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GCSE Biology
nano-
A billionth of a unit, equal to 10−910^{-9}10−9 of that unit.
Nanometre
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A unit of length equal to 10−910^{-9}10−9 metres; its symbol is nm\text{nm}nm.
Nanometre (nm)
A unit equal to one billionth of a metre: 1 nm=10−9 m1\text{ nm}=10^{-9}\text{ m}1 nm=10−9 m.
Natural classification
A system that groups organisms according to their evolutionary relationships and shared ancestry, using evidence from several kinds of characteristic.
Natural pacemaker
A group of cells in the right atrium that produces electrical signals controlling the natural resting heart rate.
Natural selection
The process by which organisms with advantageous inherited characteristics are more likely to survive and reproduce, making those characteristics more common over generations.
Necrosis
Death of cells or tissues in a living organism.
Negative feedback
A control process in which a departure from the normal level causes responses that oppose the change and restore conditions towards normal.
Negative tropism
Growth away from a stimulus.
Nephron
A microscopic filtering unit in a kidney, consisting of Bowman’s capsule and a tubule that processes the filtrate.
Nervous system
The body's rapid communication system, made from the central nervous system and the neurones that connect it to receptors and effectors.
Net movement
The overall movement that remains after particle movements in opposite directions are taken into account.
Neuron
A specialised nerve cell that carries electrical impulses through the nervous system.
Neurone
A nerve cell that carries electrical impulses.
Neuroscience
The study of the nervous system, including how it functions and how its disorders might be treated.
Neurotransmitter
A chemical released from the end of a neurone that diffuses across a synaptic gap and can trigger a new electrical impulse in the next neurone.
Nitrate
A soluble nitrogen compound that plants absorb from soil through their roots and use to make amino acids and proteins.
Nitrate deficiency
A condition in which a plant lacks enough nitrate ions to make the proteins required for growth.
Nitrate ion
A nitrogen-containing ion absorbed from the soil and needed by plants to produce amino acids and then proteins.
Nitrification
The conversion of ammonium compounds into nitrites and then nitrates by bacteria in soil.
Nitrogen cycle
The movement and chemical transformation of nitrogen between the atmosphere, soil and living organisms.
Nitrogen fixation
The conversion of nitrogen gas from the air into nitrogen-containing compounds by nitrogen-fixing bacteria.
Non-coding DNA
DNA that does not code for a protein; some of it controls whether genes are switched on or off.
Non-communicable disease
A disease that cannot spread from one organism to another.
Non-hormonal contraception
Contraception that works without using hormones, for example by forming a barrier or using surgery.
Non-indigenous species
A species introduced to an area where it does not naturally occur.
Non-specific defence
A defence that acts against many different pathogens rather than recognising one particular antigen.
Nucleotide
A repeating unit of DNA containing a sugar, a phosphate group and one base.
Nucleus
The sub-cellular structure that contains genetic material and controls the activities of a eukaryotic cell.
Number
The amount of a particular object or event, usually found by counting.
1,308 key terms
