Biology Glossary
Every key term from biology in one place. Each card shows an icon and a short definition. Click any card with a clickable icon to open the full labeled diagram.
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abioticA non-living factor in an ecosystem (water, sunlight, temperature, soil).
active transportMoving molecules against the gradient — requires ATP energy.
adaptive traitA trait that helps an organism survive and reproduce in its environment.
allelesA version of a gene. The gene for eye color has alleles for blue, brown, and other colors.
amino acidThe building block of proteins. Amino acids link together in chains to form proteins.
anaphaseThird stage of mitosis. Chromosomes pull apart toward opposite ends.
ATPThe energy molecule — powers nearly everything cells do.
bioticA living factor in an ecosystem (plants, animals, fungi, bacteria).
carbohydratesA sugar or starch molecule — the body's quick energy source.
carriersA heterozygote for a recessive trait. Doesn't show the trait but can pass it to their children.
carrying capacityThe maximum population size an environment can support long-term.
plasma membraneThe flexible outer boundary of every cell — controls what enters and leaves.
respirationCells break down glucose with oxygen to make ATP energy.
central dogmaThe flow of genetic information in a cell: DNA → RNA → protein.
chloroplastsThe organelle in plant cells where photosynthesis happens.
chromosomesDNA wound up tightly into a compact X or rod shape. You see chromosomes when a cell is about to divide.
codominantInheritance where BOTH alleles are visible at once, not blended. Example: a roan cow has red AND white hairs visible.
codonsA group of three mRNA bases that codes for one amino acid.
commensalismA relationship where one species benefits and the other is unaffected (+/0).
heterotrophAn organism that gets energy by eating other organisms.
convergentUnrelated species evolving similar traits because they live in similar environments.
crossoverWhen paired chromosomes swap pieces during meiosis, increasing variation.
decomposerAn organism that breaks down dead things and recycles nutrients.
diffuseThe spreading of particles from where there are many to where there are few.
2nA cell with the full set of chromosomes (2n). Body cells are diploid.
DNAThe molecule that carries the genetic instructions for life. Shaped like a twisted ladder.
dominant alleleAn allele that hides the other when both are present. Written with a capital letter, like B.
double-helix shapeThe twisted-ladder shape of DNA. Two strands wound around each other.
ecosystemAll the living and non-living things in one area, working together.
enzymesA protein that speeds up a chemical reaction in the body.
eukaryoticA cell with a nucleus and membrane-bound organelles inside.
biological evolutionHow species change over time through inherited traits and natural selection.
negative feedbackA system that detects change and responds to correct or amplify it.
gametesA sex cell — an egg or a sperm. Has half the normal chromosomes.
genesA section of DNA that holds the instructions to build one protein.
genotypesThe two alleles a person has for a trait, written like Bb, BB, or bb.
glucoseA simple sugar — the building block of carbohydrates.
nA cell with half the chromosomes (n). Eggs and sperm are haploid.
heterozygoteThe two alleles for a trait are different — like Bb. "Hetero-" means different.
homeostasisThe body's ability to keep internal conditions stable.
homologous structuresStructures in different species that share the same origin but may have different functions.
homozygoteBoth alleles for a trait are the same — either BB or bb. "Homo-" means same.
incomplete dominantInheritance where the two alleles blend into a new in-between trait. Example: red flower × white flower → pink flowers.
lipidsA fat or oil — stores energy and makes up cell membranes.
meiotic divisionCell division that makes 4 sex cells (eggs or sperm) with half the DNA.
metaphaseSecond stage of mitosis. Chromosomes line up in the middle.
mitochondrionThe organelle that makes ATP — the cell's energy source.
mitotic divisionCell division — one cell becomes two identical cells.
mRNAMessenger RNA — a single-stranded copy of a gene that carries the message from DNA to the ribosome.
mutationsA change in the DNA sequence that can create a new allele or alter a protein.
mutualismA relationship where both species benefit (+/+).
survival of the fittestProcess where organisms with helpful traits survive and reproduce more.
nitrogenous basesThe "letter" part of a nucleotide. The four bases in DNA are A, T, C, and G.
nucleotidesThe building block of DNA. Made of a phosphate, a sugar, and a base.
nucleiThe control center of a eukaryotic cell — holds the DNA.
organellesA small part inside a cell that does a specific job.
osmosisThe diffusion of water across a membrane — high to low.
parasitismA relationship where one species benefits and the other is harmed (+/−).
pedigree chartA family-tree diagram showing which family members have a trait. Squares = males, circles = females, filled-in = has the trait.
phenotypesThe trait you can see — like brown eyes, blue eyes, pink flowers, or type-A blood.
photosynthesisPlants use light, CO2, and water to make glucose and oxygen.
populationAll the organisms of one species living in one area at one time.
autotrophAn organism that makes its own food from sunlight (like a plant).
prokaryoticA cell with no nucleus — its DNA floats freely inside.
prophaseFirst stage of mitosis. Chromosomes condense and become visible.
proteinsA large molecule made of amino acids — does many jobs in cells.
Punnett squareA grid that shows all the possible offspring genotypes when two parents are crossed.
recessive alleleAn allele that's hidden when paired with a dominant one. Written with a lowercase letter, like b. Only shows when both alleles are recessive.
DNA replicationThe process where one DNA molecule is copied to make two identical DNA molecules.
ribosomesThe cell structure where proteins are built. The ribosome reads mRNA and links amino acids together.
X-linkedA trait carried on the X chromosome. Recessive sex-linked traits show up more in males because males have only one X.
speciationThe formation of new species when populations become separated and evolve differently.
telophaseFourth stage of mitosis. Two new nuclei form and the cell divides.
transcribeThe first step of protein synthesis: a DNA gene is copied into a strand of mRNA.
translateThe second step of protein synthesis: mRNA is read at the ribosome and used to build a protein.
tRNATransfer RNA — a small RNA molecule that carries an amino acid to the ribosome during translation.