Unit 3: Fungi Diversity

General Characteristics of Fungi

Fungi are a diverse group of eukaryotic organisms that share several features with plants but are more closely related to animals. They play crucial roles in ecosystems as decomposers, symbionts, and pathogens.

• Heterotrophic Nutrition: Fungi obtain nutrients by absorbing them from their environment, often by secreting enzymes to break down complex materials.

• Cell Structure: Fungi have chitin in their cell walls, are mostly multicellular (except yeasts), and possess nuclei and mitochondria.

• Growth Forms: Fungi can be haploid (N), diploid (2N), or dikaryotic (N+N).

Major Fungal Groups and Their Characteristics

• Chytridiomycota: Primarily aquatic, with flagellated spores. Example: Batrachochytrium dendrobatidis (contributes to amphibian decline).

• Glomeromycota: Form arbuscular mycorrhizae with plants, aiding nutrient uptake. Most species are mutualistic.

• Zygomycota: ~1000 species, mostly saprotrophic. Life cycle includes zygosporangium and sexual/asexual reproduction.

• Ascomycota: ~65,000 species, includes yeasts, molds, and morels. Sexual spores (ascospores) produced in asci.

• Basidiomycota: ~30,000 species, includes mushrooms, puffballs, and shelf fungi. Sexual spores (basidiospores) produced on basidia.

Ecological Roles of Fungi

• Decomposers: Break down dead organic matter, recycling nutrients.

• Symbionts: Form mutualistic relationships (e.g., mycorrhizae with plants, lichens with algae/cyanobacteria).

• Pathogens: Cause diseases in plants and animals (e.g., rusts, smuts, Dutch elm disease).

Unit 2: Plant Diversity

General Characteristics of Plants

Plants are multicellular, photosynthetic eukaryotes that play a foundational role in terrestrial ecosystems. They exhibit a wide range of adaptations for life on land.

• Photosynthesis: Plants use sunlight to convert CO2 and water into glucose and oxygen.

• Cell Structure: Plant cells have cell walls (cellulose), chloroplasts, and large central vacuoles.

• Life Cycle: Alternation of generations between multicellular haploid (gametophyte) and diploid (sporophyte) stages.

Adaptations for Terrestrial Life

• Cuticle and Stomata: Prevent water loss and allow gas exchange.

• Vascular Tissue: Xylem and phloem transport water, minerals, and nutrients.

• Seeds and Pollen: Enable reproduction without water, protect embryos, and facilitate dispersal.

Major Plant Groups

• Nonvascular Plants: Mosses, liverworts, hornworts. Lack vascular tissue; gametophyte is dominant.

• Seedless Vascular Plants: Ferns, lycophytes, horsetails. Sporophyte is dominant; reproduce via spores.

• Gymnosperms: Seed plants with naked seeds (no fruit). Includes conifers, cycads, ginkgo.

• Angiosperms: Flowering plants with seeds enclosed in fruit. Exhibit double fertilization and diverse flower structures.

Reproductive Strategies

• Homosporous vs. Heterosporous: Homosporous plants produce one type of spore; heterosporous plants produce microspores (male) and megaspores (female).

• Pollination: Transfer of pollen from anther to stigma; can be biotic (animals) or abiotic (wind).

• Double Fertilization (Angiosperms): One sperm fertilizes the egg, another fuses with two nuclei to form endosperm.

Plant Structure and Function

• Monocots vs. Dicots: Monocots have one cotyledon, parallel veins, and flower parts in multiples of three. Dicots have two cotyledons, net-like veins, and flower parts in multiples of four or five.

• Vascular Plant Organs: Roots, stems, leaves; specialized for support, transport, and photosynthesis.

Ecological Importance of Plants

• Ecosystem Services: Plants provide oxygen, food, habitat, and regulate climate.

• Resource Provision: Source of medicines, materials, and aesthetic value.

Unit 4: Viruses

General Characteristics of Viruses

Viruses are acellular infectious agents composed of genetic material (DNA or RNA) enclosed in a protein coat (capsid), sometimes with a lipid envelope. They require host cells to replicate and do not carry out metabolic processes independently.

• Structure: Genome (DNA or RNA), capsid, and sometimes an envelope.

• Size: Very small, much smaller than cells.

• Replication: Use host cell machinery to reproduce.

Virus Classification and Evolution

• Baltimore Classification: Based on genome type and replication method (e.g., dsDNA, ssRNA).

• Evolutionary Theories: Viruses may have evolved from escaped genetic material, degenerated cells, or pre-cellular life forms.

Virus Life Cycle

• Attachment and Entry: Virus binds to host cell and injects genetic material.

• Replication: Host cell replicates viral genome and produces viral proteins.

• Assembly and Release: New viruses are assembled and released, often destroying the host cell.

RNA vs. DNA Viruses

• RNA Viruses: Often mutate rapidly, can cause diseases like influenza and COVID-19.

• DNA Viruses: More stable genomes, examples include chickenpox and herpes.

Transmission and Disease

• Transmission: Can occur via air, bodily fluids, or vectors. Virulence depends on transmission mode and host susceptibility.

• Examples of Diseases: Polio, smallpox, HIV/AIDS, influenza.

• Zoonotic Viruses: Viruses that cross from animals to humans (e.g., Ebola, SARS).

Immunity and Vaccination

• Vaccines: Use weakened or killed viruses to stimulate immune response. mRNA vaccines use genetic material to produce viral proteins in host cells.

• Herd Immunity: Occurs when a large portion of the population is immune, reducing disease spread.

• Scientific Consensus: No evidence that vaccines cause autism.

Table: Comparison of Fungi, Plants, and Viruses

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard General Biology curriculum.