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Need to know definitions IB Biology Syllabus 2009 Source:

2.4.4 Define diffusion

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


Osmosis is 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.

3.6.1 Define enzyme

Enzymes: Globular proteins which act as catalysts of chemical reactions.

active site

Active site: Region on the surface of an enzyme to which substrates bind and which catalyses a chemical reaction involving the substrates.

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. (The differences between structural
genes, regulator genes and genes coding for tRNA
and rRNA are not expected at SL).

Allele: 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.

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

4.1.3 Define gene mutation

Gene mutation: a change to the base sequence of a gene

4.2.2 Define homologous chromosomes

Homologous chromosomes: chromosomes with the same genes as each other, in the same sequence but do not necessarily have the same allele of those genes.

4.3.1 Define genotype,

Genotype: the alleles of an organism.


Phenotype: the characteristics of an organism.

dominant allele

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

recessive allele

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

codominant alleles

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


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.

Test cross: testing a suspected heterozygote by
crossing it with a known homozygous recessive.

4.3.7 Define sex linkage

Sex linkage: when the gene controlling the characteristic is located on the sex chromosome and so we associate the characteristic with gender.

4.4.11 Define clone

Clone: a group of genetically identical organisms or
a group of cells derived from a single parent cell.

5.1.1 Define species

Species: a group of organisms that can interbreed
and produce fertile 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


Ecology: the study of relationships between living
organisms and between organisms and their

5.1.6 Define trophic level.

Trophic level: the trophic level of an organism is its position in the food chain. Producers, primary consumers, secondary consumers and tertiary consumers are examples of trophic levels.

5.4.1 Define evolution

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

6.3.1 Define pathogen.

Pathogen: an organism or virus that causes a

6.5.4 Define resting potential and action
potential (depolarization and

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

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

9.2.5 Define transpiration.

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

10.2.4 Define linkage group.

Linkage group: A pair or set of genes on a chromosome which tend to be inherited together.

10.3.1 Define polygenic inheritance.

A single characteristic that is controlled by two or more genes

11.1.3 Define active

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

passive immunity.

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

11.3.1 Define excretion

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

11.3.5 Define osmoregulation.

Osmoregulation is the control of the water balance
of the blood, tissue or cytoplasm of a living

3.2.1 Distinguish between organic and
inorganic compounds.

Compounds containing carbon that are found
in living organisms (except hydrogencarbonates,
carbonates and oxides of carbon) are regarded as

5.1.2 autotroph

Autotroph: an organism that synthesizes its organic
molecules from simple inorganic substances.


Heterotroph: an organism that obtains organic
molecules from other organisms.

5.1.3 consumers,

Consumer: an organism that ingests other organic
matter that is living or recently killed.


Detritivore: an organism that ingests non-living
organic matter.


Saprotroph: an organism that lives on or in nonliving organic matter, secreting digestive enzymes
into it and absorbing the products of digestion.

6.1.6 absorption

Absorption occurs when the food enters the body as the food molecules pass through a layer of cells and into the bodies tissues. This occurs in the small intestine which has many villi that are specialised for absorption.


Assimilation occurs when the food molecules becomes part of the bodies tissue. Therefore, absorption is followed by assimilation.

6.3.5 Distinguish between antigens

Antigens are foreign substances which stimulate the production of antibodies.


Antibodies are proteins that defend the body against pathogens by binding to antigens on the surface of these pathogens and stimulating their destruction. Antibodies usually only bind to one specific antigen.

6.4.1 Distinguish between ventilation, gas
exchange and cell respiration.

Ventilation is the process of bringing fresh air into the alveoli and removing the stale air. It maintains the concentration gradient of carbon dioxide and oxygen between the alveoli and the blood in the capillaries (vital for oxygen to diffuse into the blood from the alveoli and carbon dioxide out of the blood into the alveoli).

gas exchange

Gas exchange is the process of swapping one gas for another. It occurs in the alveoli of the lungs. Oxygen diffuses into the capillaries from the air in the alveoli and carbon dioxide diffuses out of the capillaries and into the air in the alveoli.

cell respiration.

Cell respiration releases energy in the form of ATP so that this energy can be used inside the cell. Cell respiration occurs in the mitochondria and cytoplasm of cells. Oxygen is used in this process and carbon dioxide is produced.

7.3.2 Distinguish between the sense and
antisense strands of DNA.

The sense strand (coding strand) has the same base
sequence as mRNA with uracil instead of thymine.
The antisense (template) strand is the template of DNA which is transcribed.

9.3.2 Distinguish between pollination,
fertilization and seed dispersal.

Pollination = transfer of pollen grain from anther to stigma
Fertilization = Fusion of the male gamete (in the pollen grain) with female gamete (in ovule) to form a zygote
Seed dispersal = Seeds are moved away from parental plants to reduce competition.

10.2.2 Distinguish between autosomes and
sex chromosomes.

Sex chromosomes are the ones that determine your gender. These are X and Y (XX in females, XY in males).

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