Biology Explained
Life from molecules to ecosystems.
Cells
Cell structure, organelles and division.
How Cell Membranes Work: Structure, Permeability and Transport
How the phospholipid bilayer, cholesterol and membrane proteins control what enters and leaves a cell, explained step by step.
CellsHow Mitosis Divides a Cell in Two: Phases, Checkpoints and Results
A phase-by-phase guide to mitosis, the division that copies a cell's chromosomes and produces two identical daughter cells.
Genetics
DNA, genes, inheritance and gene editing.
How DNA Replication Works: Enzymes, Strands and Accuracy
How cells copy DNA: helicase opens the helix, polymerase builds new strands 5 to 3, and proofreading keeps errors rare.
GeneticsHow Mendelian Inheritance Works: Alleles, Crosses and Ratios
Gregor Mendel's two laws explained with Punnett squares for monohybrid, dihybrid and test crosses, plus the limits of the rules.
Evolution
Natural selection and the history of life.
Genetic Drift Explained: Chance, Bottlenecks and Founder Effects
How random sampling changes allele frequencies in small populations, with bottleneck and founder effect examples and a size table.
EvolutionHow Natural Selection Works: Variation, Fitness and Adaptation
Natural selection explained: four requirements, directional, stabilizing and disruptive modes, and examples from finches and bacteria.
Human Body
Organ systems and how the body works.
How the Heart Pumps Blood: Chambers, Valves and the Cardiac Cycle
How the four heart chambers, one-way valves and electrical pacemaker cells move blood through the lungs and body, explained step by step.
BodyHow the Kidneys Filter Blood: Nephrons, Reabsorption and Urine
How each kidney's million nephrons filter blood, reclaim water and nutrients, and remove waste to form urine, explained step by step.
Ecology
Ecosystems, food webs and biodiversity.
How Food Webs Work: Trophic Levels, Energy Loss and Keystone Predators
How food webs connect producers, consumers and decomposers, why energy shrinks at each level, and how predators shape whole ecosystems.
EcologyHow the Carbon Cycle Works: Reservoirs, Fluxes and Turnover Times
How carbon moves between air, oceans, plants, soil and rock, why each reservoir holds a different amount, and how fast carbon cycles through each one.
Microbiology
Bacteria, viruses and the microbiome.
How Bacteria Reproduce: Binary Fission, Doubling Time and Gene Sharing
How a single bacterial cell copies its chromosome and splits in two, why colonies grow exponentially, and how bacteria share genes that spread traits.
MicrobesHow Viruses Replicate Inside Cells: Lytic, Lysogenic and Retroviral Cycles
How viruses attach to host cells, hijack their machinery to copy genomes and build new particles, and why lytic, lysogenic and retroviral cycles differ.