OCR Biology Definitions (year 2)

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abiotic components

abiotic components

components of an ecosystem that are non-living

abiotic factors

non-living components of an ecosystem that affect other living components

accelerans nerve

branch of the sympathetic nervous system that speeds up heart rate

acetylcholine

chemical that acts as a transmitter by diffusing across synaptic cleft

acetylcholinesterase

an enzyme in the synaptic cleft that breaks down acetylcholine. After it has triggered an action potential in the post-synaptic neurone, acetylcholine must be broken down otherwise it would remain in the synaptic cleft and would continue to open sodium ion channels in the post-synaptic membrane, causing action potentials.

acinus (pl. acini)

small group of exocrine cells in a sac-like structure, in the pancreas these surround a tubule and secrete into the tubule

actin and myosin

proteins involved in muscular contraction

action potential

a brief reversal of the potential across the membrane of a neurone causing a peak of +40mV compared to the resting potential -60mV

adenyl cyclase

an intracellular enzyme that converts ATP to cyclic AMP (cAMP)

ADP

adenosine diphosphate

adrenal cortex

the outer layer oh the adrenal gland

adrenal gland

one of a pair pf glands lying above the kidneys

adrenaline

a hormone released from the medulla of the adrenal glands, which stimulates the body to prepare for fight or flight

adrenal medulla

the inner layer of the adrenal gland

adrenocorticotrophic hormone (ACTH)

a hormone released by the pituitary, which stimulates the adrenal cortex to produce corticosteroid hormones

adsorption

adhesion/binding to a surface

aerobic

in the presence of oxygen

agar

a polysaccharide of galactose obtained from seaweed, which is used to thicken the medium into a gel

agarose

a type of sugar which can be incorporated into a type of agar gel

alkaloids

organic nitrogen-containing bases that have important physiological effects on animals; includes nicotine, quinine, strychnine and morphine

allele

versions of a gene

allele frequency

proportion of a particular allele within a gene pool

allopatric speciation

formation of two different species from one original species, due to geographical isolation

alpha (α) cells

cells found in islets of Langerhans that secrete glucagon

ammonification

the production of ammonia by bacterial action in the decay of nitrogenous organic matter

AMP

adenosine monophosphate

anaerobic

in the absence of oxygen

aneuploidy

abnormal chromosome number

antagonist

something the works against another in opposite pairs, such as muscles arranged in opposing pairs, so one contracts as the other elongates

antidiuretic hormone (ADH)

a hormone, made in the hypothalamus, stored and released from the pituitary gland, that controls the permeability of the collecting duct walls in the kidneys

apical dominance

inhibition of lateral buds further down the shoot by chemicals produced by the apical bud at the tip of a plant shoot

apoptosis

programmed cell death

artificial selection

selective breeding of organisms to produce desired phenotypes

ascending limb

part of the loop of Henle that carries fluid back into the distal tubule in the cortex

aseptic technique

sterile techniques used in culturing and manipulating microorganisms

ATP

adenosine triphosphate

autoclave

a pressurised device (pressure cooker) used the sterilise equipment by heating to 120ºC

autoimmune response

a response in which the body’s immune system attacks and destroys some of its own cells

autonomic nervous system

part of the nervous system responsible for controlling the involuntary motor activities of the body

autoradiograms

photographs made when photographic fil is exposed to molecules labelled with radioactivity

autosomal linkage

gene loci present on the same autosome (non-sex chromosome) that are often inherited together

autosomes

chromosomes that are often inherited together

autotrophic nutrition

type of nutrition where organic molecules are synthesised from inorgancis molecules such as carbon dioxide and water; photosynthesis is one type of autotrophic nutrition where sunlight energy is converted to chemical energy that is used to synthesis large organic molecules from small inorganic molecules; chemosynthesis uses energy derived from chemical reactions (e.g. nitrifying bacteria in soil)

auxins

plant hormones responsible for regulation plant growth

belt transect

continuous belt or series of quadrants used to estimate the distribution of organisms across a certain area such as a meadow or seashore

beta (β) cells

cells found in the islets of Langerhans that secrete the hormone insulin

bioinformatics

transfer of biomass from one trophic level to another

biotechnology

the use of living organisms or parts of living organisms in industrial processes. This could be to produce food, drugs, or other products

biotic components

components of an ecosystem that are living

biotic factors

environmental factors of an ecosystem that are living organisms in an ecosystem that affect each other, e.g. predation, disease, competition, food availability