Plant Kingdom (Biology)
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).
* Carbon dioxide fixation on earth is majorly carried out by algae. * Important as primary producers of energy-rich compounds Example − 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:
* 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
* Known as amphibians of plant kingdom since they live on land, but depend on water for sexual reproduction *...
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