Introduction to Biology: Core Principles and Organization

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

Core Principles of Biology

• Cell theory: all living organisms are composed of cells
• Gene theory: heredity occurs through genes, units of inheritance
• Evolution: populations evolve over time
• Homeostasis: living organisms maintain a stable internal environment

Levels of Biological Organization

• Molecules: atoms combine to form molecules, such as DNA and proteins
• Cells: the basic unit of life, consisting of organelles and other structures enclosed by a membrane
• Tissues: similar cells performing a specific function
• Organs: different tissues organized to perform specific functions
• Organ systems: organs working together
• Organisms: individual living entities
• Populations: groups of individuals of the same species in a given area
• Communities: populations of different species in a given area
• Ecosystems: communities and their nonliving environment
• Biosphere: all ecosystems combined – the regions of Earth inhabited by life

Chemistry of Life

• Living organisms are composed of organic molecules, which contain carbon
• Key organic molecules include carbohydrates, lipids, proteins, and nucleic acids
• Carbohydrates: provide energy and structural support
• Lipids: store energy, form cell membranes, and act as hormones
• Proteins: perform various functions, including enzymes, structural components, and transport
• Nucleic acids (DNA and RNA): carry genetic information

Cell Structure and Function

• Cells are either prokaryotic or eukaryotic
• Prokaryotic cells: lack a nucleus and other membrane-bound organelles (e.g., bacteria)
• Eukaryotic cells: contain a nucleus and other membrane-bound organelles (e.g., animal, plant, fungi, and protist cells)
• Key cell structures:
  • Plasma membrane: regulates the movement of substances in and out of the cell
  • Nucleus: contains the cell's DNA
  • Ribosomes: synthesize proteins
  • Endoplasmic reticulum (ER): involved in protein and lipid synthesis
  • Golgi apparatus: modifies, sorts, and packages proteins
  • Mitochondria: produce energy through cellular respiration
  • Chloroplasts (in plant cells): conduct photosynthesis
  • Lysosomes: break down waste materials and cellular debris

Energy and Metabolism

• Metabolism: all chemical reactions that occur in an organism
• Enzymes: proteins that catalyze (speed up) chemical reactions
• Cellular respiration: process by which cells break down glucose to produce ATP, the energy currency of the cell
• Photosynthesis: process by which plants and other organisms convert light energy into chemical energy in the form of glucose

Genetics

• Genes: units of heredity made of DNA
• DNA: deoxyribonucleic acid, the molecule that carries genetic information
• DNA structure: double helix composed of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base (adenine, thymine, guanine, or cytosine)
• RNA: ribonucleic acid, involved in protein synthesis
• Gene expression: the process by which the information encoded in a gene is used to synthesize a functional gene product (protein or RNA)
• Transcription: DNA is transcribed into mRNA
• Translation: mRNA is translated into protein at the ribosome

Cell Division

• Cell division is essential for growth, repair, and reproduction
• Mitosis: cell division that results in two identical daughter cells; used for growth and repair
• Meiosis: cell division that results in four daughter cells with half the number of chromosomes; used for sexual reproduction

Evolution

• Evolution: change in the heritable characteristics of biological populations over successive generations
• Natural selection: differential survival and reproduction of individuals with certain traits
• Adaptation: inherited traits that enhance an organism's survival and reproduction in a specific environment
• Evidence for evolution:
  • Fossil record
  • Comparative anatomy
  • Embryology
  • Biogeography
  • Molecular biology

Ecology

• Ecology is the study of the interactions between organisms and their environment
• Population ecology: studies the factors that affect population size and density
• Community ecology: studies the interactions between different species in a community
• Ecosystem ecology: studies the flow of energy and cycling of nutrients in an ecosystem
• Key ecological concepts:
  • Biotic factors: living components of an ecosystem
  • Abiotic factors: nonliving components of an ecosystem (e.g., temperature, water, sunlight)
  • Food webs: illustrate the flow of energy through an ecosystem
  • Trophic levels: position an organism occupies in a food web (e.g., producers, consumers, decomposers)
  • Biomes: large geographic areas characterized by specific climate conditions and plant communities

Biological Diversity

• Biodiversity: the variety of life at all levels of biological organization
• Three domains of life:
  • Bacteria: prokaryotic microorganisms
  • Archaea: prokaryotic microorganisms that often live in extreme environments
  • Eukarya: organisms with eukaryotic cells (protists, fungi, plants, and animals)
• Classification of organisms:
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

Plant Biology

• Plants are multicellular, eukaryotic organisms that conduct photosynthesis
• Key plant structures:
  • Roots: anchor the plant and absorb water and nutrients
  • Stems: support the plant and transport water and nutrients
  • Leaves: conduct photosynthesis
  • Flowers: involved in sexual reproduction
• Plant reproduction:
  • Sexual reproduction: involves pollination and fertilization
  • Asexual reproduction: involves vegetative propagation (e.g., cuttings, grafting)

Animal Biology

• Animals are multicellular, eukaryotic organisms that are heterotrophic (obtain nutrients by consuming other organisms)
• Key animal characteristics:
  • Movement
  • Sensory systems
  • Nervous system
  • Endocrine system
  • Digestive system
  • Respiratory system
  • Circulatory system
  • Excretory system
  • Reproductive system
• Animal classification: based on body plan, development, and genetic characteristics

Microbiology

• Microbiology is the study of microorganisms, including bacteria, archaea, viruses, fungi, and protists
• Microorganisms play important roles in:
  • Nutrient cycling
  • Decomposition
  • Disease
  • Biotechnology

Human Biology

• Human biology is the study of the human body, including its anatomy, physiology, and genetics
• Key human organ systems:
  • Integumentary system (skin)
  • Skeletal system (bones)
  • Muscular system (muscles)
  • Nervous system (brain, spinal cord, nerves)
  • Endocrine system (glands and hormones)
  • Cardiovascular system (heart and blood vessels)
  • Lymphatic system (immune system)
  • Respiratory system (lungs)
  • Digestive system (stomach, intestines)
  • Urinary system (kidneys, bladder)
  • Reproductive system (ovaries, testes)

Biotechnology

• Biotechnology involves the use of biological systems to create products or processes
• Applications of biotechnology:
  • Medicine (e.g., vaccines, gene therapy)
  • Agriculture (e.g., genetically modified crops)
  • Environmental science (e.g., bioremediation)
  • Forensics (e.g., DNA fingerprinting)