IB Biology syllabus definitions Essays - Classical Genetics

IB Biology syllabus definitions Essays - Classical Genetics IB Biology syllabus definitions * Definition given in IB Biology syllabus TOPICWORDDEFINITION Topic 1: CellsOrganelleA discrete structure within a cell, with a specific function.* TissueA group of cells similar to each other, along with their associated intercellular substances, which perform the same function within a multicellular organism. OrganA group of tissues which work together as a single unit to perform a particular function within a multicellular organism. Organ systemA group of organs, vessels, glands, other tissues, and/or pathways which work together to perform a body function within a multicellular organism. Diffusion The passive movement of molecules from a region of high concentration to a region of low concentration. OsmosisThe passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.* Topic 2: The Chemistry of LifeOrganicCompounds containing carbon that are found in living organisms (except hydrogencarbonates, carbonates and oxides of carbon).* EnzymeProteins that act as biological catalysts, speeding the rate at which biochemical reactions proceed but not altering the direction or nature of the reactions. Active siteA specific region of an enzyme where a substrate binds and catalysis takes place. DenaturationA structural change in a protein that results in a loss (usually permanent) of its biological properties. Refer only to heat and pH as agents.* DegenerateHaving more than one base triplet to code for one amino acid.* UniversalFound in all living organisms.* Cell respirationControlled release of energy in the form of ATP from organic compounds in cells.* TOPICWORDDEFINITION Topic 3: GeneticsGeneA heritable factor that controls a specific characteristic. (The differences between structural genes, regulator genes and genes coding for tRNA and rRNA are not expected at SL).* AlleleOne 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.* GenomeThe whole of the genetic information of an organism.* Gene mutationA change in the base sequence of a gene on DNA. This could be by substitution, deletion, or insertion of a base or bases. The terms point mutation or frameshift mutation will not be used. Homologous chromosomesA pair of chromosomes containing the same linear gene sequences, each derived from one parent. GenotypeThe alleles possessed by an organism.* PhenotypeThe characteristics of an organism.* Dominant alleleAn allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state.* Dominant alleles mask the effects of recessive alleles. Recessive alleleAn allele that only has an effect on the phenotype when present in the homozygous state.* Codominant allelesPairs of alleles that both affect the phenotype when present in a heterozygote. (The terms incomplete and partial will no longer be used.)* LocusThe particular position on homologous chromosomes of a gene.* HomozygousHaving two identical alleles of a gene.* HeterozygousHaving two different alleles of a gene.* CarrierAn individual that has a recessive allele of a gene that does not have an effect on their phenotype.* Test crossTesting a suspected heterozygote by crossing it with a known homozygous recessive. (The term backcross is no longer used.)* Sex linkageGenes found on sex chromosomes (X and Y chromosomes) are said to be sex linked. Genetic screeningTesting an individual for the presence or absence of a gene.* CloneA group of genetically identical organisms or a group of cells artificially derived from a single parent cell.* TOPICWORDDEFINITION Topic 4: Ecology and EvolutionEcologyThe study of relationships between living organisms and between organisms and their environment.* EcosystemA community and its abiotic environment.* PopulationA group of organisms of the same species who live in the same area at the same time.* CommunityA group of populations living and interacting with each other in an area.* SpeciesA group of organisms which can interbreed and produce fertile offspring.* HabitatThe environment in which a species normally lives or the location of a living organism.* Autotroph (producer)An organism that fixes chemical energy in the form of organic molecules; it "makes its own food" and does not require previously formed organic materials from the environment; e.g. photoautotroph, chemoautotroph. Heterotroph (consumer)An organism that requires chemical energy from already formed organic molecules. DetritivoreAnimal that consumes decomposing organic particles, deriving nutrition primarily from microbes on the particles. Saprotroph (decomposer)Organism that feeds by secreting digestive enzymes onto its food source and absorbing the products of digestion. Fungi and bacteria are examples. Trophic levelStage in a food chain or web leading from primary producers (lowest trophic level) through primary consumers (herbivores) to secondary and tertiary