Biology

Biology is the study of life, from the chemistry inside a single cell to the ecology of the whole planet. This book is the two-semester majors course: it starts with the chemical building blocks of living things and the cell, moves through genetics and evolution, surveys the diversity of life, and closes with how plants and animals are built and how ecosystems work.

Chapters

Unit 1: The Chemistry of Life

• The Study of Life — what biology is, how science works (observation, hypothesis, experiment, theory), and the properties, levels of organization, and evolutionary connections shared by all living things.
• The Chemical Foundation of Life — atoms, isotopes, ions, and chemical bonds; the properties of water that make life possible; and carbon’s hydrocarbons, isomers, and functional groups.
• Biological Macromolecules — how monomers join into polymers, and the structures and roles of carbohydrates, lipids, proteins, and nucleic acids.

Unit 2: The Cell

• Cell Structure — how cells are studied, prokaryotic and eukaryotic cells, the organelles and endomembrane system, the cytoskeleton, and the junctions that connect cells.
• Structure and Function of Plasma Membranes — the fluid mosaic model, passive transport (diffusion, osmosis, tonicity), active transport, and bulk transport.
• Metabolism — energy and metabolic pathways, kinetic, potential, free, and activation energy, the laws of thermodynamics, ATP, and enzymes.
• Cellular Respiration — electron carriers, glycolysis, pyruvate oxidation and the citric acid cycle, oxidative phosphorylation, fermentation, the connections between metabolic pathways, and how respiration is regulated.
• Photosynthesis — an overview, the light-dependent reactions, and the Calvin cycle.
• Cell Communication — signaling molecules and receptors, how a signal propagates and is responded to, and signaling in single-celled organisms.
• Cell Reproduction — chromosomes and genomes, the cell cycle and its control, cancer, and binary fission.

Unit 3: Genetics

• Meiosis and Sexual Reproduction — how the two divisions of meiosis halve the chromosome number and shuffle alleles through crossover and random assortment, and why the variation sexual reproduction creates is an evolutionary advantage across the three life-cycle types.
• Mendel’s Experiments and Heredity — Mendel’s pea-plant experiments and the laws of probability; genotype, phenotype, and the patterns of dominance; and the laws of segregation and independent assortment, with linkage and epistasis as extensions.
• Modern Understandings of Inheritance — the chromosomal theory of inheritance, genetic linkage and recombination-based chromosome maps, and the chromosomal errors — nondisjunction, aneuploidy, and structural rearrangements — behind inherited disorders.
• DNA Structure and Function — the experiments that proved DNA is the hereditary material, the double helix and how DNA is packaged and sequenced, semi-conservative replication in prokaryotes and eukaryotes with the enzymes that carry it out, and the repair mechanisms that catch replication errors and mutations.
• Genes and Proteins — the genetic code and its degeneracy, prokaryotic and eukaryotic transcription, how eukaryotes process pre-mRNAs, rRNAs, and tRNAs, and how ribosomes translate an mRNA into a polypeptide.
• Gene Expression — the levels at which prokaryotes and eukaryotes regulate gene expression, from operons through epigenetic, transcriptional, post-transcriptional, translational, and post-translational control, and how failures of that regulation drive cancer.
• Biotechnology and Genomics — the techniques of manipulating DNA — extraction, gel electrophoresis, PCR, cloning, and genetic engineering of plants and animals — and how genetic and physical maps, whole-genome sequencing, and the growing fields of genomics, metagenomics, pharmacogenomics, and proteomics turn genome information into medicine, agriculture, and industry.

