Title 3 plant kingdom-sample notes.pdf ✅

© www.bankofbiology.com All rights reserved. 1 Systems of Biological classification 1. Artificial classification systems - Earliest systems of classification. - They were based on vegetative characters or superficial morphological characters such as habit, colour, number and shape of leaves, etc. - Linnaeus’s artificial system of classification was based on the androecium structure. Drawbacks: - They separated the closely related species since they were based on a few characteristics. - Equal weightage to vegetative and sexual characteristics. This is not acceptable since the vegetative characters are more easily affected by environment. 2. Natural classification systems - These are based on natural affinities among organisms. - It considers external features and internal features (ultrastructure, anatomy, embryology & phytochemistry). - E.g. Classification for flowering plants given by George Bentham & Joseph Dalton Hooker. 3. Phylogenetic classification systems - It is based on evolutionary relationships among organisms. - This assumes that organisms in the same taxa have a common ancestor. Other sources to resolve the problems in classification: o Numerical Taxonomy: It is based on all observable characteristics. It is easily carried out using computers. Number & codes are assigned to all the characters and the data are processed. Thus, hundreds of characters can be equally considered. o Cytotaxonomy: It is based on cytological information like chromosome number, structure, behaviour etc. o Chemotaxonomy: It uses chemical constituents of plants. ALGAE - Algae are simple, thalloid, autotrophic, chlorophyll- bearing and aquatic (fresh water & marine) organisms. - They also occur in moist stones, soils and wood. - Some occur in association with fungi (lichen) and animals (e.g., on sloth bear). - The form and size of algae is highly variable. o Microscopic unicellular forms: E.g. Chlamydomonas. o Colonial forms: E.g. Volvox. o Filamentous forms: E.g. Ulothrix and Spirogyra. Reproduction: - Vegetative reproduction: By fragmentation. Each fragment develops into a thallus. - Asexual reproduction: By the production of spores. E.g. zoospores (most common). They are flagellated (motile) and on germination gives rise to new plants. - Sexual reproduction: Through fusion of two gametes. It is many types: o Isogamous: Fusion of gametes similar in size. They may be flagellated (e.g. Ulothrix) or non-flagellated (non-motile, e.g. Spirogyra). o Anisogamous: Fusion of two gametes dissimilar in size. E.g. Some species of Eudorina. o Oogamous: Fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete. E.g. Volvox, Fucus. Benefits of algae: ☺ Through photosynthesis, they fix half of the total CO2 on earth and increase the level of dissolved oxygen. ☺ They are primary producers and the basis of the food cycles of all aquatic animals. ☺ Many marine algae (70 species) are used as food. E.g. Porphyra, Laminaria and Sargassum. ☺ Agar (from Gelidium & Gracilaria) is used to grow microbes and in ice-creams and jellies. ☺ Some marine brown & red algae produce hydrocolloids (water holding substances). E.g. algin (brown algae) and carrageen (red algae). These are used commercially. ☺ Protein-rich unicellular algae like Chlorella & Spirulina are used as food supplements by space travelers. Algae include 3 classes: Chlorophyceae, Phaeophyceae and Rhodophyceae. 1. Chlorophyceae (green algae) - Unicellular, colonial or filamentous. - They are usually grass green due to the pigments chlorophyll a and b in chloroplasts. - The chloroplasts may be discoid, plate-like, reticulate, cup- shaped, spiral or ribbon-shaped in different species. - Most of them have one or more pyrenoids (storage bodies) located in the chloroplasts. Pyrenoids contain protein besides starch. - Some algae store food as oil droplets. - They have a rigid cell wall made of an inner layer of cellulose and an outer layer of pectose. - E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara. Reproduction: o Vegetative reproduction: By fragmentation or by formation of different types of spores. o Asexual reproduction: By flagellated zoospores produced in zoosporangia. o Sexual reproduction: Isogamous, anisogamous or oogamous.