BIOLOGY DEFINITIONS FOR CIE AS AND A LEVEL

Flashcards covering key biology definitions across cell structure, biomolecules, membranes, nucleic acids, transport, immunity, energy, plants, disease, genetics, biodiversity, and genetic technology.

Magnification

The number of times greater the image is than the actual object.

Resolution

The ability to distinguish between two objects that are very close together; higher resolution gives more detail.

Macromolecule

A large biological molecule; three main types in living organisms: polysaccharides, proteins (polypeptides) and nucleic acids (polynucleotides).

Polymer

A molecule made up of many repeating subunits that are similar or identical to each other.

Monomer

A simple molecule used as a basic building block for a polymer; usually joined by condensation reactions. Examples: monosaccharides, amino acids and nucleotides.

Monosaccharide

Single-sugar molecule. Examples include glucose, galactose and fructose; classified by the number of carbon atoms (Trioses, Pentoses, Hexoses).

Trioses

Three-carbon monosaccharides.

Pentose

Five-carbon monosaccharide.

Hexose

Six-carbon monosaccharide.

Disaccharide

A sugar formed by two monosaccharides joined by a glycosidic bond (e.g., maltose, sucrose, lactose).

Polysaccharide

A polymer whose subunits are monosaccharides joined by glycosidic bonds; examples include starch, glycogen and cellulose.

Primary structure

The sequence of amino acids in a polypeptide or protein, held together by peptide bonds.

Secondary structure

Regular coiling or folding of the amino acid chain; examples include α-helix and β-pleated sheet.

Tertiary structure

The 3D compact folding of a protein molecule.

Quaternary structure

The 3D arrangement of two or more polypeptides or of a polypeptide and a non-protein component (e.g., haem in a protein).

Oligosaccharide

A short chain of sugar molecules.

Glycoprotein

A protein with carbohydrate attached covalently.

Glycolipid

A lipid with carbohydrate attached.

Peripheral protein

A protein that is attached to the membrane surface rather than embedded in the bilayer.

Integral

An integral protein is a membrane protein embedded within the phospholipid bilayer.

Hydrophobic proteins

Proteins with hydrophobic regions, often spanning the membrane.

Alpha helix

A common helical secondary structure of proteins.

Cholesterol

A sterol molecule in membranes that modulates fluidity.

Phospholipid

A lipid with a hydrophilic phosphate-containing head and a hydrophobic tail.

Diffusion

Net movement of molecules from a region of higher concentration to lower concentration down a gradient due to random motion.

Facilitated diffusion

Diffusion of a substance through transport proteins in a cell membrane, via hydrophilic channels.

Osmosis

Net movement of water from higher water potential to lower water potential through a partially permeable membrane by diffusion.

Active transport

Movement of molecules or ions through transport proteins against their concentration gradient, using energy from ATP.

Endocytosis

Bulk movement of liquids (pinocytosis) or solids (phagocytosis) into a cell via membrane invagination; active process requiring ATP.

Exocytosis

Bulk movement of liquids or solids out of a cell via vesicle fusion with the membrane; active process requiring ATP.

Gene

A length of DNA that codes for a particular protein or polypeptide.

Gene mutation

A change in the base sequence of part of the DNA molecule that may alter the polypeptide.

Codon

A three-base sequence on mRNA that codes for a specific amino acid.

Anticodon

A three-base sequence on tRNA that pairs with the mRNA codon.

tRNA

Transfer RNA; carries amino acids to the ribosome during translation.

mRNA

Messenger RNA; carries the genetic code from DNA to the ribosome; contains codons.

Ribosome

Ribosomal RNA–protein complex where protein synthesis occurs; composed of ribosomal subunits.

Amino acids

Building blocks of proteins; linked by peptide bonds to form polypeptides.

Ribosomal subunits

The two parts of a ribosome that come together during protein synthesis.

Plasmodesma

Cytoplasmic channels through plant cell walls that connect adjacent plant cells.

