a2 biology key words

Pregunta	Respuesta
ecosystem	more or less self-contained functional unit in ecology made up of all the interacting abiotic and biotic factors in an area
population	all the organisms of one species in a habitat
community	all the organisms of all the different species that live in the same area
habitat	place where an organism lives
Biotic factor	living factor of the organism's environment e.g. mutualism, disease and predation.
abiotic factor	non-living factor of the organism's environment e.g. temperature, pH, rainfall
niche	organisms role in an ecosystem governed by adaptation to biotic and abiotic conditions
percentage cover	estimate of the area within a quadrat that a particular plant species covers
frequency	likelihood of a particular species occurring in a quadrat
abundance	number of individuals of a species within a given space (measured by frequency, %cover and population density)
population density	number of individuals of a species present per metres squared (number of them in quadrat)
biodiversity	range and variety of living organisms within a particular area
Gene	section of DNA that codes for a polypeptide
Alleles	different versions of the same gene
Locus	specific position of a gene on a chromosome
Gamete	sex cells with haploid number of chromosomes
Homozygous	when an individual contains two identical alleles of the gene
Heterozygous	an individual that has two different alleles of the same gene
Dominant allele	always expressed in the phenotype if present
Recessive allele	only expressed in the phenotype if the individual is homozygous
Co-dominant alleles	both alleles contribute to the phenotype as both are equally dominant
Phenotype	characteristics of an organism resulting from both genotype and environment
Genotype	genetic constitution of an organism
Monohybrid inheritance	inheritance of a single characteristic controlled by one gene
Multiple alleles	when there are more than two alleles for a gene
succession	Change in species composition in an area over time due to environmental factors. Conditions change due to species present
allele frequency	number of times an allele occurs within the gene pool
biomass	total mass of living material in a specific area at a given time (usually measured as dry mass as amount of water in an organism is very variable)
climax community	a stable community of the organisms that make up the final stage of ecological succession
directional selection	selection that selects against one extreme in phenotype, shifting the mode. It normally occurs in a changing environment
stabilising selection	selection that selects against both extremes in phenotype, reducing the variation around the mode, which stays the same. It normally occurs in a stable environment
ectotherm	an animal that uses the environment and behaviour to regulate its body temperature
endotherm	an animal that maintains a constant body temperature by physiological mechanisms
effector	an organ that responds to stimulation by a nerve impulse, resulting in a change or response
receptor	a cell adapted to detect changes in the environment
gene pool	total number of alleles in a particular population at a specific time
gene therapy	where defective alleles are replaced with functional ones to treat genetic disorders
generator potential	depolarisation of the membrane of a receptor cell as a result of a stimulus
Conduction	The direct transfer of heat energy through matter. Heat causes particles to vibrate and gain kinetic E, making adjacent particles vibrate too. Occurs mainly in solids.
convection	Heat transfer due to movement of the warmed matter itself. Heat causes them to expand and move, carrying the heat that they absorbed with them. Occurs in fluids
Radiation	transfer of heat by infra-red waves, how we lose most of our heat
Evaporation	conversion of liquid water to vapour. Requires lots of heat energy which is gained by the water as it evaporates
Glycogenolysis	Breakdown of glycogen (stored in liver and muscle cells) to glucose
Gluconeogenesis	production of new glucose from sources other than carbohydrates e.g. lactate, glycerol and amino acids
Glycogenesis	conversion of glucose to glycogen (stored in the liver)
homeostasis	the maintenance of a more or less constant internal environment
interspecific competition	competition between organisms of different species
intraspecific competition	competition between organisms of the same species
introns	sections of non-coding DNA within a gene
mutation	change in the DNA base sequence
negative feed back	a change in the normal levels initiates a response which acts against the change to restore levels to normal
oncogenes	mutated versions of proto-oncogenes that result in increased cell division leading to growth of a tumour
pioneer species	The first species to colonise an inhospitable habitat. They are tolerant to hostile conditions, and alter them making them less hostile (e.g. add humus, increase soil nutrient content, change the pH)
recognition sequence	short and palindromic section of double stranded DNA to which a restriction endonuclease with a complementary active site can bind and cut
refractory period	period during which the axon membrane cannot be depolarised as Na+ ion channels are closed. NO NEW actions potentials can be initiated
salutatory conduction	occurs along myelinated neurones. localised currents arise between adjacent nodes of Ranvier which allow action potential to ‘jump’ from one node to the next
saprobiotic bacteria	secrete enzymes which break down dead/decaying matter extracellularly, before absorbing the products of digestion
selective breeding	breeding of an organism by human selection of parents in order to increase/eliminate certain characteristics
Totipotent	unspecialised and capable of expressing all its genes (e.g. embryonic stem cells)- can differentiate into any cell of that organism
Multipotent	cells that can only differentiate into a few closely related cell types (e.g. most adult stem cells)
Housekeeping genes	expressed in each of the organism’s cells e.g. genes coding for respiration enzymes
Somatic cells	cells that are not involved in reproduction
stem cells	cells that are unspecialised, can all divide and renew themselves over long periods and can develop into other specialised cell types. (two types: embryonic and adult)
sex-linked gene	gene carried on a sex chromosome (usually X as Y is much shorter)
homologous chromosomes	Chromosomes with same genes at same loci
what is a transect?	A method of systematic sampling. Line through habitat along which organisms are sampled and measurements are taken
monoculture	Same crop grown in large numbers over large area

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