Fungi, Viruses, Bacteria, Archaea, and Protists: Key Characteristics
Fungi: Key Characteristics
What distinguishes the fungi from other kingdoms? Fungi are eukaryotic organisms, meaning their cells have a nucleus and other organelles enclosed within membranes. Unlike plants, fungi do not perform photosynthesis. They obtain nutrients through absorption, secreting enzymes to break down complex organic matter into simpler compounds. Their cell walls contain chitin, unlike the cellulose found in plant cell walls.
What are the key physical characteristics of fungi? Fungi typically consist of a network of filaments called hyphae, which form a mass known as mycelium. They reproduce via spores, which can be produced sexually or asexually. Fungi can be unicellular (like yeasts) or multicellular (like molds and mushrooms).
Generalized Fungal Life Cycle
The fungal life cycle includes both sexual and asexual reproduction. In the asexual phase, fungi produce spores through mitosis. In the sexual phase, they undergo plasmogamy (fusion of cytoplasm), karyogamy (fusion of nuclei), and meiosis to produce genetically diverse spores.
Chytrid, Zygomycete, and Basidiomycete Life Cycles
- Chytrids: These fungi have a simple life cycle with motile spores (zoospores) that swim using flagella.
- Zygomycetes: They reproduce sexually by forming a zygosporangium, which undergoes meiosis to produce spores.
- Basidiomycetes: These fungi produce spores on basidia, typically found on the gills of mushrooms.
Ecological Importance of Fungi
Why are fungi ecologically important? Fungi play a crucial role in decomposing organic matter, recycling nutrients back into the ecosystem. They form symbiotic relationships with plants (mycorrhizae), enhancing water and nutrient absorption. Some fungi are also pathogens, affecting plants, animals, and humans.
Symbiotic Associations Between Fungi and Plants and Animals
- Mycorrhizae: Fungi form mutualistic relationships with plant roots, aiding in nutrient and water absorption.
- Lichens: Symbiotic associations between fungi and algae or cyanobacteria, where fungi provide structure and protection while the algae/cyanobacteria perform photosynthesis.
- Animal associations: Some fungi live in the guts of herbivores, helping digest cellulose.
Viruses: Characteristics and Replication
Viruses are not quite alive. Explain why. Viruses lack cellular structure and cannot carry out metabolic processes on their own. They require a host cell to replicate, making them obligate intracellular parasites.
How Viruses Replicate
- DNA viruses: Enter the host cell’s nucleus and use the host’s machinery to replicate their DNA and produce viral proteins.
- RNA viruses: Replicate in the host cell’s cytoplasm using their RNA as a template to produce viral proteins.
- RNA retroviruses: Use reverse transcriptase to convert their RNA into DNA, which integrates into the host genome and directs the production of new viruses.
Current Hypotheses on the Origin of Viruses
- Regressive hypothesis: Viruses may have evolved from small cells that parasitized larger cells.
- Cellular origin hypothesis: Viruses could have originated from pieces of DNA or RNA that escaped from the genes of a larger organism.
- Co-evolution hypothesis: Viruses might have evolved alongside their host cells.
Ecological Importance of Viruses
Why are viruses important in an ecosystem? Viruses regulate population sizes of their hosts, contribute to genetic diversity through horizontal gene transfer, and play roles in nutrient cycling by lysing cells and releasing organic matter.
Bacteria and Archaea: Prokaryotic Life
Features of Prokaryotes
Features of prokaryotes that make them important: Prokaryotes are essential for nutrient cycling, decomposing organic matter, and fixing nitrogen. They have diverse metabolic pathways, allowing them to thrive in various environments.
Structure of the Prokaryotic Cell
Prokaryotic cells lack a nucleus and membrane-bound organelles. They have a cell wall, plasma membrane, cytoplasm, ribosomes, and genetic material in a nucleoid.
Lateral/Horizontal Gene Transfer (LGT)
LGT involves the transfer of genetic material between organisms, not through traditional reproduction. It can occur via transformation, transduction, or conjugation. This process is common in bacteria, contributing to genetic diversity and rapid evolution.
Extremophiles in Archaea
Extremophiles thrive in extreme conditions. Examples include thermophiles (heat-loving), halophiles (salt-loving), and acidophiles (acid-loving).
Ecological Importance of Bacteria
Bacteria are crucial for nutrient cycling, decomposing organic matter, and forming symbiotic relationships with other organisms, such as nitrogen-fixing bacteria in plant roots.
Protists: Diverse Eukaryotes
What is a Protist?
What is a protist? Protists are a diverse group of eukaryotic microorganisms that do not fit into the other kingdoms. They can be unicellular or multicellular and have complex cellular structures.
Nutrition, Movement, and Habitat of Protists
Ways protists acquire nutrition, move, and where they live:
- Nutrition: Protists can be autotrophs (photosynthetic), heterotrophs (consume organic matter), or decomposers.
- Movement: Protists move using cilia, flagella, or pseudopodia.
- Habitat: They live in various environments, including freshwater, marine, and soil.
Examples of Protists
- Autotroph: Euglena, which uses photosynthesis.
- Heterotroph: Amoeba, which engulfs food particles.
- Decomposer: Slime molds, which break down organic matter.