Glossary

An A-Z of keywords and phrases, all of which are relevant to the post-16 biology curriculum.

 

A B C D E F G H I J K L M N O P Q R S T U V W Y Z
NAD (nicotinamide adenine dinucleotide)

A coenzyme that acts as a hydrogen acceptor in respiration. NAD accepts hydrogen in the link reaction and the Krebs cycle and becomes reduced. In the electron transport chain, it transfers electrons from this hydrogen.

NADP (nicotinamide adenine dinucleotide phosphate)

A coenzyme that acts as an electron acceptor in photosynthesis.

Natural immunity

Immunity that occurs as part of the life of an organism. For example, the response of the immune system to a person contracting measles, or from antibodies crossing the placenta.

Natural killer (NK) cells

Cells that kill virus-infected cells and cancer cells. NK cells release chemicals called cytokines, which alert and attract other immune cells. A type of lymphocyte.

Natural killer T (NKT) cells

These cells have the characteristics of T cells and natural killer cells. NKT cells are involved in both the specific immune system and the non-specific immune system.

Natural selection

The preferential survival and reproduction of organisms better adapted to their environment.

Nausea

A feeling of sickness accompanied by the tendency to vomit.

Necrosis

The death of some or all cells in a tissue or organ through disease or injury, often causing an inflammatory response.

Neural tube

The precursor to the central nervous system in vertebrates. Neural tube defects such as spina bifida occur when the tube does not develop properly. Taking folic acid is important in reducing the risk of these defects.

Neurodegeneration

An umbrella term used to describe a range of conditions that affect the neurons of the brain. This includes Alzheimer’s, Parkinson’s and motor neurone disease.

Neurogenesis

The process of growth and/or development of neurons and related tissue.

Neuromuscular junction

The synapse between a skeletal muscle and a neuron.

Neuron (or nerve cells)

Specialised cells that are able to transmit nerve impulses via a synapse.

Neurotransmitter

A chemical that neurons use to communicate with one another. There are many kinds, including serotonin, dopamine and noradrenaline.

Neutrophils

Fast-acting phagocytes that flock to the site of inflammation. A type of white blood cell.

Niche

The specific role and position an organism occupies within its ecosystem.

Nitrogen cycle

A set of processes in which nitrogen – in various states – moves between the atmosphere, soil and organisms. The flow of nitrogen through the cycle is largely driven by bacteria.

Nodes of Ranvier

Areas of the axon without myelin. The action potential (electrical signal) jumps rapidly from one node of Ranvier to the next, speeding up conduction.

Non-polar

Any molecule in which the bonding electrons are distributed relatively evenly. Non-polar molecules show little reactivity and do not dissolve in water (they are hydrophobic). The fatty-acid ‘tails’ of phospholipids found in the lipid bilayer are non-polar.

Non-self

Anything that can be recognised as not belonging to the organism. When a non-self marker on a cell or particle is detected, the immune system launches an attack. Transplanted organs or blood can trigger such an attack.

Non-specific immune system (also innate immune system)

The first and second lines of defence against invading pathogens. It is short-lived and doesn’t involve any memory of previous infections. Found in all multicellular organisms. It includes barriers such as skin or plant cell walls, and processes like inflammation.

Noradrenaline

A neurotransmitter that influences emotions, sleeping and learning. It is also a hormone, and affects blood vessel contraction and heart rate.

Nuclear envelope

A double membrane that separates the contents of the nucleus from the cytoplasm.

Nuclear pores

Gaps in the nuclear envelope that allow substances to move in and out of the nucleus.

Nucleic acid

A polymer of nucleotides found in all living things. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are well-known examples.

Nucleolus

The part of the nucleus that produces ribosomes.

Nucleotide

A subunit of nucleic acids that includes a nitrogen base, a five-carbon sugar (ribose in the case of RNA and deoxyribose in the case of DNA) and one or more phosphate groups.

Nucleus

Where almost all the DNA is found.

Nucleus accumbens

A small region in the forebrain with ancient evolutionary origins, which helps regulate survival drives like food and thirst.

Nutraceutical

A combination of the words ‘nutrition’ and ‘pharmaceutical’, this term describes foods or food products that are believed by some people to be medically beneficial, although opinion is divided as to whether they really are. Examples include margarines supplemented with processed plant esters (stanols), which claim to lower consumers’ cholesterol levels.