Introduction to Biology

Biology is the scientific study of life, exploring structure, function, growth, origin, evolution, and distribution of living organisms.

Core Principles

• Cell theory states all living organisms are composed of cells.
• Gene theory states hereditary information is encoded in DNA and passed from parents to offspring.
• Evolution describes life evolving over time through natural selection and other processes.
• Homeostasis enables living organisms to maintain a stable internal environment.

Levels of Biological Organization

• Molecules: Atoms combine to form molecules like DNA and proteins.
• Cells: The basic unit of life, consisting of organelles, enclosed by a membrane.
• Tissues: Groups of similar cells performing specific functions.
• Organs: Structures composed of different tissues working together.
• Organ systems: Groups of organs cooperating to perform major bodily functions.
• Organisms: Individual living beings.
• Populations: Groups of individuals of the same species living in the same area.
• Communities: Populations of different species interacting with each other.
• Ecosystems: Communities interacting with their physical environment.
• Biosphere: The sum of all ecosystems on Earth.

Key Concepts

• Genetics: Study of heredity and genes.
• Evolution: Change in heritable characteristics of biological populations over generations.
• Ecology: Study of interactions between organisms and their environment.
• Physiology: Study of functions and mechanisms in a living system.
• Anatomy: Study of the structure of living things.

Chemical Basis of Life

• Matter consists of chemical elements in pure form and in combinations called compounds.
• Elements cannot be broken down into other substances by chemical reactions.
• Essential elements for life: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHNOPS).
• Atoms combine to form molecules through chemical bonds.
• Covalent, ionic, and hydrogen bonds are important in biological molecules.
• Water is essential for life due to cohesion, adhesion, high specific heat, evaporative cooling, and versatility as a solvent.

Biological Macromolecules

• Large molecules necessary for life, including carbohydrates, lipids, proteins, and nucleic acids.
• Polymers are large molecules made by stringing together smaller building blocks called monomers.
• Carbohydrates:
  • Include sugars and polymers of sugars.
  • Primary source of energy.
  • Serve as structural components of cells and tissues.
  • Monosaccharides (glucose, fructose) are simple sugars.
  • Polysaccharides (starch, glycogen, cellulose) are complex carbohydrates.
• Lipids:
  • Include fats, phospholipids, and steroids.
  • Hydrophobic molecules.
  • Important for energy storage, insulation, and cell membrane structure.
  • Fats (triglycerides) consist of glycerol and three fatty acids.
  • Saturated fats contain no double bonds.
  • Unsaturated fats contain one or more double bonds.
  • Phospholipids are major components of cell membranes.
  • Steroids include cholesterol and certain hormones.
• Proteins:
  • Polymers of amino acids.
  • Perform diverse functions: enzymes, structural components, transport, immunity, and signaling.
  • Amino acids contain an amino group, a carboxyl group, and a variable R group.
  • Polypeptides are chains of amino acids linked by peptide bonds.
  • Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.
• Nucleic Acids:
  • DNA and RNA.
  • Polymers of nucleotides.
  • Store and transmit genetic information.
  • Nucleotides consist of a sugar, a phosphate group, and a nitrogenous base.
  • DNA is double-stranded and contains the sugar deoxyribose.
  • RNA is single-stranded and contains the sugar ribose.
  • Nitrogenous bases in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T).
  • Nitrogenous bases in RNA: adenine (A), guanine (G), cytosine (C), and uracil (U).

Cell Structure and Function

• Cells are the fundamental unit of life.
• Two main types of cells: prokaryotic and eukaryotic.
• Prokaryotic cells lack a nucleus and other membrane-bound organelles.
• Eukaryotic cells have a nucleus and other membrane-bound organelles.
• Nucleus contains the cell's DNA and controls the cell's activities.
• Ribosomes synthesize proteins.
• Endoplasmic reticulum (ER) synthesizes and transports proteins and lipids.
• Golgi apparatus modifies, sorts, and packages proteins and lipids.
• Lysosomes break down cellular waste and debris.
• Mitochondria generate energy through cellular respiration.
• Chloroplasts carry out photosynthesis in plant cells.
• Cell membrane controls the movement of substances into and out of the cell.
• Cell wall provides support and protection to plant, fungal, and bacterial cells.

Membrane Structure and Function

• The cell membrane is a selectively permeable barrier.
• Composed of a phospholipid bilayer with embedded proteins.
• The fluid mosaic model describes the membrane as a dynamic structure with lipids and proteins moving laterally.
• Membrane proteins have various functions: transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix.
• Membrane transport mechanisms include passive and active transport.
• Passive transport requires no energy, including diffusion, osmosis, and facilitated diffusion.
• Active transport requires energy to move substances against their concentration gradients.
• Endocytosis and exocytosis transport large molecules across the membrane.

