IB Biology Definitions 2009 – 2013/14. 2.4.4 Define diffusion. Define diffusion.

IB BiologyIB BiologyDefinitionsDefinitions

2009 – 2013/142009 – 2013/14

2.4.42.4.4

Define Define diffusiondiffusion..

DiffusionDiffusion is the passive movement is the passive movement of particles from a region of high of particles from a region of high concentration to a region of low concentration to a region of low concentration.concentration.

2.4.42.4.4

Define Define osmosisosmosis..

OsmosisOsmosis is the passive movement of is the passive movement of water molecules, across a partially water molecules, across a partially permeable membrane, from a region permeable membrane, from a region of lower solute concentration to a of lower solute concentration to a region of higher solute concentration.region of higher solute concentration.

3.6.13.6.1

Define Define enzymeenzyme..

EnzymeEnzyme is a globular protein is a globular protein functioning as a biological catalyst in functioning as a biological catalyst in chemical reactions.chemical reactions.

3.6.13.6.1

Define Define active siteactive site..

Active siteActive site is the site (region) on is the site (region) on surface of enzyme to which substrate surface of enzyme to which substrate or substrates bind and which or substrates bind and which catalyses a chemical reaction catalyses a chemical reaction involving the substrate.involving the substrate.

3.6.43.6.4

Define Define denaturationdenaturation..

DenaturationDenaturation is a structural change is a structural change in a protein that results in the loss in a protein that results in the loss (usually permanent) of its biological (usually permanent) of its biological properties. properties. Refer only to heat and pH Refer only to heat and pH as agents.as agents.

3.7.13.7.1

DefineDefine cell respiration cell respiration..

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

4.1.24.1.2

Define Define genegene..

GeneGene is a heritable factor that is a heritable factor that controls a specific characteristic. controls a specific characteristic.

4.1.24.1.2

Define Define alleleallele..

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

4.1.24.1.2

Define Define genomegenome..

Genome Genome is the whole of the genetic is the whole of the genetic information of an organism.information of an organism.

4.1.34.1.3

Define Define gene mutationgene mutation. .

Gene mutationGene mutation is a gene mutation is a gene mutation is a change to the base sequence of is a change to the base sequence of a gene. a gene.

4.2.24.2.2

DefineDefine homologous homologous chromosomeschromosomes..

Homologous chromosomesHomologous chromosomes have have the same genes as each other, in the the same genes as each other, in the same sequence, but not necessarily same sequence, but not necessarily the same alleles of those genes. the same alleles of those genes.

4.3.14.3.1

Define Define genotypegenotype..

GenotypeGenotype is the alleles of an is the alleles of an organism.organism.

4.3.14.3.1

Define Define phenotypephenotype..

PhenotypePhenotype is the characteristics of is the characteristics of an organism.an organism.

4.3.14.3.1

Define Define dominant alleledominant allele..

Dominant alleleDominant allele is an allele that is an allele that has the same effect on the has the same effect on the phenotype whether it is present in phenotype whether it is present in the homozygous or heterozygous the homozygous or heterozygous state. state.

4.3.14.3.1

Define Define recessive allelerecessive allele..

Recessive alleleRecessive allele is an allele that is an allele that only has an effect on the phenotype only has an effect on the phenotype when present in the homozygous when present in the homozygous state. state.

4.3.14.3.1

Define Define codominant allelescodominant alleles..

Codominant allelesCodominant alleles is pairs of is pairs of alleles that both affect the alleles that both affect the phenotype when present in a phenotype when present in a heterozygote. (The terms incomplete heterozygote. (The terms incomplete and partial dominance are no longer and partial dominance are no longer used.)used.)

4.3.14.3.1

Define Define locuslocus..

LocusLocus is the particular position on is the particular position on homologous chromosomes of a gene.homologous chromosomes of a gene.

4.3.14.3.1

Define Define homozygoushomozygous..

HomozygousHomozygous is having two identical is having two identical alleles of a gene. alleles of a gene.

4.3.14.3.1

Define Define heterozygousheterozygous..

HeterozygousHeterozygous is having two is having two different alleles of a gene. different alleles of a gene.

4.3.14.3.1

Define Define carriercarrier..

CarrierCarrier is an individual that has one is an individual that has one copy of a recessive allele that causes copy of a recessive allele that causes a genetic disease in individuals that a genetic disease in individuals that are homozygous for this allele. are homozygous for this allele.

4.3.14.3.1

Define Define test crosstest cross..

Test crossTest cross is testing a suspected is testing a suspected heterozygote by crossing it with a heterozygote by crossing it with a known homozygous recessive. known homozygous recessive. (The (The term backcross is no longer used.)term backcross is no longer used.)

4.3.74.3.7

Define Define sex linkagesex linkage..

Sex linkageSex linkage is the association of a is the association of a characteristic with gender, because characteristic with gender, because the gene controlling the the gene controlling the characteristic is located on a sex characteristic is located on a sex chromosome. chromosome.

4.4.114.4.11

Define Define cloneclone. .

CloneClone is a group of genetically is a group of genetically identical organisms or a group of identical organisms or a group of cells derived from a single parent cells derived from a single parent cell.cell.

5.1.15.1.1

Define Define speciesspecies..

SpeciesSpecies is a group of organisms that is a group of organisms that can interbreed and produce fertile can interbreed and produce fertile offspring. offspring.

5.1.15.1.1

Define Define habitathabitat..

