Biology XI:3.Plant Kingdom(1 Division Algae)

Division Algae Classification within Angiosperms Artificial system of classification Given by Linnaeus Based on vegetative characters and androecium structures Gave equal importance to vegetative and sexual characteristics Natural system of classification Based on morphology, anatomy, embryology, and phytochemistry Given by George Bentham and Joseph Dalton Hooker Phylogenetic system of classification - based on evolutionary relationship Numerical Taxonomy Based on all observable characteristics Numbers and codes assigned to all characters Easily carried out using computers Cytotaxonomy − Based on cytological information such as chromosome number, structure, behaviour Chemotaxonomy − Based on chemical constituents of plant to resolve doubts and confusions Division Algae Includes chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic (freshwater and marine) organisms Some occur in association with fungi (lichens) and animals (on sloth bear). Size ranges from microscopic unicellular forms such as Chlamydomonas to colonial forms such as Volvoxand to filamentous forms such as Ulothrix and Spirogyra. Massive plant-like bodies are seen in some marine forms (such as kelps). Economic Importance Carbon dioxide fixation on earth is majorly carried out by algae. Important as primary producers of energy-rich compoundsExample − Sargassum, Laminaria, and Porphyra used as food Some brown and red algae species produce water-holding hydrocolloids.Example − Algin (brown algae) and carrageen (red algae) Agar produced by Gelidium and Gracilaria is used to grow microbes and in preparation of ice creams and jellies. Chlorella and Spirulina are protein-rich unicellular algae, used as food supplements. They are also known as space food. Major classes of algae: Chlorophyceae Commonly called green algae May be unicellular, colonial, or filamentous Grass green in colour due to abundance of chlorophyll a and b Chloroplast of most of the Chlorophyceae contains pyrenoids. Pyrenoids − Storage bodies containing proteins in addition to starch Food storage occurs in the form of oil droplets in some algae. Cells have rigid cell wall: inner layer made of cellulose, outer layer made of pectose Phaeophyceae (Brown algae) Primarily marine forms Show great variation in size and form Range from simple-branched, filamentous forms (Ectocarpus) to profusely branched forms such as kelps (may reach a height of 100 m) Possess chlorophyll a, c, carotenoids, and xanthophylls Vary in colour from olive green to various shades of brown (depending on amount of xanthophyll and fucoxanthin) Food stored as complex carbohydrates such as laminarin or mannitol Vegetative cells have cellulosic wall covered on the outside by gelatinous coating of algin. Cell contains a centrally located vacuole and nucleus in addition to plastids. Union of gametes takes place in water or within oogonium (oogamous species). Gametes are pyriform (pear-shaped).Example − Ectocarpus, Dictyota, Laminaria, Sargassum, and Fucus Rhodophyceae (Red algae) Commonly called red algae due to the presence of red pigment, r-phycoerythrin Mainly marine forms with bulk mass inhabiting warmer areas Occur in well-lighted regions i.e., close to the surface of water and also in deeper areas Red thalli of most of these species are multicellular. Some have complex body organization. Food is stored as Floridian starch similar to amylopectin and glycogen in structure Example − Polysiphonia, Gelidium, Gracilaria, Porphyra