pigments, they exhibit a range of colors, including blue-green, green, brown, red, and so on. Their food reserve consists of carbohydrates in one form or another, together with lipids and oils. Their cell wall is composed of real cellulose. They play a crucial role in the aquatic food chain and are highly valuable economically, contributing both positive and negative actions. Phycology, also known as Algology (phycos = seaweed, logos = discourse), is the study of algae.
The Classfication Followed This Book By is as given by G.M.Smith (1955)
General Characters Of Chlorophyta
He largest division of algae is called Chlorophyta. Because chlorophyll-a and chlorophyll-b predominate over carotenes and xanthophylls, members of the chlorophyta group are known as grass-green algae. Their habitat and habits show a wide range of differences.
Distribution
1.The members of Chlorophyta exhibit a wide range of distribution in aquatic (both water and marine) and terrestrial habitat.
2.Some of the fresh water algae form greenish scum on the surface of quiet, stagnant water (Volvox, Chlamydomonas, Spirogyra, Zygonema) or grow firmly attached to submerged rock, plant parts etc., in free flowing streams (Oedogonium, Cladophora, Chaetophorous, Collocate).
3. Marine algae are Caulerapa, Acetabularia, etc.
4. Terrestrial algae grow in moist damp soil, on shaded sides of rocks and bark of trees Trentepohlia, Pleuococcus). Several algae grow on snow (Scotiella).
5.Some algae have lost their pigments and become parasites on other plants causing serious diseases, for example, on tea and pepper plants (Cephaleuros), on Sphagnum moss (Phyllobium 6. Some grow ), etc.
Cell structure
1. The cell wall is a secretion product of protoplast and is made up of two layers; the outer one of of pectose while inner one is of cellulose. In some algae, outermost layer of pectose is converted into water soluble pectin which dissolves in surrounding medium. In Siphonales, callose is present instead of cellulose while in certain Volvocales, cell wall are absent
2. Internal to the cell wall is a living substance called protoplast. It is bounded bya living semipermeable, very thin plasma membrane which is three layered; the outer and inner are of proteins and middle one is of lipid. The cytoplasm is granular, viscous and often exhibits streaming movements.
3. Usually there is a conspicuous central vacuole of variable size bounded by definite tonoplast. The vacuole is traversed by cytoplasmic strands.
4.The nuclei are one to many and are of eukaryotic type, i.e., with nuclear membrane, nucleoplasm, nucleoli and with chromatin network.
5. Mitochondria, Golgi bodies, ribosomes and endoplasmic reticulum are present in algal cells.
6.Bacteria have two or four whiplash-type flagella that extend from the anterior end of their motile cells. Each flagellum has a single granule known as a blepharoplast at its base. Oedogonium cells that move have a ring of flagella and are Mult flagellate.
Sexual & Asexual Reoroduction
Sexual Reproduction
Its shape and amount of flagella are favorable. Zoospores are haploid, bi- or quadriflagellate, and cell wallless. Zoospores in Oedogonium are multiwavelet, with a ring of flagella. Any thallus green cell, with the exception of holdfast, can create zoospores through mitosis, or in specialized cells known as zoosporangia. Asexual reproduction occurs under unfavorable conditions when nonflagellated, thin-walled aplanospores, thick-walled hypnospores, or extremely thick-walled akinetes arise. (Some claim that Akinete is a vegetative.
Asexual Reproduction
It occurs through gamete formation. There are three types of gametic union: oogamous (male gamete is motile, called an antherozoid, and female gamete is a non-motile egg), anisogamous (fusing gametes are uneven in size), and isogamous (fusing gametes are equal in size). Conjugation is a primitive form of isogamous reproduction seen in algae such as Spirogyra and Zygonema.
Types Of Algae
Ulva: This alga is used for generation of biofuel. The predigestion of the Ulva extract is carried out. Hydrolysis of the juice results in production of methane gas, This methane gas can be used as biofuel.
Spirulina: It is a rich source of protein, minerals, fats, carbohydrate and vitamins and antioxidants. It is used as protein supplement in feeds of cattles and poultry. It is also used as a therapeutic agent in pharmaceutical industries. It provides large number of benefits at low cost of production. Thus it is economically very valuable of neutracentical
Gelidium: This algae is used to yield a highly economically important product. Agar- agar. Agar is a chemically inert with neutral pH. Agar is used in food industry and largely in scientific laboratories as a gelling agent for carrying out microbiological and tissue culture experiments.
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