Plant Kingdome - Algae | NCERT concept | Neet Concept | Biology

Plant Kingdome - Algae

• The earliest systems of classification used only gross superficial morphological characters such as habit , colour , number and shape of leaves etc. They were based mainly on vegetative characters or on the androecium structure . Such systems of classification were artificial . They separated the closely related species since they were based on a few characteristics .
• After that , natural classification systems were developed based on natural affinities among the organisms and consider not only the external features but also internal features such as , ultra structure , anatomy , embryology and phytochemistry . Such a classification for flowering plants was given by George Bentham and Joseph D. Hooker , popularly known as Bentham and Hooker classification system .
• Phylogenetic classification systems were developed based on evolutionary relationships between various organisms . • The Kingdom Plantae includes multicellular , eukaryotic , chlorophyll containing organisms . The plant cells have an eukaryotic structure with prominent chloroplasts and cell wall mainly made up of cellulose .
• According to traditional systems of classification , the Kingdom Plantae is divided into two subkingdoms : Cryptogamae and Phanerogamae . Cryptogamae ( plants without seeds ) is further divided into algae , bryophyta and pteridophyta , while phanerogamae ( plants with seeds ) is further divided into gymnospermae and angiospermae .

• Phylogenetic classification depicts the evolutionary relationships through a phylogram , phylogenetic tree or a cladogram . All the descendants of a common ancestor should be placed in the same group ( monophyletic group ) . If some descendants have been left out , they comprises paraphyletic group . The contemporary phylogenetic systems of classification includes Takhtajan , Cronquist etc.
• Classification not only helps in the placement of an entity in a logically organised scheme of relationships , it also has a great predictive value .

ALGAE

• Algae are chlorophyllous , simple , non - vascular , thalloid plants .
• As per Linnaeus ' two kingdom classification , all members of algae were grouped into plant kingdom along with bacteria and fungi .
• These are usually aquatic , either marine or freshwater , a few algae occur in moist terrestrial habitat .
• Algae are covered by mucilage which protects them from epiphytic growth and decaying effect of water and also prevents desiccation .
• Algae mainly contain chlorophyll a , carotenes and xanthophylls .
• Algae are usually classified on the basis of their pigments , flagellation and storage products .
• Most of algae are autotrophic . Some are parasitic ( Cephaleuros , Harveyella ) .
• Vegetative , asexual and sexual modes of reproduction are present .
• Vegetative reproduction may take place by fragmentation ( e.g. , Ulothrix , Oedogonium ) or by the formation of different types of spores .
• Asexual reproduction is by flagellated zoospores produced in zoosporangia In unicellular alga chlamydomonas , asexual reproduction also takes place by palmella stage . In palmella stage , a large number of near nacked cells devoid of flagella , lie inside a mass of mucilage . The stage develops in response to unfavourable water condition .

• Asexual reproduction takes place by flagellated zoospores ( e.g. , Ulothrix , Oedogonium ) ; non - motile , thin walled aplanospore ( e.g. , Chlorella , Microspora ) and non - motile , thick walled hypnospores ( e.g. , Vaucheria , Chlamydomonas nivalis ) , thick walled akinetes ( e.g. , Cladophora ) , palmella stage ( e.g. , Chlamydomonas ) .
• Sexual reproduction involves isogamy , anisogamy and oogamy in different groups
• Life cycle may be haplontic , diplontic or diplohaplontic .
• The algae are divided into three main classes - Chlorophyceae , Phaeophyceae and Rhodophyceae .

Importance of Algae

Food

• Certain algae are used as food e.g. , Porphyra , Laminaria , Sargassum , etc. , Chlorella is rich source of proteins , hence used as food supplement .

Photosynthesis :

• Nearly 50 % of total photosynthesis on earth is carried out by algae . They are essential for respiration of aquatic life .

Alginic acid :

• A phycocolloid obtained from phaeophyceae such as Laminaria , Macrocystis , Fucus , etc. , is used in stabilising emulsions , flameproof plastics and security glass .

Agar - agar

• A phycocolloid extracted from species of red algae such as Gelidium and Gracilaria is used as a solidifying agent in culture medium .

Carrageenan :

• Obtained from red algae Chondrus crispus and used as pharmaceutical emulsifier , cleaning agent and in textile , leather and brewing industries .

Medicines :

• Red algae Corallina is capable of curing worm infections . Brown algae Laminaria and Ascophyllum have antibiotic properties while Durvillea has vermifuge properties . Antibiotics are also extracted from green algae Chlorella and Caulerpa .

Sewage disposal :

• Green algae like Chlamydomonas , Chlorella , Scenedesmus are components of sewage oxidation tanks which provide aerobic conditions for disposal of sewage by decomposers .

Algae of unusual habitats

• Halophytic algae - Occur in saline sea water and salt lakes and can withstand high concentration of salts , e.g. , Chlamydomonas ehrenbergii , Stephanoptera .
• Epiphytic algae Grow on larger algae , bryophytes and angiosperms , e.g. , Oedogonium and Microspora are found attached to larger species of Vaucheria , Cladophora and Rhizoclonium .
• Epizoic algae - Grow on animals such as snails , fishes and tortoise , e.g. , Cladophora crispata ( epizoic on snail ) ..
• Endozoic algae - Occur in tissues of animals , e.g. , Zoochlorella in Hydra viridis .
• Cryophytic algae - Grow on ice or snow and impart attractive colours to snow covered mountains , e.g. , Haematococcus nivalis imparts red colour to alpine and arctic mountains while Chlamydomonas yellowstonensis and Mesotaenium species are responsible for green snow in Europe .
• Parasitic algae - Grow as parasites on many plants and animals , e.g. , Cephaleuros virescens causes red rust in tea and coffee plantations
• Thermophytes - Occur in hot water springs ( 50-70 ° C temperature ) as are able to survive high temperatures due to absence of well organised nucleus , e.g. , Oscillatoria brevis .

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