Biology
Life’s diversity
Domains, a phylogeny sketch, homology versus analogy, and binomial names.
Basics
Three domains
Cellular life is split into Bacteria, Archaea, and Eukarya. Bacteria and archaea lack a nuclear envelope; eukaryotes have a nucleus and usually mitochondria. Archaea are not only extremophiles — they live in oceans, soils, and human bodies. Plants, animals, and fungi are kingdoms inside Eukarya. Viruses are not cells, so many schemes leave them outside the three domains. Sequence trees often recover the same three deep branches.
Phylogeny sketch
A phylogeny draws history as branches from common ancestors. Tips are living taxa; nodes are inferred ancestors. Branch length may mean time or amount of change. A clade (monophyletic group) holds an ancestor and all its descendants. Reptiles without birds are paraphyletic. Trees are hypotheses — new data can move the forks.
Homology and analogy
Homology is inheritance from a common ancestor (forelimb bones in humans and bats). Analogy is convergent similarity of use (bird and insect wings). Classification trusts homology more. Molecules too: copies of the same gene versus different genes with similar jobs. Do not declare kinship from looks alone.
Binomial names
Linnaean binomials are genus + specific epithet, e.g. Homo sapiens. Capitalise the genus, lower-case the epithet, and italicise in print. Many common names can map to one scientific name. Subspecies may add a third word. Codes of nomenclature (animals, plants, bacteria differ) settle priority.
Formulas
Nested ranks (sketch)
Broader above, narrower below.
Binomial form
Genus + epithet; author citation optional after.
Key table
| LUCA | last universal common ancestor — cellular and genetic backbone |
|---|---|
| Convergence | similar ecology makes similar shapes; keep apart from homology |
| Priority | the earliest validly published name usually wins |
In this field
The cell
Prokaryotes vs eukaryotes, organelles, membranes.
Genetics and molecular biology
DNA, transcription/translation, Mendel, meiosis.
Metabolism
Photosynthesis, respiration, ATP, enzymes.
Evolution and ecology
Natural selection, phylogeny, trophic levels, cycles.
Human physiology basics
Homeostasis, circulation, nerves, immunity.
Plants and development
Plant tissues, hormones, developmental stages.
Immunity and microbes
Pathogens, innate and adaptive immunity, antibiotics and vaccines.
Nervous and endocrine systems
Neurons, synapses, hormones, and homeostasis — fast electrical and slower chemical signals.
Molecular lab sketch
Restriction enzymes, electrophoresis, PCR, and sequencing — a short principle sketch.
Population ecology
Exponential and logistic growth, carrying capacity, life history, predator–prey sketch.
Biological macromolecules
Carbohydrates, lipids, proteins, and nucleic acids — structure and role sketches.