Glossary of Keywords for Unit 4

A glossary of keywords you must know for AQA A2 Biology Unit 4

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Biology Unit 4 Keywords
Ecology The study of the inter-relationships between organisms and their
Abiotic Factors Non-living components of the environment.
Biotic Factors Living components of the environment.
Biosphere Life-supporting layer of land, air and water that surrounds the Earth.
Ecosystem A self-contained functional unit made up of all the interacting biotic and
abiotic factors in a specific area.
Population A group of interbreeding organisms of one species in a habitat.
Community All the populations of organisms of different species in a particular
area at the same time.
Habitat The place where a community of organisms lives.
Niche All the resources and conditions required for an organism to survive,
reproduce and maintain a viable population.
Abundance The number of individuals of a species within a given space.
Mark-release-recapture Capture, count, mark.
Some time later, more individuals collected, marked counted.
Estimated population size = Total number in 1st sample x total number in 2nd sample
Number of marked individuals recaptured
Population size The number of individuals in a population.
Intraspecific competition Individuals of same species competing with one another for resources
such as food, water, breeding sites etc.
Interspecific competition Individuals of different species competing for resources.
Predator An organism that feeds on another organism.
Selection pressure The environmental force altering the frequency of alleles in a
Immigration Where individuals join a population from outside.
Emigration Where individuals leave a population.
Population growth = (births + immigration) ­ (deaths + emigration)
Percentage population Population change during period (increase/decrease by how many)
growth rate in a given Population at the start of the period x100
Birth rate Number of births per year x 100
Total population in the same year
Death rate Number of deaths per year x 100
Total population in the same year
Demographic transition The transition from high birth and death rates to low birth and death
rates as a country develops from a pre-industrial to an industrialized
economic system.
Average life expectancy The age at which 50% of the individuals within a population are still
Activation Energy Bonds are unstable and easy to break. (Bonds between phosphate

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Photophosphorylation The production of ATP using the energy of sunlight. Light energy is
used to create a high-energy electron donor and a lower-energy
electron acceptor. Electrons then move spontaneously from donor to
acceptor through an electron transport chain.
Oxidative phosphorylation A metabolic pathway that uses energy released by the oxidation of
nutrients to produce adenosine triphosphate (ATP).…read more

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Krebs Cycle Acetylcoenzyme A comes into a cycle of oxidation-reduction reactions
that yield some ATP and a large number of electrons.
Involves substrate-level phosphorylation.
Electron transport chain The use of the electrons produced in the Krebs cycle to synthesise ATP
with water produced as a by-product.
Energy and Ecosystems
Producers Organisms that manufacture organic substances using light energy,
water and carbon dioxide during photosynthesis.
Consumers Organisms that obtain their energy by feeding on other organisms
rather than using the light energy directly.…read more

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Nutrient Cycles
Base sequence of all
nutrient cycles
Greenhouse effect Natural process that occurs that keeps the average global
temperature around 17C. It is a result of the heat and light of the solar
radiation that reaches our planet and isn't reflected back into space.
Ammonification Saprobiotic organisms feed on organic ammonium containing
compounds, releasing ammonia which forms ammonium ions in the soil.
Nitrification An oxidation reaction that converts ammonium ions to nitrate ions and
releases energy. It is carried out my nitrifying bacteria.…read more

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Allele Different forms of a gene.
Homologous A pair of chromosomes that have the same gene loci and therefore
chromosomes determine the same features.
Homozygous Two of the same alleles present.
Heterozygous One of each allele present.
Dominant The allele that is expressed even when present with the recessive
Recessive The allele that is not expressed. Expressed only in the presence of
another identical allele.
Homozygous dominant Two dominant alleles.
Homozygous recessive Two recessive alleles.
Diploid 2 copies of each allele in cells.…read more


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