QCAA Biology EA key terms

The principle that all living things are made of one or more cells, that the cell is the basic unit of life, and that new cells arise only from existing cells by division.

A single-celled organism lacking a membrane-bound nucleus and other membrane-bound organelles, with genetic material existing as a circular chromosome in the cytoplasm, such as bacteria and archaea.

An organism whose cells contain a nucleus enclosing the genetic material and other membrane-bound organelles, including protists, fungi, plants and animals.

A specialised structure within a cell that performs a particular function, such as a mitochondrion or chloroplast, often enclosed by its own membrane.

A thin, selectively permeable barrier of phospholipids and proteins surrounding the cytoplasm that controls which substances enter and leave the cell.

A double-membraned organelle where aerobic cellular respiration occurs, producing most of the cell's ATP from glucose and oxygen.

A membrane-bound organelle containing chlorophyll and stacked thylakoid membranes where photosynthesis converts light energy into chemical energy stored in glucose.

A small structure, free in the cytoplasm or attached to rough endoplasmic reticulum, that assembles amino acids into proteins by translating messenger RNA.

The net passive movement of particles from a region of higher concentration to a region of lower concentration, driven by random molecular motion.

The passive movement of water molecules across a selectively permeable membrane from a region of higher water potential to a region of lower water potential.

A type of nuclear division producing two genetically identical daughter cells with the same chromosome number as the parent, used for growth, repair and asexual reproduction.

The ordered sequence of stages a cell passes through between successive divisions, including interphase growth and DNA replication followed by mitosis and cytokinesis.

Programmed cell death in which a cell dismantles itself in a controlled way, important in development and in removing damaged cells.

The maintenance of a relatively stable internal environment within narrow limits despite changes in the external environment, achieved through coordinated physiological control systems.

A control mechanism in which a detected deviation from a set point triggers a response that reduces that deviation, returning the internal environment towards its normal value.

The target value around which a physiological variable such as temperature or blood glucose concentration is regulated by homeostatic control systems.

The control of body temperature through mechanisms such as sweating, vasodilation, shivering and vasoconstriction, balancing heat gain against heat loss.

The control of water and dissolved solute balance in body fluids, achieved largely by the kidneys adjusting water reabsorption and solute excretion.

The microscopic functional unit of the kidney where blood is filtered and useful substances are reabsorbed, producing urine.

A chemical messenger secreted by an endocrine gland into the bloodstream that acts on target cells bearing specific receptors to alter their activity.

A protein molecule, on a cell membrane or inside a cell, that binds specifically to a signalling molecule and triggers a response in the target cell.

A disease-causing agent such as a bacterium, virus, fungus or parasite that invades the body and can trigger an immune response.

A Y-shaped protein produced by plasma cells that binds specifically to an antigen, marking the pathogen for destruction or neutralising it.

The coordinated defence mounted by the body against a pathogen, involving barriers, inflammation, phagocytes and specific lymphocytes.

A length of DNA that carries the instructions for making a particular protein or functional RNA molecule, and is inherited from parent to offspring.

One of the alternative versions of a gene that can occupy the same position on a chromosome, producing variation in a trait.

The particular combination of alleles an organism carries for a gene or set of genes, which together with the environment determines the phenotype.

The observable characteristics of an organism resulting from the interaction between its genotype and the environment.

A reduction division producing four genetically varied haploid gametes, involving two successive divisions and crossing over and independent assortment of chromosomes.

The exchange of corresponding segments of DNA between homologous chromosomes during prophase I of meiosis, generating new allele combinations in gametes.

A family tree diagram using standard symbols to show the inheritance of a trait across generations, used to infer modes of inheritance.

A permanent change in the base sequence of DNA that may alter the protein produced and can be inherited if it occurs in gametes.

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

An inherited structural, physiological or behavioural feature that improves an organism's chance of survival and reproduction in its environment.

The variety of life in an area, measured as variation within species, between species and of ecosystems.

A community of interacting organisms together with the non-living components of their environment, through which energy and matter flow.

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

A species whose influence on its community is disproportionately large relative to its abundance, so its removal causes major changes to the ecosystem.

The proportion of all copies of a gene in a population that are a particular allele, used to describe and track genetic change over time.