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Semester 1: PLANT DIVERSITY I
Algae: Introduction, history, classification, reproduction, life cycle, phylogeny, and evolutionary trends
Algae
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Algae are simple, photosynthetic organisms found in various aquatic environments. They play a crucial role in ecosystems by producing oxygen and serving as a primary food source.
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The history of algae dates back over a billion years, with fossil evidence suggesting that they were among the first photosynthetic organisms on Earth. They have been significant in the evolution of life by contributing to atmospheric oxygen.
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Algae are classified into several groups based on their pigmentation, cell structure, and habitat. Major groups include green algae (Chlorophyta), brown algae (Phaeophyceae), red algae (Rhodophyta), and blue-green algae (Cyanobacteria).
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Reproduction in algae can be sexual or asexual. Asexual reproduction occurs through fragmentation, budding, or spore formation. Sexual reproduction involves gamete formation and fertilization, leading to the creation of zygotes.
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The life cycle of algae includes alternation of generations, consisting of a haploid gametophyte phase and a diploid sporophyte phase. The specific cycle varies among different algal groups.
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The phylogeny of algae reveals their evolutionary relationships and lineage. Molecular studies have led to a better understanding of the evolutionary history of various algal groups.
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Evolutionary trends in algae display adaptations to diverse habitats, increased complexity in structure, and variations in reproduction strategies. These adaptations have allowed algae to thrive in both freshwater and marine environments.
Fungi: General characteristics, classification, reproduction, and phylogeny
Fungi: General characteristics, classification, reproduction, and phylogeny
General Characteristics
Fungi are eukaryotic organisms characterized by their cell walls made of chitin, multicellular or unicellular forms, heterotrophic mode of nutrition, and their ability to reproduce sexually and asexually. They play crucial roles in ecosystems as decomposers, symbionts, and pathogens.
Classification
Fungi are classified into several groups, primarily: Chytridiomycota (chytrids), Zygomycota (bread molds), Ascomycota (sac fungi), Basidiomycota (club fungi), and Glomeromycota (arbuscular mycorrhizal fungi). Each group exhibits unique reproductive structures and life cycles.
Reproduction
Fungi reproduce through a variety of methods, including asexual reproduction via spores produced in structures like sporangia or conidia, and sexual reproduction which involves the fusion of hyphae and the formation of specialized reproductive structures. The sexual cycle is often more complex and involves processes such as plasmogamy, karyogamy, and meiosis.
Phylogeny
The phylogeny of fungi is highlighted by their evolutionary relationships, which can be analyzed through molecular techniques, particularly DNA and RNA sequencing. Fungi are more closely related to animals than to plants, as revealed by molecular phylogenetics, indicating a common ancestor that diverged from a single-celled eukaryote.
Lichens: Classification, structure, reproduction
Lichens: Classification, Structure, Reproduction
Classification
Lichens are classified into various groups based on their morphology and the type of fungi and photosynthetic partners they have. The main classifications are: 1. Crustose - flat and tightly adhered to the substrate. 2. Foliose - leaf-like structures with distinct upper and lower surfaces. 3. Fruticose - bushy or branched structure, often hanging or erect.
Structure
Lichens consist of three main layers: 1. Cortex - outer protective layer. 2. Medulla - inner layer that contains loosely packed fungal hyphae and sometimes algal cells. 3. Algal Layer - contains the photosynthetic partner, usually green algae or cyanobacteria, which provide nutrients through photosynthesis.
Reproduction
Lichens can reproduce both sexually and asexually. 1. Asexual reproduction - occurs through fragmentation or the production of soredia (small clusters of algal cells and fungi). 2. Sexual reproduction - involves the formation of ascospores within the fruiting bodies of the fungal partner.
Bryophytes: General characters, classification, distribution, reproduction, and economic importance
Bryophytes
Bryophytes are non-vascular land plants that include mosses, liverworts, and hornworts. They are characterized by their gametophyte-dominant life cycle, lack of true roots, stems, and leaves, and their ability to thrive in moist environments. They reproduce through spores and require water for fertilization.
Bryophytes are classified into three main groups: Mosses (Phylum Bryophyta), Liverworts (Phylum Marchantiophyta), and Hornworts (Phylum Anthocerotophyta). Each group displays unique morphological and ecological traits.
Bryophytes are widely distributed across the globe, primarily found in damp and shaded environments such as forests, wetlands, and riverbanks. They are adaptable and can survive in extremes from deserts to polar regions.
Bryophytes reproduce sexually and asexually. Sexual reproduction involves the formation of gametes in structures called gametangia. Asexual reproduction occurs through fragmentation, gemmae, or spores. Water is essential for the fertilization process in sexual reproduction.
Bryophytes play a significant role in ecosystems as soil stabilizers and contributors to water retention. They are also used in horticulture, traditional medicine, and as indicators of environmental health. Certain mosses are harvested for decorative purposes and soil additives.
