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Learning path · 19 parts

Life: Molecules to Organisms

Start with the principle that organises all of biology, then build upward — the code, what it folds into, how energy gets in, and how cells signal and defend.

About 3 hours of reading · 38 widgets

Start with Natural Selection
  1. Biology10 min

    Part 1: Natural Selection

    How three plain requirements — variation, heritability, and differential reproduction — force populations to change, why the algebra of allele frequencies makes it inevitable, and where random drift takes over from selection.

  2. Biology10 min

    Part 2: DNA Replication

    The replication fork, the antiparallel problem that forces one strand to be built backwards in pieces, and the layered error correction that drives the final error rate down to one in a billion.

  3. Biology10 min

    Part 3: From DNA to Protein

    The central dogma as information flow: transcription into messenger RNA, the triplet code and its built-in redundancy, translation at the ribosome, and why one genome can build hundreds of different cells.

  4. Biology10 min

    Part 4: Epigenetics: The Marks Above the Genes

    How chemical marks — DNA methylation and histone modifications — switch genes on and off without altering the DNA sequence, giving one genome the power to build hundreds of different cells.

  5. Biology10 min

    Part 5: CRISPR: Programmable Molecular Scissors

    How CRISPR-Cas9 uses a guide RNA to find and cut a matching DNA sequence, why the cell's own repair machinery makes the actual edit, and where the risks and hype diverge.

  6. Biology10 min

    Part 6: Heredity and Mendelian Genetics

    How Mendel's pea experiments overturned blending inheritance, why a monohybrid cross gives 3:1 and a dihybrid 9:3:3:1, and how the Punnett square is just a probability calculation over discrete alleles.

  7. Biology10 min

    Part 7: Cell Division and the Cell Cycle

    The cell cycle from G1 through the M phase, mitosis stage by stage, the checkpoints that stop a cell from dividing at the wrong time, and how their failure becomes cancer.

  8. Biology10 min

    Part 8: Stem Cells: The Body's Master Cells

    What stem cells actually are — self-renewal, differentiation, and a potency hierarchy from totipotent to unipotent — plus iPSCs, real medical uses, and the hype to ignore.

  9. Biology10 min

    Part 9: Protein Folding

    Levinthal's paradox, the hydrophobic effect that actually drives collapse, and the funnelled energy landscape that lets a protein find its native structure without ever searching for it.

  10. Biology10 min

    Part 10: Enzymes: The Catalysts That Run Life

    How enzymes accelerate biochemical reactions by lowering activation energy, why they are never used up, and why they can't change where a reaction ends.

  11. Biology11 min

    Part 11: Photosynthesis

    How a green pigment, a proton gradient, and one famously sloppy enzyme convert sunlight into the carbon in your body — and why the whole apparatus runs at about one percent efficiency.

  12. Biology10 min

    Part 12: Cellular Respiration

    How your cells release the energy stored in glucose one small step at a time, run photosynthesis's own machinery in reverse, and pay for the privilege of not catching fire.

  13. Biology10 min

    Part 13: Cell Membranes and Transport

    How a self-assembling lipid bilayer becomes a selectively permeable barrier, why diffusion and osmosis move solutes for free while pumps spend ATP to push them uphill, and how those hard-won gradients power the rest of physiology.

  14. Biology10 min

    Part 14: Osmosis: Why Water Moves on Its Own

    Osmosis is the passive diffusion of water — not solute — across a semipermeable membrane toward the more concentrated side, driven by chance and stopped only when water potential equalizes.

  15. Biology10 min

    Part 15: The Action Potential

    The voltage spike that carries information through your nervous system, from ion channels to ECG.

  16. Biology10 min

    Part 16: The Synapse: How Neurons Talk

    Why the spike can't jump the gap, how a chemical synapse relays it step by step, and why the receiving neuron sums many excitatory and inhibitory inputs before deciding to fire.

  17. Biology10 min

    Part 17: Viruses: Alive or Not?

    What a virus actually is, why it is not a small bacterium, how it hijacks a host cell to copy itself, and why antibiotics do nothing to it.

  18. Biology10 min

    Part 18: The Microbiome: Your Body's Microbial Partners

    The trillions of microbes living in and on you are mostly harmless or helpful — fermenting fiber, making vitamins, training immunity, and crowding out pathogens.

  19. Biology10 min

    Part 19: The Adaptive Immune Response

    How clonal selection, exponential expansion, and immunological memory turn a week-long illness into an infection you never notice — and how vaccines exploit the gap.