Introduction to Biology

• Biology is the scientific study of life.
• It explores the structure, function, growth, origin, evolution, and distribution of living organisms.
• Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation and extinction of species.
• Living organisms are open systems that survive by transforming energy and decreasing their local entropy.

Core Principles of Biology

• Cell theory: All living organisms are composed of cells.
• Gene theory: Hereditary information is encoded in DNA and genes.
• Evolution: Life evolves over time through natural selection.
• Homeostasis: Living organisms maintain a stable internal environment.
• Thermodynamics: Life operates according to the laws of thermodynamics, involving energy transfer and transformation.

Branches of Biology

• Biochemistry: Studies the chemical processes within and relating to living organisms.
• Molecular Biology: Examines the molecular basis of biological activity between biomolecules in the various systems of a cell.
• Cell Biology: Studies the structure, function, and behavior of cells.
• Genetics: Studies heredity and variation of organisms.
• Evolutionary Biology: Studies the evolutionary processes that produced the diversity of life on Earth.
• Ecology: Studies the interactions of organisms with each other and their environment.
• Physiology: Studies the functions and mechanisms in a living system.
• Anatomy: Studies the structure of organisms and their parts.
• Microbiology: Studies microorganisms, including bacteria, viruses, and fungi.
• Botany: Studies plants, including their physiology, structure, genetics, and ecology.
• Zoology: Studies animals, including their behavior, physiology, structure, and evolution.

Cell Structure and Function

• Cells are the basic units of life, responsible for all life processes.
• Two main types: eukaryotic and prokaryotic.
• Eukaryotic cells: Have a nucleus and other membrane-bound organelles; found in plants, animals, fungi, and protists.
• Prokaryotic cells: Lack a nucleus and other membrane-bound organelles; found in bacteria and archaea.
• Key organelles in eukaryotic cells include: nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and ribosomes.
• The plasma membrane surrounds the cell and regulates the movement of substances in and out.
• Cell functions include: metabolism, growth, reproduction, and response to stimuli.

Genetics and Heredity

• Genes are the units of heredity, composed of DNA.
• DNA (deoxyribonucleic acid): Carries the genetic instructions for all living organisms.
• Genes are organized into chromosomes.
• Human cells contain 23 pairs of chromosomes.
• DNA replication: Process by which DNA makes copies of itself.
• Transcription: Process by which the information in DNA is copied into RNA.
• Translation: Process by which RNA is used to synthesize proteins.
• Mutations: Changes in the DNA sequence that can lead to variations in traits.
• Mendelian genetics: Principles of inheritance based on the work of Gregor Mendel, including segregation and independent assortment.

Evolution

• Evolution: Change in the heritable characteristics of biological populations over successive generations.
• Natural selection: Mechanism of evolution where organisms with advantageous traits are more likely to survive and reproduce.
• Evidence for evolution: Fossil record, comparative anatomy, embryology, biogeography, and molecular biology.
• Adaptation: Traits that enhance an organism's survival and reproduction in its environment.
• Speciation: Process by which new species arise.
• Phylogeny: Evolutionary history and relationships of organisms.

Ecology and Ecosystems

• Ecology: Study of the interactions between organisms and their environment.
• Ecosystem: Community of living organisms (biotic factors) interacting with their physical environment (abiotic factors).
• Trophic levels: Position an organism occupies in a food chain (e.g., producers, consumers, decomposers).
• Food web: Interconnected network of food chains in an ecosystem.
• Energy flow: Passage of energy through the trophic levels of an ecosystem.
• Nutrient cycling: Movement of nutrients (e.g., carbon, nitrogen, phosphorus) through an ecosystem.
• Biomes: Large geographic areas characterized by specific climate conditions, animal populations, and plant communities.
• Population ecology: Studies the dynamics of populations and how they interact with their environment.
• Community ecology: Studies the interactions between different species within a community.

Biological Processes

• Photosynthesis: Process by which plants and other organisms convert light energy into chemical energy in the form of glucose.
• Cellular respiration: Process by which cells break down glucose to release energy in the form of ATP.
• Metabolism: Sum of all chemical reactions that occur within a living organism.
• Homeostasis: Maintenance of a stable internal environment in the face of changing external conditions.
• Reproduction: Process by which organisms produce offspring, either sexually or asexually.
• Development: Process by which an organism grows and matures.
• Response to stimuli: Ability of organisms to detect and respond to changes in their environment.

Classification of Living Organisms

• Taxonomy: Science of classifying and naming organisms.
• Linnaean system: Hierarchical system of classification developed by Carl Linnaeus.
• Taxonomic ranks: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
• Three domains of life: Bacteria, Archaea, and Eukarya.
• Six kingdoms of life: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia.
• Binomial nomenclature: System of naming species using two names: the genus and the species epithet (e.g., Homo sapiens).

Viruses

• Viruses: Non-cellular entities that consist of nucleic acid (DNA or RNA) enclosed in a protein coat.
• Viruses require a host cell to replicate.
• Viral replication: Virus attaches to a host cell, injects its genetic material, uses the host cell's machinery to produce more virus particles, and then releases the new viruses to infect other cells.
• Viruses can cause a wide range of diseases in plants and animals.