Exploring the Diversity of Life: Viruses, Bacteria, Protists, Fungi, and Plants
1. Viruses
Characteristics of Life:
Viruses do not meet all criteria for life since they are acellular and cannot reproduce independently. They require a host cell to replicate, using its machinery for survival (Unit2_Slides).
Virus Structure:
Nonenveloped viruses consist only of a capsid (protein shell) and genetic material.
Enveloped viruses have both a capsid and an outer membrane-like envelope, which makes them more vulnerable outside a host (Unit2_Slides).
Genetic Material:
Viruses have either DNA (stable, less prone to mutation) or RNA (more mutation-prone, lacks proofreading), impacting mutation rates. RNA viruses tend to evolve faster due to these high mutation rates (Unit2_Slides).
Prevention:
Vaccines expose the immune system to pieces or inactivated forms of the virus, helping the body recognize and defend against it without causing illness. Few antiviral drugs exist because viruses use host cells, making it hard to target them without harming the host (Unit2_Slides).
Written Question Example:
Explain why RNA viruses tend to mutate faster than DNA viruses.
2. Bacteria
Bacteria vs. Archaea:
Bacteria and archaea are prokaryotic, but archaea have unique side chains in their plasma membranes and lack the peptidoglycan found in bacterial cell walls (Unit2_Slides).
Gram-Positive and Gram-Negative Bacteria:
Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, staining purple in tests.
Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane, staining pink and often more resistant to antibiotics (Unit2_Slides).
Evolution and Antibiotic Resistance:
Due to their quick generation times and high mutation rates, bacteria evolve rapidly, sometimes leading to antibiotic resistance, a critical global health issue (Unit2_Slides).
Written Question Example:
Describe the differences between gram-positive and gram-negative bacteria and their implications for antibiotic resistance.
3. Protists
Protist Groupings:
- Protozoa: Animal-like, heterotrophic, and often move using structures like cilia or pseudopodia.
- Algae: Plant-like, photosynthetic, include groups like dinoflagellates (bioluminescent and can cause red tides) and diatoms (have silica shells and play a role in carbon cycling) (Unit2_Slides).
Endosymbiosis Theory:
Suggests that eukaryotic organelles (mitochondria and chloroplasts) originated from prokaryotic cells engulfed by a host cell, supported by evidence like double membranes and independent replication through fission (Unit2_Slides).
Written Question Example:
Summarize the endosymbiosis theory and provide at least two pieces of evidence supporting it.
4. Fungi
Structure and Reproduction:
Hyphae are long, thin filaments increasing surface area for nutrient absorption.
Fungi reproduce through various structures, including:
- Zygospores (Phylum Zygomycota) in black bread mold.
- Asci (Phylum Ascomycota) in sac fungi like truffles.
- Basidia (Phylum Basidiomycota) in mushrooms (Unit2_Slides).
Symbiotic Relationships:
- Lichens: A symbiosis between fungi and algae/cyanobacteria, where fungi provide protection and algae/cyanobacteria contribute food.
- Mycorrhizal fungi: Form partnerships with plant roots, aiding in mineral absorption, critical for plant nutrition (Unit2_Slides).
Written Question Example:
Explain the mutualistic relationship between mycorrhizal fungi and plants, including the benefits for each partner.
5. Plant Kingdom (Seedless and Seeded Plants)
Colonization Challenges:
Plants developed vascular tissue to transport water and nutrients (xylem and phloem) and seeds for protecting embryos and surviving dry conditions (Unit2_Slides).
Seedless Plants:
- Nonvascular (Bryophytes): Small and need water for reproduction, e.g., mosses. Their life cycle is dominated by the gametophyte stage.
- Vascular (Pteridophytes): Have vascular tissues and reproduce using spores, e.g., ferns. Their life cycle is dominated by the sporophyte stage (Unit2_Slides).
Seed Plants:
- Gymnosperms: Have “naked” seeds and include conifers like pine trees. They rely on wind for pollen dispersal.
- Angiosperms: Flowering plants with seeds enclosed in fruits, which aid in seed dispersal by attracting animals. Flowers contain reproductive structures that enable complex pollination strategies (Unit2_Slides).
Coevolution of Plants and Pollinators:
Angiosperms evolved with pollinators like insects and birds, leading to diverse flower forms and specialized pollination. For instance, bright-colored flowers attract bees, which assist in pollen transfer (Unit2_Slides).
Written Question Example:
Describe how vascular tissue and seeds contributed to the adaptation of plants to land environments.