Introduction to Biology: Core Principles

• 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 to maintain a stable and vital condition defined as homeostasis.

Core Principles of Biology

• Cell theory: All living organisms are composed of cells, and all cells arise from pre-existing cells.
• Gene theory: Traits are inherited through genes, which are located on chromosomes.
• Evolution: Life on Earth has evolved over time through processes like natural selection.
• Homeostasis: Living organisms maintain a stable internal environment.
• Thermodynamics: Life depends on the flow of energy, which is governed by the laws of thermodynamics.

Subdisciplines of Biology

• Biochemistry: Studies the chemical processes within and relating to living organisms.
• Molecular biology: Studies the structure and function of macromolecules essential to life, such as proteins and nucleic acids.
• Cell biology: Studies the structure, function, and behavior of cells.
• Genetics: Studies heredity and the variation of inherited characteristics.
• 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 living systems.
• Anatomy: Studies the structure of organisms and their parts.
• Microbiology: Studies microorganisms.
• Botany: Studies plants.
• Zoology: Studies animals.

Chemical Basis of Life

• Carbon is the primary element that forms the backbone of organic molecules.
• Water is essential for life and acts as a solvent in biological systems.
• Biological macromolecules are large polymers assembled from smaller repeating monomers.
• Carbohydrates: Primarily serve as energy sources and structural components.
• Lipids: Includes fats, oils, and phospholipids; involved in energy storage, cell membrane structure, and signaling.
• Proteins: Perform a wide variety of functions, including catalyzing reactions, transporting molecules, and providing structural support.
• Nucleic acids: DNA and RNA; store and transmit genetic information.

Cell Structure and Function

• Prokaryotic cells: Lack a nucleus and other membrane-bound organelles; includes bacteria and archaea.
• Eukaryotic cells: Have a nucleus and other membrane-bound organelles; includes protists, fungi, plants, and animals.
• Cell membrane: A selectively permeable barrier that controls the movement of substances into and out of the cell.
• Nucleus: Contains the cell's genetic material (DNA) and controls cell activities.
• Ribosomes: Synthesize proteins.
• Endoplasmic reticulum (ER): Involved in protein and lipid synthesis.
• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.
• Mitochondria: Generate energy (ATP) through cellular respiration.
• Chloroplasts (in plant cells): Conduct photosynthesis.
• Lysosomes: Contain enzymes for intracellular digestion.

Energy and Metabolism

• Metabolism: The sum of all chemical reactions occurring in an organism.
• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy.
• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy.
• Enzymes: Biological catalysts that speed up chemical reactions.
• ATP (adenosine triphosphate): The primary energy currency of the cell.
• Cellular respiration: The process by which cells generate ATP by breaking down organic molecules.
• Photosynthesis: The process by which plants and other organisms convert light energy into chemical energy.

Genetics

• DNA (deoxyribonucleic acid): The molecule that carries genetic information.
• Genes: Segments of DNA that encode proteins or functional RNA molecules.
• Chromosomes: Structures within the nucleus that contain DNA.
• DNA replication: The process by which DNA is copied.
• Transcription: The process by which RNA is synthesized from a DNA template.
• Translation: The process by which proteins are synthesized from an RNA template.
• Mutations: Changes in the DNA sequence that can lead to variation.
• Mendelian genetics: The principles of inheritance discovered by Gregor Mendel, including segregation and independent assortment.

Evolution

• Natural selection: The process by which organisms with traits that enhance survival and reproduction are more likely to pass on those traits to future generations.
• Adaptation: A trait that enhances an organism's survival and reproduction in a particular environment.
• Speciation: The process by which new species arise.
• Evidence for evolution: Fossil record, comparative anatomy, embryology, molecular biology, and biogeography.

Ecology

• Population: A group of individuals of the same species living in the same area.
• Community: All the populations of different species living in the same area.
• Ecosystem: A community of organisms and their physical environment.
• Biome: A large-scale community of organisms, characterized by climate and vegetation.
• Food webs: Describe the flow of energy and nutrients through an ecosystem.
• Trophic levels: The position an organism occupies in a food web (e.g., producers, consumers, decomposers).
• Biogeochemical cycles: The movement of elements (e.g., carbon, nitrogen, water) through ecosystems.

Diversity of Life

• Bacteria: Single-celled prokaryotes.
• Archaea: Single-celled prokaryotes that are distinct from bacteria.
• Eukarya: Organisms with eukaryotic cells; includes protists, fungi, plants, and animals.
• Protists: A diverse group of eukaryotic microorganisms.
• Fungi: Heterotrophic eukaryotes that obtain nutrients by absorption.
• Plants: Autotrophic eukaryotes that conduct photosynthesis.
• Animals: Heterotrophic eukaryotes that obtain nutrients by ingestion.