Introduction to Biology

• Biology is the scientific study of life
• It explores living organisms' structure, function, growth, origin, evolution, and distribution
• It encompasses diverse fields like anatomy, physiology, cell biology, genetics, ecology, and evolutionary biology

Characteristics of Life

• All living organisms share several key characteristics
• Organization: Living things have a high level of organization, from atoms to molecules to cells to tissues to organs to organ systems to organisms
• Metabolism: The sum of chemical reactions within an organism, including catabolism (breaking down molecules) and anabolism (building molecules)
• Reproduction: The ability to produce offspring, either sexually or asexually
• Growth and Development: Living organisms increase in size and complexity over time
• Response to Stimuli: The ability to react to environmental changes
• Adaptation: The capacity to change and evolve in response to environmental pressures
• Homeostasis: The maintenance of a stable internal environment

Cell Biology

• The cell is the basic unit of life
• All living organisms are composed of one or more cells
• Cells are responsible for carrying out all life processes
• Two main cell types exist: prokaryotic and eukaryotic
• Prokaryotic cells: Simpler, smaller cells lacking a nucleus and other membrane-bound organelles (e.g., bacteria and archaea)
• Eukaryotic cells: More complex, larger cells with a nucleus and other membrane-bound organelles (e.g., plants, animals, fungi, and protists)
• Key cell structures include:
• Plasma membrane: A selectively permeable barrier that surrounds the cell
• Cytoplasm: The gel-like substance within the cell containing the organelles
• Nucleus: The control center of the cell, containing the DNA
• Ribosomes: Sites of protein synthesis
• Endoplasmic reticulum: A network of membranes involved in protein and lipid synthesis
• Golgi apparatus: Modifies, sorts, and packages proteins and lipids
• Mitochondria: The powerhouses of the cell, responsible for generating energy (ATP) through cellular respiration
• Chloroplasts (in plant cells): Sites of photosynthesis, where light energy is converted into chemical energy
• Lysosomes: Contain enzymes for breaking down cellular waste

Genetics

• Genetics is the study of heredity and variation
• Genes are units of heredity with instructions for building proteins
• Genes are composed of DNA (deoxyribonucleic acid)
• DNA is a double-stranded helix containing the genetic code
• The genetic code is based on four nucleotide bases: adenine (A), guanine (G), cytosine (C), and thymine (T)
• DNA replication is the process of copying DNA
• Transcription is the process of converting DNA into RNA (ribonucleic acid)
• Translation is the process of converting RNA into protein
• Mutations are changes in the DNA sequence that can lead to genetic variation
• Mendelian genetics: The study of how traits are inherited from parents to offspring
• Chromosomes: Structures within the nucleus that contain DNA
• Humans have 46 chromosomes arranged in 23 pairs

Evolution

• Evolution is the process of change in the heritable characteristics of biological populations over successive generations
• Natural selection: Charles Darwin's proposed mechanism of evolution, where individuals with advantageous traits are more likely to survive and reproduce
• Adaptation: The process by which populations become better suited to their environment over time
• Evidence for evolution includes:
• Fossil record: The remains of organisms that lived in the past
• Comparative anatomy: The study of similarities and differences in the anatomy of different species
• Embryology: The study of the development of embryos
• Molecular biology: The study of DNA and protein sequences
• Biogeography: The study of the distribution of species around the world
• Speciation: The process by which new species arise

Ecology

• Ecology is the study of the interactions between organisms and their environment
• Ecosystem: A community of living organisms (biotic factors) interacting with their physical environment (abiotic factors)
• Population: A group of individuals of the same species living in the same area
• Community: A group of different species living in the same area
• Biosphere: The sum of all ecosystems on Earth
• Key ecological concepts include:
• Energy flow: The movement of energy through an ecosystem
• Food webs: Interconnected food chains that show the flow of energy in an ecosystem
• Nutrient cycling: The movement of essential elements (e.g., carbon, nitrogen, phosphorus) through an ecosystem
• Population dynamics: The study of how populations change in size and composition over time
• Community ecology: The study of the interactions between different species in a community
• Ecosystem ecology: The study of the flow of energy and nutrients through ecosystems
• Conservation biology: The study of how to protect biodiversity and conserve natural resources

Classification of Living Things

• Taxonomy: The science of classifying and naming organisms
• The Linnaean system of classification uses a hierarchical system:
• Domain: The broadest category (Archaea, Bacteria, Eukarya)
• Kingdom: (e.g., Animalia, Plantae, Fungi, Protista)
• Phylum
• Class
• Order
• Family
• Genus
• Species: The most specific category; a group of organisms that can interbreed and produce fertile offspring
• Binomial nomenclature: A system of naming organisms using two names: the genus and the species (e.g., Homo sapiens)

Key Biological Molecules

• Carbohydrates: Provide energy and structural support (e.g., sugars, starches, cellulose)
• Lipids: Store energy, form cell membranes, and act as hormones (e.g., fats, oils, phospholipids, steroids)
• Proteins: Perform a wide range of functions, including catalyzing reactions, transporting molecules, and providing structural support (e.g., enzymes, antibodies, hormones)
• Nucleic acids: Store and transmit genetic information (e.g., DNA, RNA)

Biological Processes

• Photosynthesis: The process by which plants use sunlight to convert carbon dioxide and water into glucose and oxygen
• Cellular respiration: The process by which cells break down glucose to release energy in the form of ATP
• Mitosis: Cell division that results in two identical daughter cells
• Meiosis: Cell division that results in four daughter cells with half the number of chromosomes (involved in sexual reproduction)
• Osmosis: The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration
• Diffusion: The movement of molecules from an area of high concentration to an area of low concentration
• Active transport: The movement of molecules across a cell membrane against their concentration gradient, requiring energy

Biology is the scientific study of life, exploring structure, function, growth, origin, evolution, and distribution. Living organisms share characteristics like organization, metabolism, reproduction, growth, response to stimuli and adaptation.