Introduction to Biology

• Biology is the scientific study of life
• It explores the structure, function, growth, origin, evolution, distribution, and taxonomy of living organisms
• It is a broad field comprising many specialized disciplines that cover scales from sub-cellular to ecosystems

Core Principles of Biology

• Cell theory: The cell is the basic unit of life
• Gene theory: Hereditary information is encoded in DNA and genes
• Evolution: Life evolves over time through natural selection
• Homeostasis: Living organisms maintain a stable internal environment
• Thermodynamics: Life depends on the flow of energy

Branches of Biology

• Biochemistry: Study of the chemical substances and processes in living organisms
• Molecular biology: Study of the structure and function of biological macromolecules (e.g., proteins, nucleic acids)
• Cell biology: Study of cell structure, function, and behavior
• Genetics: Study of heredity and variation in organisms
• Evolutionary biology: Study of the evolutionary processes that produce the diversity of life on Earth
• Ecology: Study of the interactions of organisms with each other and their environment
• Physiology: Study of the normal functions of living organisms and their parts
• Anatomy: Study of the structure of living organisms
• Microbiology: Study of microorganisms, such as bacteria, viruses, fungi, and protozoa
• Botany: Study of plants, including their physiology, structure, genetics, ecology, distribution, classification, and economic importance
• Zoology: Study of animals, including their classification, physiology, development, and behavior
• Marine biology: Study of marine organisms and their interactions with the ocean environment

Chemical Basis of Life

• Living organisms are composed of organic molecules, primarily carbohydrates, lipids, proteins, and nucleic acids
• Carbon is the backbone of these molecules, due to its ability to form stable bonds with other atoms
• Water is essential for life, due to its properties as a solvent, its high heat capacity, and its role in many biochemical reactions

Cell Structure and Function

• Cells are the basic structural and functional units of life
• Prokaryotic cells (bacteria and archaea) lack a nucleus and other membrane-bound organelles
• Eukaryotic cells (protists, fungi, plants, and animals) contain a nucleus and other membrane-bound organelles
• Major cell organelles include the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and chloroplasts (in plant cells)
• The cell membrane is a selectively permeable barrier that regulates the passage of substances into and out of the cell

Energy and Metabolism

• Metabolism is the sum of all chemical reactions that occur within a living organism
• Catabolism involves the breakdown of complex molecules into simpler ones, releasing energy
• Anabolism involves the synthesis of complex molecules from simpler ones, requiring energy
• Enzymes are biological catalysts that speed up biochemical reactions
• ATP (adenosine triphosphate) is the main energy currency of cells
• Photosynthesis is the process by which plants and some bacteria convert light energy into chemical energy in the form of glucose
• Cellular respiration is the process by which cells break down glucose to generate ATP

Genetics

• Genes are units of heredity that contain the instructions for building proteins
• DNA (deoxyribonucleic acid) is the molecule that carries genetic information
• DNA is composed of nucleotides, each containing a sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine)
• RNA (ribonucleic acid) is involved in protein synthesis and gene regulation
• DNA replication is the process by which DNA is copied
• Transcription is the process by which RNA is synthesized from a DNA template
• Translation is the process by which proteins are synthesized from an RNA template

Evolution

• Evolution is the change in the heritable characteristics of biological populations over successive generations
• Natural selection is the primary mechanism of evolution
• Mutations are changes in the DNA sequence that can lead to new traits
• Genetic drift is the random change in allele frequencies in a population
• Gene flow is the transfer of genetic variation from one population to another
• Speciation is the process by which new species arise

Ecology

• Ecology is the study of the interactions of organisms with each other and their environment
• Ecosystems are communities of organisms interacting with their physical environment
• Populations are groups of individuals of the same species living in the same area
• Communities are groups of different species living in the same area
• The biosphere is the sum of all ecosystems on Earth
• Energy flows through ecosystems from producers (autotrophs) to consumers (heterotrophs)
• Nutrients cycle through ecosystems
• Biomes are large-scale communities characterized by distinct climate conditions and dominant plant life

Classification of Living Things

• Taxonomy is the science of classifying organisms
• The Linnaean system of classification uses a hierarchical system of categories: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species
• The three domains of life are Bacteria, Archaea, and Eukarya
• The kingdoms within Eukarya include Protista, Fungi, Plantae, and Animalia

Viruses

• Viruses are acellular entities consisting of a nucleic acid genome surrounded by a protein coat (capsid)
• Viruses are obligate intracellular parasites, meaning they can only replicate inside a host cell
• Viral replication involves attachment to the host cell, entry into the cell, replication of the viral genome, assembly of new viral particles, and release from the cell

Biodiversity

• Biodiversity is the variety of life at all levels of biological organization
• It includes genetic diversity, species diversity, and ecosystem diversity
• Biodiversity is essential for ecosystem functioning and provides many benefits to humans
• Habitat loss, pollution, climate change, and invasive species are major threats to biodiversity

Human Biology

• Human biology is the study of the human body, its structure, function, and evolution
• Humans are vertebrates belonging to the class Mammalia
• The human body is composed of cells, tissues, organs, and organ systems
• The major organ systems include the circulatory, respiratory, digestive, excretory, nervous, endocrine, skeletal, muscular, and reproductive systems

Reproduction and Development

• Reproduction is the process by which organisms produce offspring
• Asexual reproduction involves a single parent and produces genetically identical offspring
• Sexual reproduction involves two parents and produces genetically diverse offspring
• Development is the process by which an organism grows and differentiates from a single cell into a complex multicellular organism
• In humans, fertilization occurs when a sperm cell fuses with an egg cell, forming a zygote
• The zygote undergoes cleavage, gastrulation, and organogenesis to form an embryo
• The embryo develops into a fetus, which is born after a period of gestation

Disease and Immunity

• Disease is any condition that impairs the normal functioning of the body
• Infectious diseases are caused by pathogens such as bacteria, viruses, fungi, and parasites
• The immune system protects the body from pathogens and other harmful substances
• The innate immune system provides a rapid, non-specific response to infection
• The adaptive immune system provides a slower, more specific response to infection
• Vaccines stimulate the immune system to produce antibodies against specific pathogens

Plant Biology

• Plants are multicellular, eukaryotic organisms that belong to the kingdom Plantae
• They are autotrophs, meaning they produce their own food through photosynthesis
• Plants have cell walls made of cellulose
• Vascular plants have specialized tissues for transporting water and nutrients
• Non-vascular plants lack these tissues and are typically smaller
• Flowers are the reproductive structures of angiosperms (flowering plants)

Animal Biology

• Animals are multicellular, eukaryotic organisms that belong to the kingdom Animalia
• They are heterotrophs, meaning they obtain their food by consuming other organisms
• Animals lack cell walls
• Animals are classified into various phyla based on their body plan and other characteristics
• Major animal phyla include Porifera (sponges), Cnidaria (jellyfish), Platyhelminthes (flatworms), Nematoda (roundworms), Annelida (segmented worms), Mollusca (snails, clams, squids), Arthropoda (insects, spiders, crustaceans), Echinodermata (starfish), and Chordata (vertebrates)