ALGAE

Eukaryotic, multicellular, chlorophyll containing organisms having cell wall, are grouped into the kingdom Plantae, popularly known as plant kingdom.

Phylogenetic system of classification based on evolutionary relationship is presently used for classifying plants.

Numerical Taxonomy use computer by assigning code for each character and analyzing the features.

Cytotaxonomy is based on cytological information like chromosome number, structure and behavior.

Chemotaxonomy uses chemical constituents of plants to resolve the confusion.

The Plant kingdom is divided into Cryptogams (Plants without seeds) and Phanerogams (Plants with seeds). The cryptogams include Thallophyts, Bryophyts and Pteridophyts. The Phanerogams include Gymnosperms and Angiosperms.

Thallophyts- the Thallophyts Comprise the simplest plants which possess undifferentiated or thallus like plant body. It includes only Algae.

                            ALGAE

Algae are chlorophyll bearing simple thallophytic organisms as well as there colourles derivatives that fail to reach the level of differentiation characteristic of archegoniate plants.

Characteristic of Algae

Habit and habitat;- Algae are mostly aquatic but a few are also found in moist terrestrial habitats like tree trunks, rocks, moist soil etc. These are dominant in stagnant waters. The free floating assemblage of algae is called phytoplanktons. Some algae are endophytes some are epiphytes and some form the symbiotic associations.

Thallus structure:- as per there structure is concerned these are of the following types;

Motile forms;- these forms bear flagella so are motile. Some motile forms like chlymydomonas are unicellular bearing two flagella at anterior end. Some form like Gonium consist of definite number of cells in a gelatinous matrix. In some motile forms the indefinite no. of cells are contained in a gelatinous sheath forming a colony. Such forms are called colonial (volvox).

Non-motile or cocoid forms. This group comprises non-flagellated algae. Some unicellular algae like chlorococum are unicellular and some forms like hydrodictyon are coenobial.

Palmeloid or dendroid forms:- these include algae that are non-motile but develop flagella at the time of reproduction (ecbalocystopsis)

Filamentous:- in some algae the cell division occurs in only one plane which gives rise to long filaments. The filamentous algae can be branched (cladophora) unbranched (zygnema) or falsely branched (sytonema)

Siphonaceous habit:- the algae that are non septate, multinucleate, and coenocytic are said to exhibit siphoneceous habit. (vaucheria).

Reproduction

Vegetative:- the algae reproduce vegetatively by fragmentation (oscillatoria) or by cell division. Some also divide by binary fission.

Asexual:- in algae the asexual reproduction occurs by the formation of spores. The spores are cells which develop into new individuals without fusion. The various types of spores formed in algae are

Zoospores;- these are motile spores that are produced from the vegetative cells inside zoosporangium. The zoospores that are produced after meiosis are called meiospores, and those which are produced after mitosis are called mitospores.

Aplanospores;- these are non-motile spores but bear the capacity to develop flagella.

Autospores;- these spores are same as aplanospores but lack the capacity to develop flagella.

Hormospores;-  hormospores are the fragments of some filamentous algae that develop into new forms.

Heterocysts;- these are large vegetative cells and act as the points of fragmentation(nostoc)

Akinetes;- these are vegetative cells that develop into spore like forms with thick walls and abundant food.

Sexual reproduction;- sexual reproduction in algae occurs by the fusion of two gametes which may be morphologically and physiologically similar- Isogamy (Spirogyra), dissimilar (large female gamete and smaller male gamete)- Anisogamy (Chlamydomonas) or Oogamous- large non motile egg and small motile sperm  (Volvox).

In algae the Vascular tissues and mechanical tissues are absent.

Economic importance-

• A number of brown algae ( Laminaria, Sargassum) are used as food in some countries.
• Fucus and Laminaria are rich source of Iodine.
• Laminaria and Ascophyllum have antibiotic properties.
• Alginic acid is obtained from Fucus and Sargassum, which is used as emulsion.
• Marine brown algae (Algin) and red algae (Carrageen) are used as Hydrocolloids, which is a fibrous structure holds water and used to transport seedling.
• Gelidium, Graularia are used to grow microbes, make ice creams and jellies.
• Chlorella and Spirullina are rich in proteins and used as food supplements.

CLASSIFICATION OF ALGAE

The term algae was coined by c. linneus. The algae are divided on the basis of set of seven characters.;

1- Type of photosynthetic pigments, 2- nature of food reserves 3-cell wall components, 4- number of flagella, 5- nature of eye spot 6- nuclear composition 7- cell structure.

The different algal classes along with their important features are given in the table:-

Class of algae	Common name	Pigments	chloroplast	Cell wall	Food reserves	Flagella	Example
Cyano- phyceae	Blue green algae	Chl.-a, b carotene, phycocyanin	Absent	Four layered (peptidoglycan)	Phycocyanin	Absent	Oscillatoria, nostoc
Chloro-phyceae	Green algae	Chl.-a,b αβδ-carotene,	Present (thalakoids)	Cellulosic	Starch	Two equal	Chlorella, gonium, volvox
Rhodo-phyceae	Red algae	Chl.-a,d αβ-carotene, phycoerythrin	Present	Cellulosic	Floridean starch	Absent	Porphyra, batrachospermum
Xantho-phyceae	Yellow green algae	Chl.-a, β-carotene, diatoxanthin	Present	Cellulosic	Fats/oils	Two-heterokonte	Botrydium, vaucheria
Phaeo- phyceae	Brown algae	Chl.-a,c β-carotene, fucoxanthin	Present	Cellulosic	Laminarin	Two-equal	Padina, laminaria
Eugleno-phyceae	Euglenoids	Chl.-a,b β-carotene, astaxanthin, neoxanthin	Present	Protenaecious (pellicle)	Paramylon/glucan	Two-unequal	euglena