Glossary of technical terms
The spellings and explanations in this glossary will be used in examinations, but it is not to be taken as the only possible definition. The intention is to provide clear usable definitions for all words that are referred to in the assessment statements, by "define….. It should also reduce ambiguity where more than one word is used for the same concept, structure, etc..
Whether a student can recall and understand a definition may be determined in several ways including multiple choice questions, short-answer and extended response questions.
Absorption
The taking in of chemical substances through cell membranes or layers of cells.
Acrosome reaction
The release of hyaluronidase when the sperm cell membrane fuses with the acrosome (the specialised penetrating vesicle at the top of the spermatozoon). The enzyme dissolves the zona pellucida leading to fusion of sperm head and ovum.
Action potential
The localised reversal and then restoration of electrical potential between the inside and outside of a neuron as the impulse passes along it.
Active immunity
Immunity due to production of antibodies by the organism itself after the body’s defence mechanisms have been stimulated by invasion of foreign microorganisms.
Active site
The site on surface of enzyme to which substrate or substrates bind.
Allele
One specific form of a gene, differing from other alleles by one or a few bases only and occupying, the same gene locus as other alleles of the gene.
Antibody
A globular protein that recognises an antigen.
Antigen
A molecule recognised as foreign by the immune system.
Artificial immunity
Immunity due to inoculation with vaccine.
Autosome
A chromosome that is not a sex chromosome
Autotroph
An organism that produces organic master from inorganic raw materials and an external energy source.
Balanced diet
A diet that provides all nutrients in the necessary proportions.
Biomass
The total mass of organic master in organisms or ecosystems. Water is not organic master and so is not included. (The term Standing Crop which is synonymous will not be used).
Carrier
An individual that has a recessive allele of a gene that does not have an effect on the phenotype.
Carrying capacity
The maximum number of a species that can be sustainably supported by the environment.
Centimorgan (a unit of map distance)
The distance between two loci that, will give, on average, one crossover in 100 gametes.
Chiasma
The points at which homologous chromosomes remain in contact as chromatids move apart during Prophase I of meiosis or a cross-shaped structure formed by crossing over between chromosomes or two chromatids.
Classical Conditioning
The modification of behaviour in an animal as a result of detection of correlations between external events.
Clone
A group of organisms of identical genotype. OR A group of cells descended from a single parent cell.
Codominant alleles
Alleles which have a partial effect on the phenotype when present in heterozygotes but a greater effect in homozygotes. (Note: the terms incomplete and partial are no longer used).
Cohesion
The attraction between molecules of a liquid resulting from intermolecular forces.
Community
A group of populations living and interacting with each other in a habitat.
Competitive Exclusion
The elimination or one species from a communit3, by, another species with the same requirements.
Degeneracy
Having more than one base triplet to code for one amino acid.
Denaturation
A structural change in a protein (or nucleic acid) that results in a loss (temporary or permanent) of its biological properties.
Detritivore
An organism that ingests dead organic matter.
Diffusion
The passive movement of particles from a region of higher concentration to a region of lower concentration.
Dominant allele
An allele which has the same effect on the phenotype whether ¡t ¡present in the homozygous or heterozygous state.
Ecology
The study of relationships between living organisms and between them and their environment.
Ecosphere
All of the ecosystems on the Earth
Ecosystem
A community and its abiotic environment.
Endergonic
A reaction that involves the absorption of energy.
Enzyme
A globular protein functioning, as a biological catalyst.
Excretion
The removal from an organism of the toxic waste products of metabolism.
Exergonic
A reaction that involves the release of energy.
Exon
Any part of the DNA sequence giving rise to the translated polypeptide sequence.
F1 hybrid vigour
Vigour due to high levels of heterozygosity.
Fertilisation
The fusion of male and female gametes.
Fitness
The physical condition of the body which suits ¡t to the particular exercise which it performs.
Gene
An heritable factor that controls a specific characteristic, consisting of a length of DNA occupying a position on a chromosome known as a locus.
Gene mutation
A change in the base sequence of a gene.
Genetic screening
Testing a population for the presence or absence of a gene.
Genome
The total genetic material of an organelle, cell or organism.
Genotype
The alleles possessed by an organism.
Gross production
The amount of organic matter produced by photosynthesis in plants.
Habitat
The environment in which a species normally lives OR The location of a living organism.
Half- life
The time during which the radioactivity falls to half its original level.
Hardy- Weinberg Principle
If the two alleles A and a are segregating at a locus, and each has frequency of p and q respectively, then the frequencies of the genotypes AA, Aa and aa are p2, 2pp, and q2 respectively.
Harvestable dry Biomass
The dry biomass of the part of the plant of commercial value (e.g., for cereal crops the dry biomass of the grains only).
Heterotroph
An organism that obtains energy and organic matter from other organisms.
Heterozygous
Having two different alleles of a gene.
Homologous
Chromosomes with the same gene loci in the same sequence which are capable of pairing up to form bivalents during the first prophase of meiosis.
Homozygous
Having the two identical alleles of a gene
Imprinting
An attachment to an object encountered during a short period after birth, usually a parent
Inbreeding
Reproduction involving fusion of gametes produced by genetically related individuals.
