Cie biology terms

Definitions

α cell (alfa cell)

a cell in the islets of Langerhans in the pancreas that senses when blood glucose levels are low and secretes glucagon in response

abiotic factor

a physical characteristic of a habitat, such as temperature, light intensity and soil pH

abscisic acid (ABA)

an inhibitory plant growth regulator that causes closure of stomata in dry conditions

absorption spectrum

a graph of the absorbance of different wavelengths of light by a compound such as a photosynthetic pigment

accessory pigment

a pigment that is not essential to photosynthesis but which absorbs light of different wavelengths and passes the energy to chlorophyll a

acetylcholine (ACh)

a transmitter substance found, for example, in the presynaptic neurone at neuromuscular junctions

acetylcholinesterase

an enzyme that rapidly breaks down acetylcholine at synapses

actin

the protein that makes up the thin filaments in striated muscle

action potential

a brief change in the potential difference across cell surface membranes of neurones and muscle cells caused by the inward movement of sodium ions followed by the outward movement of potassium ions; it rapidly travels along the length of the neurone

action spectrum

a graph showing the effect of different wavelengths of light on a process, e.g. on the rate of photosynthesis

adrenaline (epinephrine)

a hormone secreted by the adrenal glands in times of stress or excitement

aerenchyma

plant tissue containing air spaces

afferent

leading towards; e.g. the afferent blood vessel leads towards a glomerulus

agarose gel

a jelly made from agar, used in electrophoresis alcoholic fermentation anaerobic respiration in which glucose is converted to ethanol

aleurone layer

a layer of tissue around the endosperm in a cereal seed that synthesises amylase during germination

alien species

a species that has been moved into a new ecosystem where it was previously unknown; also known as invasive species

allele

a particular variety of a gene

allopatric speciation

speciation that takes place as a result of two populations living in different places and having no contact with each other

allopolyploid

possessing more than two sets of chromosomes, where the chromosomes come from two different species

all-or-nothing law

a law that states neurones and muscle cells only transmit impulses if the initial stimulus is sufficient to increase the membrane potential above a threshold potential

amniocentesis

taking a small sample of amniotic fluid during the 15th or 16th week of pregnancy, so that the genotype of the fetus can be determined

Animalia

one of the four kingdoms of the domain Eukarya; eukaryotic organisms which are multicellular and heterotrophic and have a nervous system

antidiuretic hormone (ADH)

a hormone secreted from the pituitary gland that increases water reabsorption in the kidneys and therefore reduces water loss in urine

Archaea

a domain of prokaryotic organisms that resemble bacteria but share some features with eukaryotes

artificial insemination (AI)

injection of semen collected from a male into the uterus

artificial selection

the selection by humans of organisms with desired traits

ATP

adenosine triphosphate - the universal energy currency of cells

ATP synthase

the enzyme catalysing the phosphorylation of ADP to ATP

Autopolyploid

possessing more than two sets of chromosomes, where all the sets are from the same species

Autosomes

all the chromosomes except the X and Y (sex) chromosomes

Autotroph

an organism that can trap an inorganic carbon source (carbon dioxide) using energy from light or from chemicals

Auxin

a plant growth regulator (plant hormone) that stimulates cell elongation

Axon

a long cytoplasmic process of a neurone

β cell (beta cell)

a cell in the islets of Langerhans in the pancreas that senses when blood glucose levels are high and secretes insulin in response

β-galactosidase

an enzyme which catalyses the hydrolysis of lactose to glucose and galactose

Bacteria

the domain that contains all prokaryotic organisms except those classified as Archaea

Biodiversity

the variety of ecosystems and species in an area and the genetic diversity within species

Bioinformatics

the collection, processing and analysis of biological information and data using computer software

Biosensor

a device that uses a biological material such as an enzyme to measure the concentration of a chemical compound

biotic factor

a factor which affects a population or an environment, that is caused by living organisms; examples include competition, predation and parasitism

birth control pill

a pill that contains oestrogen and/or progesterone to prevent ovulation

Bowman's capsule

the cup-shaped part of a nephron that surrounds a glomerulus and collects filtrate from the blood

bundle sheath cells

a ring of cells in the leaves of C4 plants in which the Calvin cycle takes place out of contact with the air spaces in the leaf

C3 plant

a plant in which the first product of photosynthesis is a three-carbon compound

C4 plant

a plant in which the first product of photosynthesis is a four-carbon compound; most tropical grasses (but not rice) are C4 plants

calorimeter

the apparatus in which the energy value of a compound can be measured by burning it in oxygen

Calvin cycle

a cycle of reactions in photosynthesis in which carbon dioxide is fixed into carbohydrate

carotenoid

a yellow, orange or red plant pigment used as an accessory pigment in photosynthesis

