Glossary of terms for biology SL at GN




Glossary of terms for biology SL at GN


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Glossary of terms for biology SL at GN


Glossary of terms for biology SL at GN.

The following are the definitions you will need to know during the IB biology course. Some of these definitions correspond to the command term “define” whereas others correspond to different command terms such as “state”, “outline” and “distinguish” where you may need a specific definition or concept.


Assessment statement



State that error bars are a graphical

representation of the variability of


Error bars can be used to show either the range of the data or the standard deviation.


State that the term standard deviation

is used to summarize the spread of

values around the mean, and that

68% of the values fall within one

standard deviation of the mean.

For normally distributed data, about 68% of all values lie within ±1 standard deviation (s or σ) of the mean. This rises to about 95% for ±2 standard deviations.


State that multicellular organisms

show emergent properties.

Emergent properties arise from the interaction of component parts: the whole is greater than the sum of its parts.


Define diffusion and osmosis

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


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.


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 organic.


All compounds that contain no carbon are inorganic


Define enzyme and active site.

Enzymes are globular proteins which act as a catalysts of chemical reaction

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


Define denaturation.

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


Define cell respiration.

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


Define gene, allele and genome.

Gene: a heritable factor that controls a specific characteristic.


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.


Define gene mutation.

Is a change to the base sequence of a gene.


Define homologous chromosomes.

Chromosomes which have the same genes as each other, in the same sequence, but not necessarily the same alleles of those genes.


Define genotype, phenotype,

dominant allele, recessive allele,

codominant alleles, locus, homozygous, heterozygous, carrier and test cross.

Genotype: the alleles of an organism.


Phenotype: the characteristics of an organism.


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


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


Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote.

(The terms incomplete and partial dominance are

no longer 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 one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.


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


Define sex linkage.

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


Define clone.

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


Define species, habitat, population,

community, ecosystem and ecology

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 environment.


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


Distinguish between autotroph and


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


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


Distinguish between consumers,

detritivores and saprotrophs.

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.


Define trophic level.

The trophic level of an organism is its position in the food chain.


Outline the precautionary principle.

The precautionary principle holds that, if the effects of a human-induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding. This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going



Define evolution.

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


Distinguish between absorption and


Absorption: The process of taking in substances trough a layer of cells in the body´s tissues. It happens mainly in the small intestine.


Assimilation: once food particles are absorbed, they become part of the structure of the body.


Define pathogen.

Pathogen: an organism or virus that causes a disease.


Distinguish between antigens and


Antigens are foreign substances that stimulate the production of antibodies


Antibodies are proteins that recognize and bind to specific antigens.


Distinguish between ventilation, gas

exchange and cell respiration.

Ventilation is the process of bringing in fresh air to the alveoli and removing stale air.


Gas exchange is the process of swapping one gas for another in the alveoli.


Define resting potential and action

potential (depolarization and


Resting potential: Is the electrical potential across the plasma membrane of a cell that is not conducting an impulse. The inside of the neuron develops a net negative charge compare with the outside.


Action potential is 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)


Define nutrient.

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


Distinguish between minerals and

vitamins in terms of their chemical


Minerals are elements in ionic form.


Vitamins are organic compounds.


Distinguish, using the body mass

index, between being underweight,

normal weight, overweight and obese.

BMI = (mass in kg)/(height in m)2         Status

below 18.5                                        underweight

18.5–24.9                                         normal weight

25.0–29.9                                         overweight

30.0 and above                                obese


Distinguish between fundamental and

realized niches.

The fundamental niche of a species is the potential mode of existence, given the adaptations of the species.


The realized niche of a species is the actual mode of existence, which results from its adaptations and competition with other species.


Define biomass.

Biomass is the total dry mass of organic matter in organisms or ecosystems.


Define gross production, net

production and biomass.

Gross production is the total amount of organic matter produced by plants in an ecosystem. It is measured in Kilojoules of energy per square metre per year (Kj m-2 year-1)


Net Production is the amount of gross production in an ecosystem remaining after subtracting the amount used by plants in respiration.


Distinguish between primary and secondary succession, using an example of each.

Primary succession starts in an environment where living organism have not previously existed, for example a new volcanic island.



Secondary succession occurs in areas where an ecosystem is present, but it is replaced by other ecosystems. For example, abandoned farmlands developing into a forest.


Distinguish between biome and biosphere.

Biome is a type of an ecosystem.


Biosphere is the group of biomes of the world together


Define biomagnification.

Biomagnification is a process in which chemical substances become more concentrated at each trophic level.


The following table has all of the units and formula equations you should know about.


Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit.

Molecules (1 nm)

Thickness of membranes (10 nm),

Viruses (100 nm)

Bacteria (1 μm)

Organelles (up to 10 μm)

Most cells (up to 100 μm).


Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification.

Magnification = size of image/size of specimen

1000mm = 1 m; 1000 um = 1 mm; 1000 nm = 1 um


Explain reasons for the shape of pyramids of energy.

A pyramid of energy shows the flow of energy from one trophic level to the next in a community. The units of pyramids of energy are, therefore, energy per unit area per unit time, for example, kJ m–2 yr–1.


Compare the energy content per 100 g of carbohydrate, fat and protein.

Carbohydrates contain approximately 1,760 kJ per 100 g; Proteins 1,720 kJ per 100 g and Fats 4,000 kJ per 100 g.


Calculate body mass index (BMI) from the body mass and height of a person.

BMI = (mass in kg)/(height in m)2


Calculate values for gross production

and net production using the equation:

gross production – respiration = net production.

GP – R = NP


Construct a pyramid of energy, given appropriate information.

The units are kJ m–2 yr–1.


Calculate the Simpson diversity index for two local communities.


D = diversity index

 N = total number of organisms of all species found and n = number of individuals of a particular species.


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