Unit 4: Evolutionary Processes

• Evolution and the Origin of Species — how scientists arrived at the theory of evolution by natural selection, what homologous and vestigial structures reveal about common ancestry, how prezygotic and postzygotic barriers keep species apart and allopatric and sympatric speciation and adaptive radiation give rise to new ones, and what happens — and how quickly — when diverging species reconnect in a hybrid zone.
• The Evolution of Populations — how population genetics and the Hardy-Weinberg principle describe evolution as a change in a population’s allele frequencies, the forces — natural selection, genetic drift, gene flow, mutation, and nonrandom mating — that drive it, and the ways natural selection shapes a population’s variation.
• Phylogenies and the History of Life — how phylogenetic trees record evolutionary relationships, how taxonomy classifies organisms and cladistics builds trees from shared derived characters and molecular data under maximum parsimony, and how horizontal gene transfer and genome fusion complicate the classic tree of life into webs and rings.

Unit 5: Biological Diversity

• Viruses — how viruses were discovered, are built, and are classified, the lytic and lysogenic replication cycles and the plant and animal diseases viruses cause, vaccines and antiviral drugs, and the acellular prions and viroids.
• Prokaryotes: Bacteria and Archaea — the origins and extremophile diversity of prokaryotes, how bacterial and archaeal cells are built and differ, the nutritional types and the carbon and nitrogen cycles, the bacterial diseases of history and today, and the prokaryotes that fix nitrogen, share our bodies, make our food, and clean up pollution.
• Protists — the endosymbiotic origin of eukaryotes, the structural and metabolic variety of protists, the six eukaryotic supergroups and their representative members, and the roles of protists as producers, decomposers, and parasites.
• Fungi — the shared traits, mycelium, nutrition, and reproduction of fungi, their five phyla, their roles as decomposers and mutualists, the fungal diseases of plants and humans, and fungi in food, industry, medicine, and research.
• Seedless Plants — the adaptations that carried plants onto land, the green algae closest to them, the liverworts, hornworts, and mosses, and the club mosses, horsetails, whisk ferns, and ferns with their vascular tissue, roots, leaves, and life cycle.
• Seed Plants — how seeds and pollen freed plants from water, the gymnosperms with their cones and naked seeds, the angiosperms with their flowers, double fertilization, and fruit, monocots and eudicots, and the role of seed plants in herbivory, pollination, food, and medicine.
• Introduction to Animal Diversity — the features that define animals, embryonic development and the Hox genes, symmetry, germ layers, body cavities and protostome versus deuterostome development, the modern animal phylogeny, and the Ediacaran, Cambrian, and later history of the animal kingdom.
• Invertebrates — sponges, cnidarians, the lophotrochozoan flatworms, rotifers, nemerteans, mollusks, and annelids, the ecdysozoan nematodes, tardigrades, and arthropods, and the invertebrate deuterostomes: the echinoderms and the invertebrate chordates.
• Vertebrates — the chordate body plan and the vertebrate phylogeny, the jawless and jawed fishes, amphibians and the move onto land, the amniotic egg and the reptiles, the flight adaptations of birds, the mammals and their clades, and the evolution of primates and hominins.

Unit 6: Plant Structure and Function

• Plant Form and Physiology — the shoot and root systems and the meristematic, dermal, vascular, and ground tissues, the anatomy and growth of stems, roots, and leaves and their modifications, water potential, transpiration, and the transport of water and photosynthates, and how plants sense and respond to light, gravity, touch, hormones, and attack.
• Soil and Plant Nutrition — the essential macronutrients and micronutrients, how soil forms and is layered into horizons, and the nutritional adaptations of parasites, saprophytes, epiphytes, and insectivorous plants, mycorrhizae, and nitrogen-fixing root nodules.
• Plant Reproduction — the flower, its whorls, and the development of pollen and the embryo sac, pollination by wind, water, insects, birds, and bats, double fertilization, seed and fruit development and dispersal, and asexual reproduction, grafting, cuttings, and plant life spans.