Innate behaviour
Behaviour which normally occurs in all members of a species despite natural variation in environmental influences.
Insight learning
A form of intelligent activity and a function of cognitive effort, which contrasts with more passive trial and error mode of learning.
Interphase
The period between one division of the nucleus of a cell and the next division.
Interspecific Hybridisation
Sexual reproduction between members of different species.
Intron
A part of the DNA sequence which is transcribed but is not translated.It is usually spliced out during RNA processing.
Kinesis
The movement (as opposed to growth) of an organism or a cell in response to a stimulus such that rate depends on intensity but not direction of the stimulus.
Leaf area index
The ratio between the total area of leaves of a plant crop and the area of soil available to it.
Limiting factor
Variable factors which control the rate of a process when nearer their minimum than other factors.
Linkage group
A group of genes whose loci are on the same chromosome.
Locus
The particular position on homologous chromosomes of a gene.
Malnutrition
The result of feeding on a diet that is not balanced.
Mean
The "average" value obtained by dividing the total of a set of values by the number of values.
Median
The central value in a set of observations arranged in order (i.e., the value which divides the ordered set into 2 equal parts).
Meiosis
Nuclear division that produce two nuclei each genetically identical to each other and to the original parent nucleus.
Mitosis
Nuclear division that produces two nuclei each genetically identical to each other and to the original parent nucleus.
Mode
The most frequent value in a set of observations.
Mutualism
An interaction between individuals of different specie that live together (in close proximity) and by which both benefit and neither suffer. (The tem symbiosis will not be used).
Natural immunity
Immunity due to infection.
Negative feedback
The control of a process by the results or effects of the process in such a way that an increase or decrease in the results or effects is always reversed.
Net assimilation rate
The net increase in plant biomass per unit leaf area per unit time. (NAR)
NAR = increase in biomass per unit time
leaf area
Net production
The part of gross production that is not used in plant respiration.
Niche
A species’ share of a habitat and the resources in it. An organism’s ecological niche depends not only on where it lives but on what it does. The part of the habitat which a species can inhabit in the absence of competitors and predators is the fundamental niche. The part it actually occupies is its realised niche.
Nucleosome
A packing unit of eukaryotic chromosomes with DNA wound around a histone core.
Nutrient
A substance needed in the diet of an organism.
Operant conditioning
A learning procedure in which a reinforcement follows a particular response on a proportion of occasions.
Organ
A group of at least two tissue types combined to carry out a function together (eg., plant root, animal kidney).
Organic
Compounds containing carbon that are found in living organisms (except hydrogen carbonates, carbonates and oxides of carbon).
Organ system
An integrated group of organs with a common (shared) function (eg., vascular system, endocrine system).
Osmoregulation
The control of the osmotic and water potential in a cell or inside a living organism.
Outbreeding
Reproduction involving fusion of gametes produced by genetically unrelated individuals.
Partial pressure
The pressure exerted by each component in a mixture. The pressure of a gas in a mixture is the same as it would exert if it occupied the same volume alone at the same temperature (Dalton’s Law).
Passive immunity
Immunity due to acquisition of antibodies from another organism in which active immunity has been stimulated including via the placenta or in colostrum.
Pathogen
An organism causing disease.
Phenotype
All the characteristics of an organism.
Phosphorylation
The transfer of a phosphate group by a phosphatase
Plan diagram
Showing the outline of areas of each tissue but showing no detail of cells.
Pollination
The transfer of pollen from the another to the stigma.
Polygenic inheritance
A characteristic controlled by more than one gene.
Polyploidy
Having more than two haploid sets of chromosomes.
Population
A group of organisms of the same species living in the same area at the same time and capable of interbreeding.
Random sample
A method to ensure that every individual in a population has an equal chance of being observed.
Recessive allele
An allele which only has an effect on the phenotype when present in homozygous state.
Recombination
The reassortment of genes or characters into different combinations from those from the parents.
Resting potential
An electrical potential across a cell membrane when not propagating an impulse.
Saprotorph
An organism that feeds on dead organic matter using extracellular digestion.
Sex chromosome
A chromosome that helps to determine the sex of an individual.
Sex linkage
Genes carried on sex chromosomes.
Species
A group of organisms which could interbreed and produce fertile offspring.
Synapse
The gap between neurons across which neurotransmitter diffuses.
Taxis
Locomotion of an organism in a particular direction in response to an external stimulus (eg., phototaxis to light and chemotaxis to gradients of dissolved substances).
Test cross
Testing a suspected heterozygote by crossing with a known homozygous recessive (The term backcross is no longer used).
Tissue
A group of cells of one type with similar structure and function (eg., plant parenchyma and squamous epithelium).
Translocation
The movement of substances from one part of a plant to another in the phloem.
Transpiration
The loss of water vapour from the leaves and stems of plants.
Trophic level
The position that an organism occupies in a food chain or group of organisms in a community that occupy the same position in food chains.
Universal
Found in all living organisms.
Water potential
A measure of the tendency of water to move between regions. In practice it is the force acting on water molecules in solution when separated from pure water by a membrane permeable to water only (ie., partly permeable).
Page design © by Harry Hildebrand, 1999