General Biology Study Notes: Viruses, Evolution, Prokaryotes, Eukaryotes, Plants, Fungi, and Animal Diversity

Chapter 17: Viruses and Gene Expression

Characteristics of Living Things

Living organisms share several defining characteristics that distinguish them from non-living entities.

• Cellular Organization: Composed of one or more cells.

• Genetic Information: Use and synthesize genetic information to reproduce.

• Response to Environment: React and adapt to environmental stimuli.

• Energy Utilization: Harvest energy and use it to perform functions.

• Homeostasis: Maintain stable internal conditions.

Viruses: Are They Alive?

Viruses are not considered living because they cannot reproduce or carry out metabolic processes independently; they require a host cell.

• Obligate Parasites: Must infect living cells to replicate.

• Structure: Consist of genetic material (DNA or RNA) enclosed in a protein coat (capsid).

Measles Virus Example

• Transmission: Highly contagious, airborne.

• Impact: Causes millions of deaths globally, especially among unvaccinated populations.

• Prevention: Vaccination is highly effective.

Virus Structure and Classification

Viruses exhibit diverse structural forms and can be classified based on their shape and genetic material.

• Filamentous: e.g., Tobacco mosaic virus.

• Icosahedral: e.g., Adenovirus.

• Enveloped: e.g., Influenza virus.

• Bacteriophage: Complex head and tail structure, infects bacteria.

Viral Replication Cycles

Viruses replicate by attaching to host cells and injecting their genetic material, which is then used to produce new viral particles.

• Lytic Cycle: Virus replicates rapidly, lyses host cell.

• Lysogenic Cycle: Viral DNA integrates into host genome, replicates with host cell until triggered to enter lytic cycle.

HIV and Retroviruses

• Retrovirus: Contains RNA, uses reverse transcriptase to synthesize DNA.

• HIV: Infects T-helper cells, causes AIDS.

• CCR5 Mutation: Some individuals have a mutation that confers resistance to HIV infection.

Prions

• Definition: Infectious proteins that cause neurodegenerative diseases.

• Example: Mad cow disease.

Chapter 24: Evolution and the History of Life

Themes of Evolution on Earth

Evolution explains the diversity of life through descent from common ancestors and adaptation to environments.

• Adaptation: Inherited traits that enhance fitness in specific environments.

• Natural Selection: Mechanism driving evolution by favoring advantageous traits.

Conditions of Primitive Earth

• Earth is ~4.5 billion years old.

• Primitive atmosphere contained CO2, N2, CH4, NH3, H2, and H2O.

• Formation of organic molecules was possible under these conditions.

Origin of Life Experiments

• Urey-Miller Experiment: Simulated early Earth conditions, produced amino acids and organic molecules.

• Abiotic Synthesis: Formation of polymers and membranes in laboratory settings.

RNA World Hypothesis

• Suggests that self-replicating RNA molecules were precursors to cellular life.

• RNA can act as both genetic material and catalyst (ribozyme).

Chapter 27: Bacteria and Archaea

Prokaryotic Diversity

Prokaryotes include Bacteria and Archaea, which are distinguished by their genetic, biochemical, and ecological characteristics.

• Bacteria: Ubiquitous, diverse metabolic pathways.

• Archaea: Often found in extreme environments (high temperature, salinity, pH).

Prokaryotic Cell Structure

• No nucleus: DNA in nucleoid region.

• No membrane-bound organelles.

• Cell wall: Peptidoglycan in bacteria, pseudopeptidoglycan in archaea.

Genetic Variation in Prokaryotes

• Rapid Reproduction: Binary fission.

• Horizontal Gene Transfer: Transformation, transduction, conjugation.

Prokaryotes and Humans

• Pathogenic bacteria: Cause diseases.

• Beneficial bacteria: Aid in digestion, nutrient cycling.

Chapter 25: The History of Life on Earth

Prokaryotes vs. Eukaryotes

• Prokaryotes: No nucleus, simple cell structure.

• Eukaryotes: Nucleus, membrane-bound organelles, complex structure.

Endosymbiont Theory

This theory proposes that mitochondria and chloroplasts originated from free-living bacteria engulfed by ancestral eukaryotic cells.

• Evidence: Double membranes, circular DNA, binary fission, ribosomes similar to bacteria.

Multicellularity in Eukaryotes

• Requires cell adhesion, communication, and differentiation.

• True multicellularity evolved independently in plants, animals, and fungi.

Chapter 29 & 30: Plant Diversity and Evolution

Adaptations for Life on Land

• Cuticle: Waxy layer prevents water loss.

• Stomata: Pores for gas exchange.

• Vascular tissue: Xylem and phloem transport water and nutrients.

Seed Evolution

• Seeds: Multicellular, protective coat, food supply for embryo.

• Gymnosperms: Naked seeds, e.g., pine trees.

• Angiosperms: Flowering plants, seeds enclosed in fruit.

Chapter 31: Fungi

Fungal Structure and Function

• Hyphae: Filamentous structures for absorption.

• Mycelium: Network of hyphae.

• Cell wall: Made of chitin.

Fungal Reproduction

• Sexual and asexual cycles: Involve spore formation and fusion of nuclei.

Chapter 32-34: Animal Diversity and Evolution

General Characteristics of Animals

• Multicellular, heterotrophic, motile.

• Specialized tissues: Muscle, nervous tissue.

• Reproduction: Mostly sexual, with diploid life cycle.

Major Animal Phyla

• Porifera: Sponges, no true tissues.

• Cnidaria: Jellies, corals, radial symmetry.

• Bilateria: Bilateral symmetry, includes most animal phyla.

• Chordata: Vertebrates, notochord, dorsal nerve cord.

Evolutionary Trends

• Symmetry: Radial vs. bilateral.

• Cephalization: Development of a head region.

• Segmentation: Repeated body units.

Human Evolution

• Hominins: Diverged from chimpanzees 5-7 mya.

• Key traits: Bipedalism, large brain, tool use, symbolic thought.

HTML Table: Comparison of Prokaryotes and Eukaryotes

Feature	Prokaryotes	Eukaryotes
Nucleus	No	Yes
Organelles	No	Yes
Cell Wall	Peptidoglycan (Bacteria)	Cellulose (Plants), Chitin (Fungi)
Genetic Material	Circular DNA	Linear DNA
Reproduction	Binary Fission	Mitosis/Meiosis

Key Equations and Concepts

• Hardy-Weinberg Equation: $p^2 + 2pq + q^2 = 1$

• Photosynthesis: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

• Cellular Respiration: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

Additional info: Some explanations and examples have been expanded for clarity and completeness.