CFTR

a transmembrane protein that controls the transport of chloride ions out of cells; CFTR written in italics refers to the gene for the CFTR protein

chemiosmosis

the synthesis of ATP using energy stored as a difference in hydrogen ion concentration across a membrane in a chloroplast or mitochondrion

chemoautotroph

autotroph such as a nitrifying bacterium that uses a chemical energy source

chemoreceptor

a receptor cell that responds to chemical stimuli; chemoreceptors are found in taste buds on the tongue, in the nose and in blood vessels where they detect changes in oxygen and carbon dioxide concentrations

chiasma (plural: chiasmata)

the visible effect(s) of crossing over

chi-squared (χ2) test

a statistical test that can be used to determine whether any difference between observed results and expected results is significant or is due to chance

chlorophyll

a green pigment responsible for light capture in photosynthesis in algae and plants

cholinergic synapse

a synapse at which the transmitter substance is acetylcholine

chorionic villus sampling

taking a small sample from one of the villi in the placenta, between the tenth and 13th week of pregnancy, so that the genotype of the fetus can be determined

chromatid

one of two identical parts of a chromosome, held together by a centromere, formed during interphase by the replication of the DNA strand

chromatin

the loosely coiled form of chromosomes during interphase of the cell cycle; chromatin is made of DNA and proteins and is visible as loosely distributed patches or fibres within the nucleus when stained

chromosome

a structure made of DNA and histones, found in the nucleus of a eukaryotic cell; the term bacterial chromosome is now commonly used for the circular strand of DNA present in a prokaryotic cell

chromosome mutation

a random and unpredictable change in the structure or number of chromosomes in a cell

codominant

two alleles are said to be codominant when both alleles have an effect on the phenotype of a heterozygous organism

collecting duct

the last section of a nephron, from which water can be absorbed back into the bloodstream before the urine flows into the ureter

community

all of the living organisms, of all species, that are found in a particular ecosystem at a particular time

control experiment

an experiment in which the factor whose effect is being investigated (the independent variable) is absent; it is used as a standard of comparison

corpus luteum

the 'yellow body' that develops from an ovarian follicle after ovulation

counter-current multiplier

an arrangement in which fluid in adjacent tubes flows in opposite directions, allowing relatively large differences in concentration to be built up

creatinine

a nitrogenous excretory substance produced from the breakdown of creatine

crista (plural: cristae)

a fold of the inner membrane of the mitochondrial envelope on which are found stalked particles of ATP synthase and electron transport chains associated with aerobic respiration

crossing over

an event that occurs during meiosis I, when chromatids of two homologous chromosomes break and rejoin so that a part of one chromatid swaps places with the same part of the other

cystic fibrosis

a genetic disease caused by a recessive allele of the CFTR (cystic fibrosis transmembrane regulator) gene

cytokinins

plant growth regulators that stimulate cell division

deamination

the breakdown of excess amino acids in the liver, by the removal of the amine group; ammonia and eventually urea are formed from the amine group

dendrite

a short cytoplasmic process of a neurone that receives nerve impulses from other neurones

dependent variable

in an experiment, the variable that changes as a result of changing the independent variable

depolarisation

the reversal of the resting potential across the cell surface membrane of a neurone or muscle cell, so that the inside becomes positively charged compared with the outside

diabetes

an illness in which the pancreas does not make sufficient insulin, or where cells do not respond appropriately to insulin

dihybrid cross

a genetic cross in which two different genes are considered

directional selection

a type of selection in which the most common varieties of an organism are selected against, resulting in a change in the features of the population

disruptive selection

natural selection that favours the survival of individuals at two different points within the range of variation, resulting in two different phenotypes

domain

one of the three major groups into which all organisms are classified

dominant

an allele is said to be dominant when its effect on the phenotype of a heterozygote is identical to its effect in a homozygote

ecosystem

all the living organisms of all species (the biotic component) and all the non-living components (the abiotic component) that are found together in a defined area and that interact with one another

effector

an organ or tissue that carries out an action in response to a stimulus; muscles and glands are effectors

efferent

leading away from

electrochemical gradient

a gradient across a cell surface membrane that involves both a difference in concentrations of ions and a potential difference e.g. the entry of sodium ions into neurones

electron transport chain

chain of adjacently arranged carrier molecules in the inner mitochondrial membrane, along which electrons pass by redox reactions

embryo transfer

embryos are removed from a female mammal and transferred to one or more surrogate mothers to complete development until birth

endocrine gland

a gland that secretes its products, which are always hormones, directly into the blood

endosperm

a tissue that stores food in some seeds, such as cereal grains

Eukarya

domain that contains all eukaryotic organisms: protoctists, fungi, plants and animals

evolution

changes in a population that may lead to speciation or extinction

excretion

the removal of toxic or waste products of metabolism from the body

expansins

proteins in the cell walls of plants that loosen the attachment of microfibrils of cellulose during elongation growth

F1

the offspring resulting from a cross between an organism with a homozygous dominant genotype, and one with a homozyogus recessive genotype

F2

the offspring resulting from a cross between two F1 (heterozygous) organisms

factor VIII

one of several substances that must be present in blood in order for clotting to occur

fitness

the probability of an organism surviving and reproducing in the environment in which it is found

follicle stimulating hormone (FSH)

glycoprotein hormone secreted by anterior pituitary gland to stimulate the development of follicles in the ovary

Fungi

one of the four kingdoms of the domain Eukarya; eukaryotic organisms which do not photosynthesise and have cell walls but without cellulose