2.4.4 Define diffusion and osmosis

Diffusion:

The net movement of particles from a region of high concentration to a region of low concentration (along the gradient) until equilibrium

Osmosis:

The net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration until equilibrium is reached

3.6.1 Define enzyme and active site

Enzyme: A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold (i.e. a biological catalyst)

Active Site: The site on the surface of an enzyme which binds to the substrate molecule

3.6.4 Define denaturation

Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties

3.7.1 Define cell respiration

Cell respiration is the controlled release of energy from organic compounds in cells to form ATP

4.1.2 Define gene, allele and genome

Gene: A heritable factor that controls a specific characteristic, consisting of a length of DNA occupying a particular position on a chromosome (locus)

Allele: One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same locus as other alleles of the gene

Genome: The whole of the genetic information of an organism

4.1.3 Define gene mutation

Gene mutation: A change in the nucleotide sequence of a section of DNA coding for a particular feature

4.2.2 Define homologous chromosomes

Homologous chromosomes are chromosomes that share:

The same structural features (e.g. same size, same banding pattern, same centromere position)

The same genes at the same loci positions (while genes are the same, alleles may be different)

4.3.1 Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross

Genotype: The allele combination of an organism

Phenotype: The characteristics of an organism (determined by a combination of genotype and environmental factors)

Dominant Allele: An allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state

Recessive Allele: An allele that only has an effect on the phenotype when present in the homozygous state

Codominant Alleles: Pairs of alleles that both affect the phenotype when present in a heterozygote

Locus: The particular position on homologous chromosomes of a gene

Homozygous: Having two identical alleles of a gene

Heterozygous: Having two different alleles of a gene

Carrier: An individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele

Test Cross: Testing a suspected heterozygote by crossing it with a known homozygous recessive

4.3.7 Define sex linkage

Sex linkage refers to when a gene controlling a characteristic is found on a sex chromosome (and so we associate the trait with a predominant gender)

Sex-linked conditions are usually X-linked, as very few genes exist on the shorter Y chromosome

4.4.11 Define clone

A clone is a group of genetically identical organisms or a group of cells derived from a single parent cell

5.1.1 Define species, habitat, population, community, ecosystem and ecology

Species: A group of organisms that can interbreed and produce fertile, viable offspring

Habitat: The environment in which a species normally lives or the location of a living organism

Population: A group of organisms of the same species who live in the same area at the same time

Community: A group of populations living and interacting with each other in an area

Ecosystem: A community and its abiotic environment

Ecology: The study of relationships between living organisms and between organisms and their environment

Autotroph: An organism that synthesises its organic molecules from simple inorgance substances (e.g. CO2 and nitrates) - autotrophs are producers

Heterotroph: An organism that obtains organic molecules from other organisms - heterotrophs are consumers

5.1.6 Define trophic level

An organism's trophic level refers to the position it occupies in a food chain

5.4.1 Define evolution

Evolution is the cumulative change in the heritable characteristics of a population

6.3.1 Define pathogen

A pathogen is a disease-causing micro-organism, virus or prion

6.5.4 Define resting potential and action potential (depolarisation and repolarisation)

Resting Potential: The charge difference across the membrane when a neuron is not firing (-70 mV), as maintained by the sodium-potassium pump

Action Potential: The charge difference across the membrane when a neuron is firing (about 30 mV)

Depolarisation: The change from a negative resting potential to a positive action potential (caused by opening of sodium channels)

Repolarisation: The change from a positive action potential back to a negative resting potential (caused by opening of potassium channels)

D.3.2 Define half-life

The half life of a radioisotope is a measure of the time taken for the radioactivity to fall to half its original level

In other words, it is a measure of the time taken for half the atoms in a radioactive sample to decay

G.1.9 Define biomass

Biomass is the total dry organic matter of living organisms or ecosystems

G.2.1 Define gross production, net production and biomass

Gross Production: The amount of organic matter (biomass) produced by plants

Net Production: The amount of organic matter produced by plants minus what is needed for plant respiration

Biomass: The total dry organic matter of living organisms or ecosystems

G.3.7 Define biomagnification

Biomagnification is the process in which chemical substances become more concentrated at each trophic level