Diversity of Life: Viruses, Prokaryotes, Eukaryotes, Plants, Fungi, and Animals (Ch. 17, 24–27) – Study Guide

Diversity of Life Unit: Viruses, Prokaryotes, Eukaryotes, Plants, Fungi, and Animals

Overview

This study guide covers key concepts from Chapters 17, 24, 25, 26, and 27, focusing on the diversity of life, including viruses, prokaryotes, eukaryotes, plants, fungi, and animals. The notes are organized by major topics and subtopics, with definitions, explanations, and examples to support exam preparation.

Viruses (Chapter 17)

Structure and Classification of Viruses

• Viral Genomes: Can be double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA.

• Capsid: Protein shell that encloses the viral genome; shapes include helical, icosahedral, or more complex forms.

• Envelope: Some animal viruses have a membrane envelope derived from the host cell membrane, which helps the virus infect host cells.

Viral Infection and Replication

• Attachment: Determined by specific viral proteins that bind to host cell receptors ("lock-and-key" fit).

• Obligate Intracellular Parasites: Viruses require a host cell to replicate; they cannot reproduce independently.

• Host Range: The spectrum of host cells a virus can infect; determined by viral surface proteins and host cell receptors.

• Use of Host Machinery: Viruses use host enzymes, ribosomes, tRNAs, amino acids, ATP, and other components to replicate.

Viral Life Cycles

• Lytic Cycle: Virus replicates and lyses the host cell, releasing new virions.

• Lysogenic Cycle: Viral DNA integrates into the host genome and replicates with it, remaining dormant until triggered.

• Retroviruses: RNA viruses that use reverse transcriptase to synthesize DNA from their RNA genome (e.g., HIV).

Medical and Evolutionary Aspects

• Vaccines: Harmless derivatives of pathogens that stimulate the immune system to mount defenses.

• Prions: Infectious proteins causing neurodegenerative diseases (e.g., mad cow disease); they are difficult to destroy and can be transmitted by ingestion.

• Emerging Viruses: New or previously rare viruses that can cause outbreaks due to mutation, host range expansion, or spread from isolated populations.

• Eradicated Disease: Smallpox is the only viral disease eradicated by vaccination.

Why Viruses Are Not Considered Alive

• They cannot replicate or carry out metabolic processes outside a host cell.

• They lack cellular structure and do not possess all characteristics of living organisms.

Origin of Life and Prokaryotic Diversity (Chapter 24)

Origin of Life: Key Experiments and Hypotheses

• Miller-Urey Experiment: Demonstrated that organic molecules could form under prebiotic Earth conditions, supporting the hypothesis that life arose from chemical evolution.

• Sequence of Events: Abiotic synthesis of small molecules → joining into macromolecules → packaging into protocells → origin of self-replicating molecules (RNA world hypothesis).

Prokaryotic Cell Structure and Diversity

• Domains: Bacteria and Archaea.

• Shapes: Cocci (spherical), bacilli (rod-shaped), spirilla (spiral).

• Cell Wall: Gram-positive (thick peptidoglycan) vs. Gram-negative (thin peptidoglycan, outer membrane with lipopolysaccharides).

• Genetic Diversity: Horizontal gene transfer (conjugation, transformation, transduction) increases genetic variation.

Prokaryotic Roles and Evolution

• Ecological Importance: Prokaryotes are essential for nutrient cycling, decomposition, and as primary producers.

• Cyanobacteria: First to evolve oxygenic photosynthesis, leading to the Oxygen Revolution and the rise of aerobic life.

• Archaea: Include extremophiles (halophiles, thermophiles, methanogens).

Origin and Diversification of Eukaryotes (Chapter 25)

Endosymbiotic Theory

• Mitochondria and Chloroplasts: Originated from engulfed prokaryotes; evidence includes double membranes, their own DNA, and similarities to bacteria.

• Primary vs. Secondary Endosymbiosis: Primary involves direct engulfment of a prokaryote; secondary involves engulfment of a eukaryotic cell that already contains an endosymbiont.

Protist Diversity

• Supergroups: SAR, Archaeplastida, Excavata, Unikonta.

• Polyphyletic Group: Protists are not a single clade; they include all eukaryotes that are not plants, animals, or fungi.

Colonization of Land: Plants and Fungi (Chapter 26)

Plant Evolution and Adaptations

• Key Innovations: Embryos, vascular tissue, seeds, flowers.

• Alternation of Generations: Plants alternate between multicellular haploid (gametophyte) and diploid (sporophyte) stages.

• Vascular Tissue: Xylem (water transport), phloem (sugar and nutrient transport).

• Seeds: Protect and nourish the embryo, aid in dispersal.

• Cuticle and Stomata: Adaptations to prevent water loss and allow gas exchange.

Fungi and Symbiosis

• Structure: Composed of hyphae (filaments) forming a mycelium (mass).

• Nutrition: Heterotrophic by absorption; secrete enzymes to break down organic matter.

• Mycorrhizae: Symbiotic associations with plant roots, enhancing nutrient uptake.

• Lichens: Symbiotic associations between fungi and photosynthetic organisms (algae or cyanobacteria).

Rise of Animal Diversity (Chapter 27)

Animal Characteristics and Evolution

• Unique Cell Types: Muscle and nervous cells are unique to animals.

• Major Phyla: Arthropods (insects, spiders, crustaceans), Mollusks, Chordates (vertebrates).

• Body Symmetry: Radial (e.g., jellyfish) vs. bilateral (e.g., humans, dogs).

• Evolutionary Innovations: Amniotic egg, segmentation, cephalization.

• Vertebrates: Animals with backbones; mammals are characterized by mammary glands and hair.

Human Evolution

• Out of Africa Hypothesis: Modern humans originated in Africa and migrated outward, supported by genetic evidence.

• Key Traits: Upright posture, large brain, tool use, language.

• Evolutionary Trees: Show relationships among hominins and the timing of divergence events.

Tables

Examples of Table Content

Topic	Key Points
Viral Genomes	Double-stranded DNA, single-stranded DNA, double-stranded RNA, single-stranded RNA
Prokaryotic Shapes	Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral)
Plant Vascular Tissue	Xylem (water), Phloem (sugars, nutrients)
Animal Symmetry	Radial (jellyfish), Bilateral (humans, dogs)

Additional info: Some explanations and context have been expanded for clarity and completeness, including definitions, evolutionary context, and examples not explicitly stated in the original notes.