IB Biology – Definitions required by the syllabus
IB Biology syllabus – definitions
* Definition given in IB Biology syllabus
TOPIC
WORD
DEFINITION
Topic 1:
Cells
Organelle
A discrete structure within a cell, with a specific
function.*
A group of cells similar to each other, along with
their associated intercellular substances, which
perform the same function within a multicellular
organism.
A group of tissues which work together as a
single unit to perform a particular function within
a multicellular organism.
A group of organs, vessels, glands, other tissues,
and/or pathways which work together to perform
a body function within a multicellular organism.
The passive movement of molecules from a
region of high concentration to a region of low
concentration.
The passive movement of water molecules, across
a partially permeable membrane, from a region of
lower solute concentration to a region of higher
solute concentration.*
Compounds containing carbon that are found in
living organisms (except hydrogencarbonates,
carbonates and oxides of carbon).*
Proteins that act as biological catalysts, speeding
the rate at which biochemical reactions proceed
but not altering the direction or nature of the
reactions.
A specific region of an enzyme where a substrate
binds and catalysis takes place.
A structural change in a protein that results in a
loss (usually permanent) of its biological
properties. Refer only to heat and pH as agents.*
Having more than one base triplet to code for one
amino acid.*
Found in all living organisms.*
Tissue
Organ
Organ system
Diffusion
Osmosis
Topic 2: The
Chemistry of
Life
Organic
Enzyme
Active site
Denaturation
Degenerate
Universal
Cell respiration
Controlled release of energy in the form of ATP
from organic compounds in cells.*
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IB Biology – Definitions required by the syllabus
TOPIC
WORD
DEFINITION
Topic 3:
Genetics
Gene
Homologous
chromosomes
Genotype
A 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).*
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.*
The whole of the genetic information of an
organism.*
A 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.
A pair of chromosomes containing the same linear
gene sequences, each derived from one parent.
The alleles possessed by an organism.*
Phenotype
The characteristics of an organism.*
Allele
Genome
Gene mutation
Dominant allele An 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 allele An allele that only has an effect on the phenotype
when present in the homozygous state.*
Codominant
Pairs of alleles that both affect the phenotype
alleles
when present in a heterozygote. (The terms
incomplete and partial will no longer be used.)*
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 a recessive allele of a gene
that does not have an effect on their phenotype.*
Testing a suspected heterozygote by crossing it
with a known homozygous recessive. (The term
backcross is no longer used.)*
Genes found on sex chromosomes (X and Y
chromosomes) are said to be sex linked.
Testing an individual for the presence or absence
of a gene.*
A group of genetically identical organisms or a
group of cells artificially derived from a single
parent cell.*
Test cross
Sex linkage
Genetic
screening
Clone
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IB Biology – Definitions required by the syllabus
TOPIC
WORD
DEFINITION
Topic 4:
Ecology and
Evolution
Ecology
The study of relationships between living
organisms and between organisms and their
environment.*
A community and its abiotic environment.*
Ecosystem
Population
Community
Species
Habitat
Autotroph
(producer)
Heterotroph
(consumer)
Detritivore
Saprotroph
(decomposer)
Trophic level
Carrying
capacity
Random sample
Evolution
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.*
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.
An organism that requires chemical energy from
already formed organic molecules.
Animal that consumes decomposing organic
particles, deriving nutrition primarily from
microbes on the particles.
Organism that feeds by secreting digestive
enzymes onto its food source and absorbing the
products of digestion. Fungi and bacteria are
examples.
Stage in a food chain or web leading from
primary producers (lowest trophic level) through
primary consumers (herbivores) to secondary and
tertiary consumers (carnivores).
Maximum average number or biomass of
organisms that can be sustained in a habitat over
the long term. Usually refers to a particular
species, but can be applied to more than one.
A method to ensure that every individual in a
population has an equal chance of being observed.
The process of cumulative change in the heritable
characteristics of a population.*
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IB Biology – Definitions required by the syllabus
TOPIC
WORD
DEFINITION
Topic 5:
Human
Health and
Physiology
Pathogen
An organism or virus that causes a disease.*
Excretion
Topic 8:
Genetics
Recombination
This is a general term for the discharge of
substances from the body. Release of an absorbed
or endogenous substance or of a waste product, in
urine, faeces, or other products normally leaving
the body. Excretion of most chemical compounds
from the body occurs mainly through the kidney
and the gut, although volatile compounds may be
largely eliminated by exhalation. Excretion by
perspiration and through hair and nails may also
occur. Excretion by the gastrointestinal tract may
take place by various routes such as the bile, the
shedding of intestinal cells and transport through
the intestinal mucosa.
The reassortment of genes or characters into
different combinations from those of the parents.
Recombination occurs for linked genes by
crossing over and, for unlinked genes, by
chromosome assortment* due to random
alignment during metaphase I and II of meiosis.
Genes that are located on the same chromosome
are part of a linkage group; the closer together the
genes are, the lower the probability that they will
be separated by crossing-over during meiosis in,
and hence the greater the probability that they will
be inherited together.
A trait or characteristic that is influenced by the
expression of more than one gene, e.g. hair colour
in humans. Continuous variation occurs as a
result.
Linkage group
Polygenic
inheritance
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IB Biology – Definitions required by the syllabus
TOPIC
WORD
Topic 10:
Defence
Against
Infectious
Disease
Active immunity Immunity due to the production of antibodies by
the organism itself after the body’s defence
mechanisms have been stimulated by invasion of
foreign micro-organisms.*
Passive
Immunity due to the acquisition of antibodies
immunity
from another organism in which active immunity
has been stimulated, including via the placenta or
in colostrum.*
Natural
Immunity due to infection.*
immunity
Artificial
Immunity due to inoculation with vaccine.*
immunity
Resting
The difference in electrical charge across the
potential
plasma membrane of a neuron when not
conducting nerve impulses (i.e. resting). In
humans, the value is around -70mV, meaning the
inside is negative relative to the outside of the
cell.
Action potential Voltage change generated across the membrane of
a nerve or muscle cell when the cell is activated
by electrical, chemical or mechanical stimuli. In
humans, the value is around +40mV. The action
potential is propagated along the nerve by
voltage-gated ion channels.
Osmoregulation The control of the water balance of the blood,
tissue or cytoplasm of a living organism.*
Transpiration
The loss of water vapour from the leaves and
stems of plants.*
Pollination
The transfer of pollen from the male organ, where
it is formed, to the receptive region of a female
organ, e.g. from anther to stigma.
Gross
The amount of energy fixed by autotrophs, in kJ
production
m-2 yr-1.
Net production Gross production less the energy used by the
autotrophs for their own respiration, in kJ m-2 yr-1.
Biomass
A quantitative estimate of the entire amount of
living organisms in a particular habitat; it can be
measured in terms of volume, mass, or caloric
energy.
Partial pressure The pressure exerted by an individual gas in a
mixture of gases; measured in kPa (or mm Hg).
Topic 11:
Nerves,
Muscles and
Movement
Topic 12:
Excretion
Topic 13:
Plant Science
Option G:
Ecology and
Conservation
Option H:
Further
Human
Physiology
DEFINITION
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