Apoplastic pathway

Transport through the cell walls and spaces outside the plasma membrane.

Symplastic pathway

Transport through the cytoplasm of plant cells linked by plasmodesmata.

Transpiration

Loss of water vapour from a plant to its environment by diffusion down a water potential gradient, mainly via stomata.

Disease

An illness or disorder of the body or mind; associated with signs and symptoms.

Infectious disease

A disease caused by pathogens; also called communicable diseases.

Non-infectious disease

Diseases not caused by pathogens; includes genetic, cardiovascular, deficiency and mental diseases.

Antigen

A substance foreign to the body that stimulates an immune response.

Antibody

A glycoprotein (immunoglobulin) produced by plasma cells; binds specifically to an antigen.

Immune response

The series of responses involving lymphocytes and phagocytes to a foreign antigen.

Non-self

A substance or cell recognised as foreign by the immune system.

Self

Substances produced by the body that are not recognised as foreign by the immune system.

Active immunity

Immunity gained when an antigen enters the body, triggering an immune response and antibody production.

Passive immunity

Immunity gained without an immune response; antibodies are injected or transferred from mother.

Natural immunity

Immunity gained by infection (active) or by receiving antibodies from the mother (passive).

Artificial immunity

Immunity gained by vaccination (active) or by injecting antibodies (passive).

Vaccination

Giving a vaccine containing antigens to confer artificial active immunity.

Organic molecule

A compound containing carbon and hydrogen.

Respiratory Quotient (RQ)

The ratio of CO2 produced to O2 consumed during respiration (RQ = CO2/O2).

Limiting factor

The factor that limits the rate of a process when more than one factor is involved; the rate is determined by the factor at its lowest value.

Homeostasis

Maintenance of a relatively constant internal environment amid external changes.

Negative feedback

A process where a change in a parameter triggers responses that move it back toward normal.

Homologous chromosomes

A pair of chromosomes in a diploid cell with the same structure and genes at the same loci; pair to form a bivalent during meiosis.

Allele

A particular variant of a gene.

Locus

The position of a gene on a chromosome; the same gene is located at the same locus.

Diploid

Cell possessing two complete sets of chromosomes (2n).

Haploid

Cell possessing one complete set of chromosomes (n).

Genotype

The alleles possessed by an organism.

Homozygous

Having two identical alleles of a gene.

Heterozygous

Having two different alleles of a gene.

Phenotype

The observable characteristics of an organism, resulting from genotype and environment.

Dominant allele

An allele whose effect on the phenotype is expressed in a heterozygote as well as a homozygote.

Recessive allele

An allele expressed only when no dominant allele is present.

Codominant alleles

Alleles that both have an effect on the phenotype in a heterozygous organism.

F1 generation

Offspring from a cross between a homozygous dominant and a homozygous recessive organism.

F2 generation

Offspring from a cross between two F1 (heterozygous) organisms.

Test cross

A cross between an organism showing a dominant phenotype and a homozygous recessive to deduce the genotype.

Structural genes

Genes that code for the proteins required by a cell for structure or metabolism.

Regulatory genes

Genes that control the expression of other genes.

Repressor protein

A protein that can block synthesis of a repressible enzyme by binding to the operator site.

Operator site

A DNA sequence to which regulatory proteins bind to control gene expression.

Inducible enzyme

An enzyme synthesized only when its substrate is present.

Repressible enzyme

An enzyme whose synthesis is repressed unless its substrate is present.

Recombinant DNA

DNA formed by joining pieces from two or more different sources.

Bioinformatics

The collection, processing and analysis of biological information using computer software.

Species

A group of organisms that can breed to produce fertile offspring and are reproductively isolated from others.

Ecosystem

A relatively self-contained, interacting community of organisms and the environment.

Niche

The role of an organism in its ecosystem.

Recombinant DNA (duplicate)

DNA formed by joining pieces from two or more sources.

Bioinformatics (duplicate)

Collection and analysis of biological data using computer software.