Biology Glossary

A working glossary of biology vocabulary. Each term gets a one-sentence working definition (enough to keep reading) and, where we cover it in depth, a link to the article that goes further.

This is a reference. Skim it, search it (Ctrl+F or Cmd+F is your friend), or use it as a study aid before a quiz.

A

Adaptation — A trait that has evolved because it improves an organism's survival or reproduction in its environment. Adaptations are the result of natural selection acting on heritable variation.

Allele — One of two or more alternative forms of a gene. You inherit one allele from each parent for most genes.

Anatomy — The study of biological structure — what an organism is made of and what its parts look like. (Compare with physiology.) See: How the Human Body Works.

Antibody — A protein produced by the immune system that recognizes and binds to a specific foreign molecule (usually part of a pathogen).

Archaea — A domain of single-celled microorganisms distinct from bacteria. Often found in extreme environments. See: The Microbial World.

B

Bacteria — Single-celled microorganisms. The most numerous kind of cellular life on Earth. Some cause disease; most are harmless or beneficial. See: The Microbial World.

Biodiversity — The variety of life — the number of different species in a habitat, plus the genetic variation within them. See: Biodiversity Hotspots.

Biome — A large geographic region defined by its climate and dominant vegetation — for example, tropical rainforest, temperate grassland, tundra, coral reef.

Biotechnology — The application of biological science to industry, medicine, and agriculture. See: Genetic Engineering.

C

Carbon Cycle — The continual movement of carbon between the atmosphere, the oceans, living things, and the geosphere. Photosynthesis pulls carbon out of the atmosphere; respiration and decomposition put it back. See: The Role of Biology in Combating Climate Change.

Cell — The smallest unit of life. Every known living organism is made of one or more cells.

Cell Membrane — The lipid bilayer that separates the inside of a cell from the outside world and controls what passes in and out.

Chlorophyll — The green pigment in plants and many algae that absorbs light energy for photosynthesis. See: The Secret Life of Plants.

Chromosome — A long, organized package of DNA found inside the nucleus of a cell. Humans have 23 pairs (46 total).

Climate Change — Long-term shifts in temperature and weather patterns. The current episode is being driven primarily by human emission of greenhouse gases. See: The Role of Biology in Combating Climate Change.

CRISPR — A genome-editing technology adapted from a bacterial defense system. Allows precise cuts at specific DNA sequences. See: CRISPR: Revolutionizing the Future of Medicine and Genetics.

D

DNA (Deoxyribonucleic Acid) — The molecule that carries the genetic instructions for the development and functioning of all known living organisms. Made of four nucleotide bases (A, T, G, C) in a double-helix structure. See: Top 10 Fascinating Facts About Human DNA.

Decomposer — An organism (usually a bacterium or fungus) that breaks down dead organic matter, returning nutrients to the ecosystem.

Differentiation — The process by which a relatively unspecialized cell becomes a specialized one (a nerve cell, a muscle cell, etc.).

E

Ecosystem — A community of living organisms together with the non-living components of their environment, interacting as a system. See: Ecology in Action: How Ecosystems Work.

Endocrine System — The collection of glands that produce hormones to regulate body functions like growth, metabolism, and mood.

Enzyme — A protein that catalyzes a specific chemical reaction. Most of cellular metabolism is run by enzymes.

Eukaryote — A cell with a true nucleus and other membrane-bound organelles. All animals, plants, fungi, and protists are eukaryotes.

Evolution — The change in heritable characteristics of biological populations over successive generations. Driven by mechanisms including natural selection, mutation, and genetic drift. See: The Evolution of Life.

G

Gene — A unit of heredity. A specific sequence of DNA that codes for a particular protein or has a regulatory function.

Gene Editing — Modifying the DNA sequence of a living organism. CRISPR is the best-known modern gene-editing tool. See: CRISPR.

Genome — The complete set of genetic material in an organism. The human genome contains about 3 billion DNA base pairs.

Genotype — An organism's complete set of genes; the genetic version of "what the instructions say." Compare with phenotype.

H

Habitat — The natural environment in which an organism lives.

Homeostasis — The maintenance of stable internal conditions despite changes in the external environment — for example, keeping body temperature near 37°C.

Hormone — A chemical messenger produced by an endocrine gland and transported through the bloodstream to target tissues.

I

Immune System — The body's network of cells and proteins that defends against infection. See: How the Human Body Works.

Inheritance — The passing of genetic information from parent to offspring.

M

Microbiome — The community of microorganisms that live in a particular environment — for example, the human gut microbiome.

Mitosis — The process by which a single cell divides into two genetically identical daughter cells. The basis of body growth and tissue repair.

Mutation — A change in the DNA sequence. Mutations are the raw material of evolution; most are neutral, some are harmful, and a small number are beneficial.

N

Natural Selection — The process by which heritable traits that improve survival and reproduction become more common in a population over generations. The primary mechanism of evolution.

Nucleus — The membrane-bound structure inside a eukaryotic cell that contains the chromosomes.

O

Organ — A group of tissues working together to perform a specific function (heart, kidney, brain, etc.).

Organism — An individual living thing — a single cell, a plant, an animal, a fungus.

P

Pathogen — An organism that causes disease. Includes some bacteria, viruses, fungi, and parasites.

Phenotype — An organism's observable characteristics — height, eye color, behavior — the result of its genotype interacting with its environment.

Photosynthesis — The process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose, releasing oxygen as a byproduct. See: The Secret Life of Plants.

Physiology — The study of biological function — how organs and cells actually work. (Compare with anatomy.)

Prokaryote — A cell without a nucleus. Bacteria and archaea are prokaryotes. They were the only kind of life on Earth for about 2 billion years.

Protein — A large molecule made of chains of amino acids. Proteins do most of the work inside cells — catalyzing reactions (as enzymes), providing structure, sending signals, and transporting molecules.

R

Respiration (cellular) — The set of metabolic reactions inside a cell that convert glucose and oxygen into energy (ATP), releasing carbon dioxide and water.

Ribosome — The cellular machine that reads messenger RNA and builds proteins.

RNA (Ribonucleic Acid) — A nucleic acid similar to DNA but usually single-stranded. Several types of RNA play distinct roles in protein synthesis; some viruses use RNA as their genetic material instead of DNA.

S

Species — A group of living organisms that can interbreed and produce fertile offspring. The basic unit of biological classification.

Stem Cell — An undifferentiated cell that can divide to produce more stem cells AND can differentiate into specialized cell types.

Symbiosis — A close, long-term biological relationship between two species. Includes mutualism (both benefit), commensalism (one benefits, the other is unaffected), and parasitism (one benefits at the other's expense).

T

Taxonomy — The science of naming, classifying, and organizing living things into a hierarchy of groups (domain, kingdom, phylum, class, order, family, genus, species).

Tissue — A group of similar cells working together to perform a function (muscle tissue, nervous tissue, etc.).

V

Virus — A small infectious agent that replicates only inside the cells of a host organism. Not technically a cell, and arguably not even alive. See: Understanding Viruses.

See Also

• What Is Biology? — Big-picture orientation to the field.
• Branches of Biology — How biology divides itself into specialties.
• Biology resources hub — Every Biology Contest article, organized by subtopic.