HabitatHabitat is the environment in which is the environment in which a species normally lives or the a species normally lives or the location of a living organism.location of a living organism.

5.1.15.1.1

Define Define populationpopulation..

PopulationPopulation is a group of organisms is a group of organisms of the same species who live in the of the same species who live in the same area at the same time. same area at the same time.

5.1.15.1.1

Define Define communitycommunity..

CommunityCommunity is a group of is a group of populations living and interacting populations living and interacting with each other in an area. with each other in an area.

5.1.15.1.1

Define Define ecosystemecosystem..

EcosystemEcosystem is a community and its is a community and its abiotic environment. abiotic environment.

5.1.15.1.1

Define Define ecologyecology..

EcologyEcology is the study of relationships is the study of relationships between living organisms and between living organisms and between organisms and their between organisms and their environment.environment.

5.1.65.1.6

Define Define trophic leveltrophic level..

Trophic levelTrophic level is the position that an is the position that an organism occupies in a food chain or organism occupies in a food chain or a group of organisms in a community a group of organisms in a community that occupy the same position in that occupy the same position in food chains. food chains.

5.4.15.4.1

Define Define evolutionevolution. .

EvolutionEvolution is the cumulative change is the cumulative change in the heritable characteristics of a in the heritable characteristics of a population. population.

6.3.16.3.1

Define Define pathogenpathogen. .

PathogenPathogen is an organism or virus is an organism or virus that causes a disease.that causes a disease.

6.5.46.5.4

Define Define resting potential.resting potential.

Resting potentialResting potential is t is the electrical he electrical potential across the plasma potential across the plasma membrane of a cell that is not membrane of a cell that is not conducting an impulse.conducting an impulse.

6.5.46.5.4

Define Define action potentialaction potential (depolarization & (depolarization & repolarization).repolarization).

Action potentialAction potential is t is the reversal he reversal (depolarization) and restoration (depolarization) and restoration (repolarization) of the electrical (repolarization) of the electrical potential across the plasma potential across the plasma membrane of a cell, as an electrical membrane of a cell, as an electrical impulse passes along it. impulse passes along it.

9.2.59.2.5

Define Define transpirationtranspiration..

TranspirationTranspiration is the loss of water is the loss of water vapour from the leaves and stems of vapour from the leaves and stems of plants. plants.

10.2.410.2.4

Define Define linkage grouplinkage group..

Linkage groupLinkage group is all the genes that is all the genes that have their loci on the same have their loci on the same chromosome. chromosome.

10.3.110.3.1

Define Define polygenic polygenic inheritanceinheritance..

Polygenic inheritancePolygenic inheritance is a is a characteristic controlled by more than characteristic controlled by more than one gene. one gene.

Polygenic inheritance is often due to co-Polygenic inheritance is often due to co-dominant genes. dominant genes.

They contribute to continuous variation They contribute to continuous variation like the skin colour. like the skin colour.

Other example is grain colour in wheat. Other example is grain colour in wheat.

11.1.311.1.3

Define Define active immunityactive immunity..

Active immunityActive immunity is immunity due to is immunity due to the production of antibodies by the the production of antibodies by the organism itself after the body’s organism itself after the body’s defence mechanisms have been defence mechanisms have been stimulated by antigens. stimulated by antigens.

11.1.311.1.3

Define Define passive passive immunity.immunity.

Passive immunityPassive immunity is immunity due is immunity due to the acquisition of antibodies from to the acquisition of antibodies from another organism in which active another organism in which active immunity has been stimulated, immunity has been stimulated, including via the placenta, colostrum, including via the placenta, colostrum, or by injection of antibodies.or by injection of antibodies.

11.3.111.3.1

Define Define excretionexcretion..

ExcretionExcretion is the removal from the is the removal from the body of the waste products of body of the waste products of metabolic pathways.metabolic pathways.

11.3.511.3.5

Define Define osmoregulationosmoregulation..

OsmoregulationOsmoregulation is the control of is the control of the water balance of the blood, the water balance of the blood, tissue or cytoplasm of a living tissue or cytoplasm of a living organism. organism.

E.1.1E.1.1

Define the term Define the term stimulus stimulus in the context of animal in the context of animal behaviour.behaviour.

A A stimulusstimulus is a change in the is a change in the environment (internal or external) environment (internal or external) that is detected by a receptor and that is detected by a receptor and elicits a response. elicits a response.

E.1.1E.1.1

Define the term Define the term responseresponse in the context of animal in the context of animal behaviour.behaviour.

A A responseresponse is a response to a is a response to a stimulus, a change in the stimulus, a change in the environment (internal or external) environment (internal or external) that is detected by a receptor. that is detected by a receptor.

E.1.1E.1.1

Define the term Define the term reflexreflex in in the context of animal the context of animal behaviour.behaviour.

A reflexA reflex is a rapid, unconscious is a rapid, unconscious response to a stimulus.response to a stimulus.

A.1.1A.1.1

Define Define nutrientnutrient..

NutrientNutrient is a chemical substance is a chemical substance found in foods that is used in the found in foods that is used in the human body.human body.

H.6.1H.6.1

Define Define partial pressurepartial pressure..

Partial pressurePartial pressure is the pressures is the pressures exerted by each of the gases in a exerted by each of the gases in a mixture of gases. mixture of gases.

The pressure of a gas in a mixture is The pressure of a gas in a mixture is the same as it would exert if it the same as it would exert if it occupied the same volume alone at occupied the same volume alone at the same temperature (Dalton's the same temperature (Dalton's Law).Law).