Capsules

Emotion

States combining physiological change, expressive behaviour and subjective feeling, arising in response to events that matter to the organism. What…

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Aug 5, 2026

Cell Membranes

The boundary enclosing every cell, formed from a double layer of lipid molecules with proteins embedded in it. It defines what is inside the cell,…

Archaea

A domain of single-celled organisms distinct from both bacteria and eukaryotes. Their recognition as a separate branch of life in 1977 restructured…

Lipids

A class of biological molecules grouped by not dissolving in water. They store energy, form the boundaries of every cell, and act as signalling…

Sex Determination

The mechanisms by which an organism develops as male, female or another form. The systems are far more varied than the mammalian arrangement…

Inflammation

The body's response to injury or infection, producing redness, heat, swelling and pain. It is protective and necessary, and when it persists without…

Fungi

A kingdom of organisms distinct from plants and animals, which digest their food externally and absorb it. They decompose most of the world's dead…

Antibodies

Proteins produced by the immune system that bind specifically to a target and mark it for removal. Their variety is generated at random before any…

Metabolism

The complete set of chemical reactions that sustain a living organism. It extracts energy from the environment, builds and maintains structures, and…

Bacteria

Single-celled organisms without a nucleus, present in essentially every environment on Earth, and vastly outnumbering all other forms of life. A…

Proteins

The molecules that carry out most of the work in a cell. They are built from a common set of twenty amino acids, and what each one does is determined…

Chromosomes

The structures into which the DNA of a cell is packaged. They are how an organism's genetic material is organised, divided accurately between…

The Immune System

The set of cells, tissues and molecules that defends the body against infection. It operates in two connected layers: a fast general response, and a…

The Neuron

The cell type that carries and processes signals in the nervous system. Neurons are electrically excitable, connect to one another at junctions…

Contested

Why We Sleep

Sleep is universal among animals with nervous systems, is regulated with precision, and is fatal to eliminate. What it is for remains unresolved, and…

Debunked

Preformationism

The doctrine that an organism exists fully formed in miniature within the egg or the sperm, and that development is merely the enlargement of a…

Debunked

Lysenkoism

The agricultural biology of Trofim Lysenko, adopted as official Soviet doctrine from the 1930s to the mid-1960s, which rejected genetics as a…

Debunked

Recapitulation Theory

Ernst Haeckel's claim that an embryo passes through the adult forms of its ancestors as it develops, summarised as the slogan that ontogeny…

Theory

Life History Theory

The framework that treats an organism's schedule of growth, reproduction and death as an evolved allocation of limited resources, subject to…

Proven

Chirality

The property of an object that cannot be superimposed on its mirror image, as with a left and a right hand. In chemistry it applies to molecules, and…