Unit 7: Animal Structure and Function

• The Animal Body: Basic Form and Function — body plans, symmetry, and the limits diffusion and metabolism place on size and shape, the four primary tissue types and their subtypes, and homeostasis, feedback loops, and thermoregulation.
• Animal Nutrition and the Digestive System — the digestive systems of invertebrates, birds, ruminants, and humans, the essential nutrients, vitamins, and minerals of a balanced diet and how food is converted to energy, the ingestion, digestion, absorption, and elimination of carbohydrates, proteins, and lipids, and the neural and hormonal regulation of digestion.
• The Nervous System — neurons and glial cells, resting and action potentials and chemical and electrical synapses, the brain, spinal cord, and meninges of the central nervous system, the autonomic and sensory-somatic divisions of the peripheral nervous system, and neurodegenerative, neurodevelopmental, and other neurological disorders.
• Sensory Systems — how receptors transduce stimuli and the brain perceives them, the mechanoreceptors and nociceptors of the skin, taste and smell, hearing and the vestibular sense, and the path of light through the eye to the visual cortex.
• The Endocrine System — the lipid-derived, amino acid-derived, and peptide hormones, intracellular and plasma membrane hormone receptors and signaling pathways, the hormonal regulation of excretion, reproduction, metabolism, blood calcium, growth, and stress, humoral, hormonal, and neural control of hormone release, and the endocrine glands.
• The Musculoskeletal System — hydrostatic skeletons, exoskeletons, and the axial and appendicular endoskeleton, bone tissue, cells, growth, and remodeling, the structural and functional classes of joints and the movements they allow, and the sliding-filament model of muscle contraction and locomotion.
• The Respiratory System — gas exchange across skin, gills, tracheae, and lungs, lung volumes and capacities and the partial pressures that drive diffusion, the mechanics and regulation of breathing, and the transport of oxygen and carbon dioxide in blood.
• The Circulatory System — open and closed circulatory systems and the vertebrate heart plans, the cellular and plasma components of blood, the mammalian heart, its cycle and conduction, and the vessels, and how blood flow and blood pressure are regulated.
• Osmotic Regulation and Excretion — osmoregulation and osmotic balance, the kidney and nephron and the three steps of urine formation, the excretory systems of other animals, the nitrogenous wastes and why animals differ in which they make, and the hormones that control kidney function.
• The Immune System — the innate barriers, cells, and complement system, the adaptive response of T cells, B cells, and memory, antibody structure, classes, and function, and hypersensitivities, autoimmunity, and immunodeficiency.
• Animal Reproduction and Development — asexual and sexual reproduction and external and internal fertilization, human reproductive anatomy and gametogenesis, the hormonal control of reproduction, pregnancy, birth, and contraception, and fertilization, cleavage, gastrulation, organogenesis, and axis formation in the embryo.

Unit 8: Ecology

• Ecology and the Biosphere — the levels of ecological study, biogeography and the abiotic factors that set species distributions, the terrestrial and aquatic biomes, and climate, weather, and the causes and effects of global climate change.
• Population and Community Ecology — population size, density, dispersion, and demography, life histories, exponential and logistic growth and its limits, population regulation, human population growth, community interactions and succession, and the proximate and ultimate causes of animal behavior.
• Ecosystems — the types of ecosystems and how ecologists model them, food chains and food webs, how energy flows and is lost between trophic levels, ecological pyramids, and the biogeochemical cycles of water, carbon, nitrogen, phosphorus, and sulfur and how human activity disrupts them.
• Conservation Biology and Biodiversity — how biodiversity is measured and where it is concentrated, the five mass extinctions and today’s extinction rates, why biodiversity matters to human life, the threats of habitat loss, overharvesting, exotic species, and climate change, and the laws, preserves, restoration, and captive breeding that protect it.

About this edition

This book is adapted from OpenStax Biology 2e by Mary Ann Clark, Jung Choi, Matthew Douglas, and OpenStax, © OpenStax, licensed under CC BY-NC-SA 4.0. Access the original for free at openstax.org. Every section page records its own changes from the source; figures are the source’s own, re-encoded for the web with their credits kept in the captions.