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Review of all IB Biology subjects.


the study of relationships between living organisms and between organisms and their environment


a system made up of organisms as well as the abiotic factors in the area


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


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


a group of organisms which can interbreed and produce fertile offspring


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


producers; they can make their own food


consumers; they feed on ready made organic material


organisms that feed on the detritus and decomposing organic material of living organisms


decomposers; organisms that feed on dead organisms and products of living organisms

carrying capacity

the maximum number of organisms of a species, or the maximum population size which an environment is able to support

random sample

a sample where every individual in a population has an equal chance of being chosen

trophic level

Position in the food chain, determined by the number of energy-transfer steps to that level; a functional classification of taxa within a community that is based on feeding relationships

standard deviation

used to summarize the spread of values around the mean; ∑((X-X)²/n-1)


a group of organisms with similar characteristics, which can interbreed and produce fertile offspring


unicellular and multicellular eukaryotic organisms; may be auto or heterotrophic and live in salt and fresh water


eukaryotic and feed by absorption of nutrients; cell walls are made of chitin


eukaryotic photosynthetic organisms; cell wall contains cellulose and cells contain chlorophyll


feed by ingestion


change in a gene pool of a species over a period of time


the number of years it takes for 50% of a sample to decay


a discrete structure within a cell, and has a specific function


measure size of diagram ÷ actual size of object


an integrated group of cells that share structure and are adapted to perform a similar function


a combination of two or more tissues which function as an integrated unit, performing one or more specific functions

organ system

a group of organs that specialize in a certain function together


movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient


passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration across a semi permeable membrane


molecules containing carbon that are found in living systems (Not CO2); often have covalent bonds


a globular protein that accelerates a specific reaction; catalysts that can be used over and over

active site

the region of an enzyme surface that binds to the substrate during the reaction catalyzed by the enzyme


a structural change in a protein that results in a loss of its biological properties


more than one codon can code for a single amino acid


codes are the same for all living organisms


the reassortment of genes into different combinations from the parents


a heritable factor that controls a specific characteristic consisting of a length of DNA occupying a specific position on a chromosome called a locus


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


the total genetic material of an organelle, organism, or cell

gene pool

the total of all genes carried by the individuals in a population

gene mutation

a change in the base sequence of a gene


the alleles possessed by an organism


the characteristics of an organism

dominant allele

an allele which as the same effect on the pheno type whether it is in a homozygous or heterozygous state

recessive allele

an allele which has an effect on the phenotype in the homozygous state

codominant alleles

alleles which have a partial effect in the heterozygous state but a more pronounced effect in the homozygous state


the position of a gene on the chromosome


having two copies of an allele


having different alleles of a gene


an individual that has a recessive allele that does not have an effect on the phenotype

test cross

testing a suspected heterozygote by crossing it with a known recessive homozygote

sex linkage

genes carried on the sex chromosomes, usually the X

linkage group

a group of genes whose loci are on the same chromosome

polygenic inheritance

the inheritance of a characteristic which is controlled by more than one gene

genetic screening

testing individuals in a population for the presence of a gene (or a certain allele of a gene)


a group of organisms of identical genotype or a group of cells descended from a single parent cell

cell respiration

the controlled release of energy in the form of ATP from organic compounds in cells


organisms that cause disease

active immunity

immunity due to production of antibodies by the organism itself after infection

passive immunity

immunity due to acquisition of antibodies from another source (can be injected by needle or passed through placenta or breast milk)

natural immunity

immunity due to infection

artificial immunity

immunity due to a vaccine

resting potential

electrical impulse across a cell membrane when not propagating an impulse

action potential

the localized reversal and then restoration of electrical potential between the inside and outside of a neuron as the impulse passes along it

innate behavior

behavior that normally occurs in all members of a species despite natural variation in environmental influences


locomotion in a particular direction in response to an external stimulus


movement in an organism where the rate depends on the stimulus

classical conditioning

modification of behavior in an animal as a result of the detection of correlations between external events

operant conditioning

a learning procedure in which a reinforcement follows a particular response


an attachment to an object encountered during a short period after birth, usually a parent

food chain

a linear and simple feeding relation, where one organism has one type of food and is eaten by one type of organism

food web

more complex than a food chain and it includes a larger variety of organisms, Each of which feed on a variety of other organisms and they are in turn fed on by more organisms

greenhouse effect

a NATURAL PHENOMENON that was required for life to form on the planet

energy flow (in a food chain)

energy losses between trophic levels include material not consumed or material not assimilated and heat loss through cell respiration

population size factors

if (natality + immigration) > (mortality + emigration) then a population is increasing

exponential phase

occurs when there are no controlling factors

transitional phase

the birthrate begins to decrease

plateau phase

occur as carrying capacity is reached

density dependent factors

more effect in crowded populations (predation and disease)

density independent factors

independent of population size (weather, natural disasters)

extrinsic population-regulating mechanisms

originate outside the population (food supply, natural enemies, disease, weather)

intrinsic population-regulating mechanisms

seen in the physiology or behavior (less offspring in crowded populations, mass migration)


prokaryotae, protoctista, fungi, plantae and animalia


unicellular organisms lacking a nucleus and other membrane-bound organelles; circular DNA

Taxa hierarchy

kingdom, phylum, class, order, family, genus and species

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