General Biology: Foundations, Genetics, and Evolution Study Notes

Biology: Characteristics of Life

Defining Life

Biology is the study of life, which must meet specific criteria to be considered living. Organisms must possess all characteristics of life, including reproduction, growth, development, energy use, cellular organization, and evolution.

• Characteristics of Life: Reproduction, growth, development, energy use, cells, order, evolution

• Energy Use: Life requires energy, which is brought in, converted, and expelled. Heat is lost every time energy is transferred.

Cellular Organization

• Unicellular: Living organisms with one cell

• Multicellular: Living organisms with trillions of cells

Order and Homeostasis

• Life is organized: organism → organ system → organ → tissue → cell → organelle → molecule → atom

• Homeostasis: The process by which a cell or organism maintains equilibrium (e.g., internal thermostat regulates temperature).

Evolution

Evolution is the process of biological change in which species accumulate differences from their ancestors as they adapt to different environments over time. It explains both the diversity and unity of organisms.

• Scientific explanation: Diversity and unity of organisms

Scientific Method and Reasoning

Science as a Process

Science is dynamic and involves constructing and testing hypotheses to explain observations.

• Testable: Hypotheses must be testable by experiments or observations.

• Repeatable: Observations must be independently verified.

• Falsifiable: Hypotheses can be disproven.

Types of Reasoning

• Inductive Reasoning: Drawing general conclusions from specific observations.

• Deductive Reasoning: Drawing specific conclusions from general principles.

Empirical Facts and Hypotheses

• Empirical Fact: An observation or statement about the natural world, confirmed by experimentation and observation.

• Hypothesis: A tentative explanation that can be tested and potentially falsified.

Evolution: Fact and Theory

Paleontology and Uniformitarianism

• Paleontology: Study of fossils, developed by Georges Cuvier.

• Uniformitarianism: Proposed by James Hutton, stating geological features evolve gradually.

Transmutation and Species Change

• Transmutation: Species change over time by common descent.

• Jean-Baptiste Lamarck: Proposed inheritance of acquired characteristics.

• Charles Darwin: Proposed natural selection as a mechanism for evolution.

Genetics: Chromosomes, Genes, and Inheritance

Chromosomes and Genes

Genetics is the study of heredity and variation in organisms. Chromosomes are structures composed of DNA and proteins, carrying genetic information.

• Chromosome: Strand of DNA with thousands of genes

• Gene: Unit of inheritance, a segment of DNA that codes for a protein

• Locus: Position of a gene on a chromosome

Chromosome Theory of Inheritance

Chromosomes are carriers of genetic material. Humans have 46 chromosomes (23 pairs).

Cell Type	Chromosome Number
Gametes (egg/sperm)	23 chromosomes (haploid)
Somatic cells	46 chromosomes (diploid)

Barriers to Reproduction

• Prezygotic Barriers: Prevent fertilization (e.g., behavioral, temporal, mechanical isolation)

• Postzygotic Barriers: Affect viability or fertility of hybrid offspring (e.g., reduced hybrid fertility/viability)

DNA: Structure and Function

DNA as Genetic Material

DNA is the molecule that carries genetic information. Experiments by Hershey and Chase demonstrated that DNA, not protein, is the genetic material.

• DNA Structure: Double helix, antiparallel strands, composed of nucleotides (A, T, C, G)

• Chargaff's Rules: %A = %T, %C = %G

Gene Expression

Gene expression is the process by which DNA directs the synthesis of proteins, leading to specific traits.

• Phenotype: Observable trait

• Genotype: Genetic code for the phenotype

Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information:

• Transcription: DNA → RNA

• Translation: RNA → Protein

RNA

• RNA: Ribonucleic acid, single-stranded, contains uracil (U) instead of thymine (T)

Genetic Code and Mutation

Codons

Codons are sequences of three nucleotides in mRNA that code for specific amino acids.

• Multiple codons can code for the same amino acid (redundancy)

Mutation

Mutations are changes in the genetic code that can affect protein function and lead to genetic diseases.

• Point Mutations: Affect a single nucleotide

• Sickle Cell Disease: Caused by a point mutation in the hemoglobin gene

Type of Point Mutation	Description
Substitution	One nucleotide is replaced by another
Insertion/Deletion	Nucleotides are added or removed, possibly causing frameshift
Missense Mutation	Changes amino acid sequence
Nonsense Mutation	Creates a stop codon, truncating the protein

Microevolution and Macroevolution

• Microevolution: Evolution within a species (small scale)

• Macroevolution: Evolution above the species level (large scale)

Systematics and Phylogeny

Classification of Life

Systematics is the study of biological classification and relationships among organisms. Phylogeny is the evolutionary history of a species.

• Taxonomy: Naming and classifying organisms

• Phylogenetic Tree: Diagram showing evolutionary relationships

Prokaryotes and Eukaryotes

Cell Types

• Prokaryotes: No nucleus, include Bacteria and Archaea

• Eukaryotes: Have a nucleus, include plants, animals, fungi, and protists

Bacteria and Archaea

• Bacteria: Can be pathogens, have peptidoglycan cell walls, may be antibiotic-resistant

• Archaea: Distinct from bacteria, often found in extreme environments

Additional info: Some context and examples were inferred to clarify fragmented points and ensure completeness.