IB dictionary part 1

abiotic factor

a non-biological factor (eg. temperature) that is part of the environment of an organism

abscisic acid

a plant growth substance tending to inhibit growth

absorption spectrum

range of a pigment's ability to absorb various wavelengths of light

acetylcholine

a neurotransmitter, liberated at synapses in the CNS

acid rain

the coctail of chemical pollutants that may occur in the atmosphere

action potential

rapid change (depolarisation) in membrane potential of an excitable cell (eg. a neurone)

action spectrum

range of wavelengths of light within which a process like photosynthesis takes place

activation energy

energy a substrate molecule must have before it can undergo a chemical change

active site

region of enzyme molecule where substrate molecule binds

active transport

movement of substances across a membrane involving a carrier protein and energy from respiration

adenine

a purine organic base, found in the coenzymes ATP and NADP, and in nucleic acids (DNA and RNA) in which it pairs with tymine

adenosine diphosphate (ADP)

a nucleotide, present in every living cell, made of adenosine and two phosphate groups linked in series, and important in energy transport reactions of metabolism

adenosine triphosphate (ATP)

a nucleotide, present in every living cell, formed in photosynthesis and respiration from ADP and Pp and functioning in metabolism as a common intermediate between energy-requiring and energy-yielding reactions