Biology
Cell to ecosystem, plus the body systems AP Biology leaves out — with natural selection run as a population shifting over generations.
21 units · 146 topics · 608 questions
The molecules and properties that make life possible, from water's odd behavior to the four classes of biological macromolecules.
What Makes Something Alive · Levels of Biological Organization · Water and the Properties of Life · Carbohydrates · +4 more
Inside the cell: the organelles, membranes, and structures every living cell depends on to survive.
Cell Theory and the Discovery of Cells · Prokaryotic vs Eukaryotic Cells · The Nucleus and Genetic Control · Ribosomes, the ER, and the Golgi Apparatus · +5 more
How a paper-thin membrane decides exactly what gets into a cell and what gets kept out.
The Phospholipid Bilayer · Selective Permeability · Diffusion · Osmosis and Tonicity · +3 more
How a plant turns sunlight, water, and air into the sugar that fuels nearly every food chain on Earth.
Why Plants Need Sunlight · Chloroplast Structure and Pigments · The Light-Dependent Reactions · The Calvin Cycle · +1 more
How a cell burns the sugar built by photosynthesis to generate the ATP it actually runs on.
Why Cells Break Down Glucose · Glycolysis · The Krebs Cycle · The Electron Transport Chain and ATP Synthase · +2 more
How one cell becomes two identical cells through mitosis, and how sex cells get half the usual chromosome count through meiosis.
The Cell Cycle and Interphase · Mitosis: Making Identical Copies · Cytokinesis in Plant and Animal Cells · Why Sex Cells Need Meiosis · +4 more
How the code stored in DNA gets copied, read, and built into the proteins that do a cell's actual work.
DNA Structure and the Double Helix · DNA Replication · From DNA to RNA: Transcription · The Genetic Code and Codons · +3 more
Mendel's laws, Punnett squares, and how real human traits like blood type and color blindness get passed down.
Mendel and the Birth of Genetics · Genotype, Phenotype, and Alleles · Punnett Squares and Monohybrid Crosses · Dihybrid Crosses and Independent Assortment · +5 more
How scientists read, cut, copy, and edit DNA -- from a police lab's gel to a CRISPR-edited genome.
What Genetic Engineering Actually Does · Selective Breeding and Artificial Selection · Gel Electrophoresis · DNA Fingerprinting · +2 more
Why populations change over generations, and the fossil, anatomical, and molecular evidence that it happened.
Darwin and the Idea of Natural Selection · Variation and the Struggle to Survive · How Natural Selection Changes a Population · Directional, Stabilizing, and Disruptive Selection · +6 more
How millions of species get sorted into one family tree, from the three domains down to a single genus and species.
Why Scientists Classify Living Things · The Levels of Classification · The Three Domains of Life · The Six Kingdoms · +4 more
Why a virus isn't alive, how bacteria multiply, and what makes the microbes living inside you your allies.
Why a Virus Isn't Considered Alive · Viral Structure and Replication · How Viruses Cause Disease · Bacterial Structure and Reproduction · +2 more
How a plant standing still solves every problem an animal solves by moving: feeding, breathing, and reproducing.
Plant Structure: Roots, Stems, and Leaves · How Water Moves Up a Plant · Gas Exchange in Leaves · Plant Reproduction: Flowers, Pollination, and Seeds · +2 more
How the body senses when something is off balance and pulls it back -- or, in labor and clotting, pushes it further.
What Homeostasis Actually Means · Negative Feedback · Positive Feedback · How Body Systems Cooperate to Maintain Balance
The path food takes from your first bite to the nutrients your cells actually use, and how your kidneys clean your blood.
How Digestion Breaks Food Into Usable Molecules · The Journey of Food Through the Digestive Tract · The Role of the Liver and Pancreas in Digestion · Absorption in the Small Intestine · +2 more
How your heart, blood vessels, and lungs work together to get oxygen from the air into every one of your cells.
Why the Body Needs a Circulatory System · The Structure of the Heart and How It Pumps · Arteries, Veins, and Capillaries · Blood Composition and Function · +3 more
How electrical nerve signals and chemical hormones each carry messages across your body, on very different timescales.
The Structure of a Neuron · How a Nerve Impulse Travels · Synapses and Neurotransmitters · The Brain and Spinal Cord · +3 more
How your body tells its own cells apart from invaders, and fights off the invaders without fighting itself.
The Body's First Line of Defense · Innate Immunity: Inflammation and White Blood Cells · Adaptive Immunity: B Cells and Antibodies · T Cells and Cell-Mediated Immunity · +2 more
How bones, joints, and muscles turn a chemical signal into the physical motion of a body moving through space.
The Structure and Function of Bone · Joints and Range of Motion · How Skeletal Muscles Move Bones · The Sliding Filament Model of Muscle Contraction · +1 more
How a body produces the next generation, from sperm and egg to a fully developed fetus ready to be born.
The Male Reproductive System · The Female Reproductive System and the Menstrual Cycle · Fertilization and Early Development · Pregnancy and Fetal Development
How energy and matter cycle through an ecosystem, and what happens to the whole web when humans change one part of it.
Levels of Ecological Organization · Food Chains and Food Webs · Energy Flow and Trophic Pyramids · The Carbon and Nitrogen Cycles · +8 more