Introduction to Biology

• Biology is the scientific study of life
• It explores the structure, function, growth, origin, evolution, distribution, and taxonomy of living organisms

Core Principles of Biology

• Cell theory: All living organisms are composed of cells
• Cells are the basic units of structure and function in living organisms
• All cells arise from pre-existing cells
• Gene theory: Traits are inherited through genes
• Genes are specific regions on DNA that code for particular traits
• Evolution: Life evolves over time through processes like natural selection
• Natural selection is a mechanism where organisms with advantageous traits are more likely to survive and reproduce
• Homeostasis: Living organisms maintain a stable internal environment
• This includes regulating temperature, pH, and other factors necessary for survival

Levels of Biological Organization

• Biosphere: The part of Earth where life exists, including land, water, and atmosphere
• Ecosystem: A community of living organisms (biotic factors) interacting with their physical environment (abiotic factors)
• Community: Populations of different species living and interacting in a specific area
• Population: A group of individuals of the same species living in the same area
• Organism: An individual living entity
• Organ System: A group of organs working together to perform specific functions
• Organ: A structure composed of different tissues working together to perform a specific function
• Tissue: A group of similar cells performing a specific function
• Cell: The basic structural and functional unit of life
• Organelle: A specialized subunit within a cell that has a specific function
• Molecule: A group of atoms bonded together

Classification of Living Organisms

• Taxonomy is the science of classifying and naming organisms
• The Linnaean system of classification uses a hierarchical structure
• Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
• The three domains of life are:
• Bacteria (prokaryotic microorganisms)
• Archaea (prokaryotic microorganisms distinct from bacteria)
• Eukarya (organisms with cells containing a nucleus)

Key Biological Molecules

• Carbohydrates: Primary source of energy for the body
• Monosaccharides (e.g., glucose, fructose) are simple sugars
• Polysaccharides (e.g., starch, glycogen, cellulose) are complex carbohydrates
• Lipids: Include fats, oils, and steroids
• Used for energy storage, insulation, and forming cell membranes
• Saturated fats have no double bonds, while unsaturated fats have one or more
• Proteins: Made up of amino acids
• Important for structure, enzymes, transport, and defense
• Enzymes are biological catalysts that speed up chemical reactions
• Nucleic Acids: DNA and RNA
• DNA stores genetic information
• RNA is involved in protein synthesis

Cell Structure and Function

• Prokaryotic Cells: Lack a nucleus and other membrane-bound organelles
• Bacteria and archaea are prokaryotes
• Have a cell wall, cell membrane, cytoplasm, ribosomes, and genetic material (DNA)
• Eukaryotic Cells: Contain a nucleus and other membrane-bound organelles
• Eukaryotes include protists, fungi, plants, and animals
• Organelles include the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and chloroplasts (in plants)

Cell Membrane

• The cell membrane is a selectively permeable barrier
• It controls what enters and exits the cell
• Composed of a phospholipid bilayer with embedded proteins
• Fluid mosaic model describes the structure and behavior of the cell membrane

Cellular Processes

• Photosynthesis: The process by which plants and some bacteria convert light energy into chemical energy in the form of glucose
• Occurs in chloroplasts
• Uses carbon dioxide, water, and light
• Produces glucose and oxygen
• Cellular Respiration: The process by which cells break down glucose to release energy in the form of ATP
• Occurs in mitochondria
• Uses glucose and oxygen
• Produces carbon dioxide, water, and ATP
• Mitosis: Cell division that results in two identical daughter cells
• Important for growth, repair, and asexual reproduction
• Consists of phases: prophase, metaphase, anaphase, and telophase
• Meiosis: Cell division that results in four genetically different daughter cells with half the number of chromosomes
• Important for sexual reproduction
• Consists of two rounds of division: meiosis I and meiosis II

Genetics

• Genes: Units of heredity composed of DNA
• Located on chromosomes
• DNA Structure: Double helix made of nucleotides
• Nucleotides consist of a sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, and thymine)
• DNA Replication: The process of copying DNA
• Ensures that each daughter cell receives a complete set of chromosomes
• Transcription: The process of synthesizing RNA from a DNA template
• mRNA carries genetic information from the nucleus to the ribosomes
• Translation: The process of synthesizing a protein from an mRNA template
• Occurs at the ribosomes
• Involves tRNA, which carries amino acids to the ribosome

Evolution and Natural Selection

• Evolution: Change in the genetic makeup of a population over time
• Natural Selection: The mechanism by which populations evolve
• Individuals with advantageous traits are more likely to survive and reproduce
• This leads to an increase in the frequency of those traits in the population
• Evidence for Evolution:
• Fossil record
• Comparative anatomy
• Embryology
• Molecular biology
• Biogeography

Ecology

• Ecology: The study of the interactions between organisms and their environment
• Population Ecology: Focuses on the size, density, distribution, and dynamics of populations
• Community Ecology: Examines the interactions between different species in a community
• Ecosystem Ecology: Studies the flow of energy and cycling of nutrients through ecosystems
• Biomes: Large geographic areas characterized by specific climate conditions, animal populations, and plant species

Ecological Interactions

• Competition: Organisms compete for limited resources
• Predation: One organism (the predator) consumes another organism (the prey)
• Symbiosis: Close interactions between two different species
• Mutualism (both benefit)
• Commensalism (one benefits, the other is unaffected)
• Parasitism (one benefits, the other is harmed)