ILTS Science: Biology (239) key terms

A thin, flexible barrier of phospholipids and proteins surrounding every cell that controls which substances enter and leave, and helps cells communicate and stick to neighbors.

Two layers of phospholipid molecules arranged with water-fearing tails inward and water-loving heads outward, forming the basic structural fabric of all cell membranes.

The property of a membrane that lets some substances pass through easily while blocking or limiting others, largely due to lipid solubility, size, charge, and transport proteins.

The net movement of water across a selectively permeable membrane from an area of higher water concentration (lower solute concentration) to one of lower water concentration.

A solution with a higher solute concentration than the cell placed in it, causing water to leave the cell and leading to shrinkage or shriveling.

Passive movement of molecules across a membrane through channel or carrier proteins, always down a concentration gradient and requiring no cellular energy input.

Movement of substances across a membrane against their concentration gradient using energy, typically from ATP hydrolysis, and often carried out by pump proteins such as the sodium-potassium pump.

A difference in the amount of a dissolved substance between two regions, which drives diffusion and is the basis for passive transport and nerve impulse generation.

A double-membraned organelle where aerobic cellular respiration occurs, producing most of a eukaryotic cell's ATP through the electron transport chain and chemiosmosis.

A plant and algal organelle containing chlorophyll and thylakoid membranes where photosynthesis converts light energy into chemical energy stored in sugars.

A complex of RNA and protein, free in the cytoplasm or attached to rough endoplasmic reticulum, that assembles amino acids into polypeptides during translation.

A network of membrane-bound sacs and tubules; rough ER studded with ribosomes modifies and folds proteins, while smooth ER synthesizes lipids and detoxifies substances.

A stack of flattened membrane sacs that modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum for transport or secretion.

A membrane-bound vesicle containing digestive enzymes that breaks down worn-out organelles, food particles, and foreign material inside eukaryotic cells.

A single-celled organism lacking a membrane-bound nucleus and membrane-bound organelles, including bacteria and archaea, with circular DNA in a nucleoid region.

An organism whose cells contain a true nucleus enclosing the chromosomes and other membrane-bound organelles; includes protists, fungi, plants, and animals.

Nuclear division producing two genetically identical daughter nuclei with the same chromosome number as the parent cell, used for growth, repair, and asexual reproduction.

Two successive nuclear divisions that halve the chromosome number and produce four genetically varied haploid cells, forming gametes or spores in sexually reproducing organisms.

Exchange of corresponding chromosome segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis, increasing genetic variation in offspring.

A pair of chromosomes, one inherited from each parent, that carry genes for the same traits at the same loci and pair during meiosis.

Having one complete set of chromosomes, symbolized n, as in gametes and spores produced by meiosis; the opposite of diploid.

The ordered sequence of interphase growth and DNA replication followed by mitosis and cytokinesis, through which a cell duplicates and divides.

One of two or more alternative forms of a gene at a given locus, which may produce different versions of a trait such as flower color.

The particular combination of alleles an organism carries for a gene or set of genes, such as homozygous dominant, heterozygous, or homozygous recessive.

The observable physical or biochemical characteristics of an organism, resulting from genotype interacting with environmental influences.

A grid diagram used to predict the possible genotypes and their expected proportions among offspring of a cross between parents of known genotypes.

The synthesis of an RNA molecule from a DNA template, catalyzed by RNA polymerase, occurring in the nucleus of eukaryotes and cytoplasm of prokaryotes.

The process at ribosomes in which messenger RNA codons are read and matched by transfer RNA to assemble amino acids into a polypeptide chain.

A sequence of three nucleotides in messenger RNA that specifies one amino acid or a stop signal during protein synthesis.

A heritable change in the nucleotide sequence of DNA, such as substitution, insertion, or deletion, which may alter protein structure or gene regulation.

The process by which individuals with heritable traits better suited to their environment survive and reproduce more successfully, increasing those traits in later generations.

An inherited trait or characteristic that improves an organism's ability to survive and reproduce in its particular environment, arising over generations through natural selection.

Random change in allele frequencies in a population, especially pronounced in small populations, caused by chance events rather than selection.

Movement of alleles between populations through migration and interbreeding, which tends to reduce genetic differences among populations.

The evolutionary formation of new, reproductively isolated species from a common ancestral population, often following geographic or genetic separation.

A feeding position in a food chain or web, such as producer, primary consumer, or secondary consumer, defined by number of energy-transfer steps from the sun.

The maximum population size of a species that a given environment can sustain indefinitely, given available food, water, habitat, and other limiting resources.

The maintenance of a relatively stable internal environment in an organism, achieved through feedback mechanisms that regulate temperature, pH, water, and solute balance.