Title Med-RM_Bot_SP-2_Ch-7-Plant Kingdom.pdf ✅

Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents Chapter 7 Classification Systems Branches of Taxonomy Algae Bryophytes Pteridophytes Gymnosperms Angiosperms Plant Life Cycles and Alternation of Generations The plant kingdom has been classified in various ways by different scientists. Here, we will describe Plantae under Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms. CLASSIFICATION SYSTEMS There are three main types of systems of classification, i.e., artificial, natural and phylogenetic. Artificial System of Classification (a) Basis : The earliest systems of classification were artificial and involves usage of one or few morphological characters for grouping of organisms. For example, classification within the angiosperms was based only on morphological characters such as habit, colour, number and shape of leaves or on the androecium structure (system given by Linnaeus). (b) Proponents - Aristotle and Linnaeus. (c) Drawbacks : (i) They separated the closely related species. (ii) Also equal weightage to vegetative and sexual characteristics were given. Since the vegetative characters are more affected by environment, so this was not acceptable. Natural System of Classification: (a) Basis : Organisms are classified on the basis of natural affinities and consider not only external but also internal features like ultrastructure, anatomy, embryology and phytochemistry. (b) Proponents : George Bentham and Joseph Dalton Hooker. Plant Kingdom
2 Plant Kingdom NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Phylogenetic System of Classification (a) Basis : At present phylogenetic classification systems are acceptable which are based on evolutionary relationships between the various organisms, assuming that organisms belonging to the same taxa have common ancestor. The fossils play important role in elucidation of evolutionary relationships. (b) Proponents : Engler and Prantl, Hutchinson, Takhtajan We now use information from many other sources too to help resolve difficulties in classification. These become more important when there is no supporting fossil evidence. BRANCHES OF TAXONOMY Numerical Taxonomy (Phenetics) : It involves usage of numerical methods for the evaluation of similarities and differences between species with the help of computers. Steps involved in numerical taxanomy : 1. Numbers and codes are assigned to all the observable characters like plus (+), minus (–), data not available (0). 2. All possible characters are compared by computers by giving equal importance. 3. The organisation and analysis of data forms core of this taxonomy. One of the major benefits of this taxonomic method is that hundreds of characters can be considered at the same time. Cytotaxonomy / karyotaxonomy : It is based on cytological information like chromosome number, structure, behaviour, etc. Chemotaxonomy : It is based on the chemical constituents of the plant. For example DNA sequence, chemical nature of proteins, crystals (Calcium oxalate or calcium carbonate) and aromatic compounds are used by scientists to resolve confusions in classification. ALGAE (Father of algology : F. E. Fritsch) Algae are chlorophyll containing, simple, thalloid (plant body not differentiated into root, stem and leaf) and autotrophic organisms. The main characteristics of algae are: 1. Algae are largely aquatic, either marine or fresh water. They also occur in habitats like moist stones, soils and wood. Some of them also occur in association with fungi (lichen) and animals (e.g., on sloth bear). 2. Algae are of variable size and forms. The size ranges from the unicellular (Chlamydomonas), colonial (Volvox), filamentous kelps to massive plant bodies (Ulothrix and Spirogyra). 3. Vascular tissues are absent. 4. Algae reproduce by vegetative, asexual and sexual methods. 5. Vegetative reproduction is by fragmentation. In fragmentation, the parent body breaks into two or more fragments which develops into a thallus. 6. During the asexual reproduction different types of spores are produced. Spores are released from the parent body which, on germination give rise to new plants. The most common spores produced are the flagellated (motile) zoospores.
NEET Plant Kingdom 3 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 7. Sex organs are non-jacketed and unicellular. Sexual reproduction can be : (i) Isogamous : Fusion of two gametes which are similar in size, either flagellated or non-flagellated is termed as isogamous., e.g., Ulothrix (gametes are flagellated and similar in size), Spirogyra (gametes are non-flagellated and similar in size). (ii) Anisogamous : Fusion of two gametes which are dissimilar in size is termed as anisogamous. e.g., Eudorina. (iii) Oogamous : When a small, motile or non-motile male gamete fuses with a large non-motile female gamete, such type of reproduction is known as oogamous., e.g., Volvox, Fucus, Polysiphonia (both gametes non-motile) Algae are mainly classified on the basis of their pigments. Flagellation, storage products and chemistry of cell wall are also taken into account. The three classes of algae are Chlorophyceae (green algae), Phaeophyceae (brown algae) and Rhodophyceae (red algae). Chlorophyceae 1. The pigments, chlorophyll-a, chlorophyll-b, carotene and xanthophyll are present in them. They are usually grass green in colour due to the dominance of pigments, i.e., chlorophyll a and b. 2. These pigments are present in definite chloroplasts. The shape of chloroplast varies in different species. It can be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped. 3. The plant body may be unicellular, colonial or filamentous. 4. Most of the green algae have one or more storage bodies called pyrenoids located in the chloroplasts. Pyrenoids contain protein and starch. In some food is stored in the form of oil droplets. 5. Green algae usually have a rigid cell wall made up of an inner layer of cellulose and an outer layer of pectose. 6. Vegetative reproduction by fragmentation. 7. Asexual reproduction takes place by zoospores produced inside the zoosporangia. Zoospores have 2- 8, apically inserted isokont flagella. 8. Sexual reproduction may be isogamous, anisogamous or oogamous. 9. Some commonly found green algae are : Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara. Daughter colony Parent colony (a) (b) Fig. : Green algae (a) Volvox, (b) Ulothrix
4 Plant Kingdom NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Phaeophyceae 1. Brown algae are found primarily in marine habitats. 2. They possess the pigment chlorophyll a and c, carotenoids and xanthophylls. 3. They vary in colour from olive green to various shades of brown depending upon the amount of the xanthophyll called fucoxanthin. 4. They show great variation of size and form. In Ectocarpus the body is simple branched and filamentous whereas in kelps the body is profusely branched e.g., Laminaria, Macrocystis. Kelps may reach a height of 100 metres. 5. Food is stored as complex carbohydrates which may be in the form of laminarin or mannitol (alcoholic sugar). 6. Brown algae have cell wall made up of cellulose which is usually covered on the outside by a gelatinous coating of algin. Algin is a hydrocolloid which has good water holding capacity. 7. Their protoplast contains plastids, a centrally located vacuole and nucleus. 8. The plant body is often differentiated into holdfast for attachment to a substratum, stipe (stalk) and leaf-like photosynthetic organ called frond. 9. The large forms often possess air bladders for providing buoyancy. 10. Vegetative reproduction takes place by fragmentation. 11. Asexual reproduction occurs with the help of biflagellate zoospores that are pear-shaped and have two unequal laterally attached flagella. 12. Sexual reproduction may be isogamous, anisogamous or oogamous. Fusion of gametes takes place in water but in oogamous species, gametes fuse in the oogonium. Oogonium is the female reproductive structure, usually a rounded cell or sac containing egg cell or oosphere (the non-motile female gamete). 13. The gametes are pyriform i.e., pear-shaped and bear two laterally attached flagella. 14. The common forms of brown algae are Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus. Frond Stipe Holdfast Holdfast Frond Midrib Air bladder Frond Stipe (a) (b) (c) Fig. : Brown algae : (a) Laminaria, (b) Fucus, (c) Dictyota Rhodophyceae 1. The pigments present in them are r-phycoerythrin, r-phycocyanin, chlorophyll-a and chlorophyll-d. The characteristic red colour is due to the predominance of the red pigment, r-phycoerythrin. 2. They are mostly found in marine habitats with abundance in the warmer areas.