Metabolism

• Metabolism is the sum of all chemical reactions within an organism.
• Catabolism is the breakdown of complex molecules into simpler ones, releasing energy.
• Anabolism is the synthesis of complex molecules from simpler ones, requiring energy.
• Enzymes are biological catalysts that speed up chemical reactions.
• ATP (adenosine triphosphate) is the primary energy currency of the cell.
• Cellular respiration is the process of breaking down glucose to generate ATP, including glycolysis, pyruvate oxidation, citric acid cycle (Krebs cycle), and oxidative phosphorylation.
• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy, involving light-dependent reactions and the Calvin cycle.

Cell Communication

• Cells communicate through chemical signals in a process involving reception, transduction, and response.
• Types of signaling:
  • Endocrine: Hormones travel through the bloodstream to target cells.
  • Paracrine: Signals affect nearby cells.
  • Autocrine: Signals affect the same cell that produces them.
  • Direct contact: Gap junctions allow direct communication between cells.
• Signal transduction pathways convert extracellular signals into intracellular responses.
• G protein-coupled receptors, receptor tyrosine kinases, and ion channel receptors facilitate signal transduction.

Cell Cycle

• The cell cycle is the series of events a cell goes through from one division to the next.
• Interphase: Cell grows and prepares for division, including G1 phase, S phase (DNA replication), and G2 phase.
• Mitotic phase (M phase): Cell divides, including mitosis and cytokinesis.
• Mitosis: Division of the nucleus, including prophase, metaphase, anaphase, and telophase.
• Cytokinesis: Division of the cytoplasm.
• Regulation of the cell cycle involves checkpoints to ensure proper timing and completion of events.
• Cell cycle checkpoints: G1 checkpoint, G2 checkpoint, and M checkpoint.

Genetics

• Genetics is the study of heredity and genes.
• Genes are units of heredity made of DNA.
• Chromosomes are structures that carry genes.
• DNA replication is the process of making an identical copy of DNA.
• Transcription is the process of making RNA from DNA.
• Translation is the process of making protein from RNA.
• Gene expression: The process by which information encoded in a gene is used to synthesize a functional gene product.
• Mutations are changes in the DNA sequence.
• Meiosis is cell division that produces gametes (sex cells) with half the number of chromosomes as the parent cell.
• Sexual reproduction combines genetic material from two parents.
• Mendelian genetics describes principles of inheritance discovered by Gregor Mendel, including the law of segregation and the law of independent assortment.
• Non-Mendelian genetics includes inheritance patterns that do not follow Mendel's laws, such as linked genes, sex-linked genes, incomplete dominance, codominance, and polygenic inheritance.

Evolution

• Evolution describes change in the genetic makeup of a population over time.
• Natural selection describes the differential survival and reproduction of individuals with certain traits.
• Adaptation refers to inherited traits that enhance survival and reproduction in a specific environment.
• Evidence for evolution includes the fossil record, comparative anatomy, embryology, biogeography, and molecular biology.
• Mechanisms of evolution: Mutation, gene flow, genetic drift, and natural selection.
• Speciation is the process by which new species arise.
• Allopatric speciation occurs when geographic isolation leads to speciation.
• Sympatric speciation occurs in the same geographic area.
• Phylogeny is the evolutionary history of a species or group of species.

Classification of Living Things

• Taxonomy is the science of classifying and naming organisms.
• The Linnaean system is a hierarchical classification system.
• Domains: Bacteria, Archaea, and Eukarya.
• Kingdoms: Animalia, Plantae, Fungi, Protista, Archaebacteria, and Eubacteria.
• Binomial nomenclature is a two-part naming system consisting of genus and species.

Ecology

• Ecology is the study of the interactions between organisms and their environment.
• Population ecology studies population size, density, distribution, and dynamics.
• Community ecology studies interactions between different species in a community.
• Ecosystem ecology studies the flow of energy and cycling of nutrients in an ecosystem.
• Biomes are major types of ecosystems characterized by climate and dominant vegetation.
• Trophic levels indicate the position an organism occupies in a food chain or food web.
• Producers, consumers, and decomposers comprise trophic levels.
• Food chains and food webs show the flow of energy and nutrients through an ecosystem.
• Biodiversity is the variety of life in an ecosystem or the entire planet.
• Conservation biology studies preserving and protecting biodiversity.