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


Palm oil

A vegetable oil obtained from the fruit of the oil palm, mostly the African oil palm Elaeis guineensis. It is used as a fat in many different foodstuffs and cosmetics.


A large-scale epidemic affecting many countries.


A type of interaction between species (symbiosis) in which one species (the parasite) benefits at the expense of the other species (the host).

Parietal lobe

The part of the brain that processes information from the body and senses, and integrates it to help orient the body and carry out movement in space.

Parkinson’s disease

A neurodegenerative disease caused by a loss of nerve cells in a part of the brain called the substantia nigra, leading to a reduction in the amount of dopamine in the brain.

Passive immunity

Immunity that comes from antibodies from outside of the organism – for example, those made in the laboratory, or those that cross the placenta between a pregnant woman and a fetus. Short-lived, as memory cells are not made.


A disease-causing organism.


Short chains of amino acid molecules that join together, via peptide bonds, to create proteins.


A protein that causes cells to lyse (burst) by causing pores to form in their plasma membrane. Found in the granules of natural killer cells and cytotoxic T cells.

Peripheral membrane protein

A protein that temporarily associates with the membrane, either directly with lipids or with integral membrane proteins.

Peripheral nervous system (PNS)

Any part of the nervous system outside of the brain and spinal cord. The PNS connects the central nervous system (CNS) to different parts of the body, enabling the CNS to control them.

Peroxisomal membrane

Membrane of a cytoplasmic organelle specialised for carrying out oxidative reactions.


Cells that are capable of engulfing and absorbing materials including waste products, microorganisms and foreign bodies.


When a living cell engulfs another cell, bacterium or other particle. Performed by phagocytes such as macrophages, neutrophils and eosinophils.

Pharmaceutical company

A large company researching and making new drugs (collectively often called ‘pharma’).


A genetic engineering technique in which genes are modified (or inserted) in cells to make them produce pharmaceuticals.


The physical traits of an individual (eg having red hair), which are dependent on an individual’s genotype and interactions with their environment. Compare with genotype.


Also known as PKU, this is a genetic disorder in which the enzyme responsible for metabolising the essential amino acid phenylalanine into tyrosine is inactive. This leads to a build-up of phenylalanine, which can cause brain damage. Sufferers need to eat a very strict low-protein diet to prevent excess phenylalanine being consumed.


A type of lipid with a hydrophilic head made of a glycerol molecule and phosphate group, and two hydrophobic fatty-acid tails. Biological membranes contain a double layer of phospholipid molecules, called the lipid bilayer.


The process of a phosphate group being added to a molecule.


A chemical reaction in which a compound is broken down using light energy. Photosystem II uses water photolysis to replace the electrons emitted from its reaction centre.


The process used by green plants and some other organisms to form nutrients from carbon dioxide and water, using sunlight as an energy source.

Photosystem I (PSI)

The second photosystem in the electron transport chain of the light-dependent reactions of photosynthesis (but named because it was discovered first).

Photosystem II (PSII)

The first photosystem in the electron transport chain of the light-dependent reactions of photosynthesis (but named because it was discovered second). It uses light energy to emit excited electrons sourced via photolysis of water.


Movement or growth in plants in response to light.


Chemicals that occur naturally in plants, such as stanols, sterols, polyphenols and carotenoids.


Microscopic photosynthesising organisms that live in the upper, sunlit areas of bodies of water.

Pituitary gland

The ‘master gland’ of the body, which releases hormones that control growth, blood pressure, the stress response and the function of the sex organs.


A dummy treatment used during clinical trials.

Planar polarity

Planar cell polarity refers to the spatial organisation of cells, which often allows them to carry out specialised functions.

Plant growth factors

The name given to the hormones in plants that control growth and development, such as auxins, cytokinins, gibberellins, ethane and abscisic acid.

Plant sterols

Natural steroid compounds found in plants that are thought to work in several ways, including by lowering cholesterol absorption by the gut. They can be consumed in fruit, vegetables and other plant foods, but people with high cholesterol sometimes consume fortified spreads, yoghurts and milk as well.


Made up of fats and cholesterol as well as calcium and blood clotting agents, plaques are lesions in the arterial wall which can cause obstruction, resulting in increased blood pressure and cardiovascular disorders such as atherosclerosis.

Plasma B cells

B cells that have been activated to produce antibodies. One B cell makes only one type of antibody. A type of lymphocyte.

Plasma membrane

A phospholipid bilayer that contains cholesterol and proteins. It surrounds the cell and enables it to communicate with its neighbours and detect and respond to changes in the environment.


A cell junction involved in connecting the endoplasmic reticula of two plant cells, allowing direct communication.


The ability to give rise to all cell types of the body (but not placental cells).


Any molecule that has a partial positive charge at one side and a partial negative charge at the other. Polar molecules react with water (they are hydrophilic). The glycerol and phosphate heads of the phospholipids found in the lipid bilayer are polar.


Phytochemicals made up of multiple phenol groups. They are responsible for a wide range of plant functions, including growth, reproduction, pigmentation and resistance to pathogens.


The presence of multiple sets of chromosomes in a cell.


Carbohydrates consisting of long chains of sugar molecules.

Polyunsaturated fats

Fat molecules that contain two or more double bonds between their carbon atoms.


All the members of a single species living together in the same location or habitat.

Population genetics

The study of the genes of a population, including both the frequency and interaction of genes and their variants (their alleles).

Positive selection

Selection of alleles that are likely to have provided an advantage to organisms.

Postdoctoral (postdoc)

A label used to describe the period after a doctorate, and often used to describe a paid research job someone can do after completing a PhD. Both the positions and the people that do them can be called postdocs.

Postgraduate qualifications

Qualifications that require someone to have a Bachelor’s degree. They include postgraduate certificates, postgraduate diplomas, Master’s degrees and doctorates.


A chemical compound that precedes another in a series of chemical reactions. L-DOPA is the precursor of dopamine and noradrenaline, and cholesterol is a precursor of bile acids and steroid hormones.

Prefrontal cortex

A part of the frontal lobe of the brain that is involved in many cognitive functions, including memory, language, planning and decision making.

Primary structure

The amino acids that make up a protein or polypeptide chain, linked by peptide bonds.


A single-celled organisms that lacks any membrane-bound organelles. Prokaryotic organisms include two domains of life, bacteria and archaea.


Rapid multiplication of similar types of cell.

Promoter DNA

A region of DNA that initiates transcription of a particular gene.

Prospective studies

Studies that look forward in time.


A large molecule, made of amino acids, that is encoded by a gene or genes and that performs a specialised job in the cell.


Proteins bound to polysaccharide groups, often found in connective tissue.


A type of eukaryotic and (usually) unicellular microscopic organism. Once a very broad classification, today the term refers to protozoans, unicellular algae and simple fungi.


A type of unicellular eukaryotic organism. An example is Plasmodium falciparum, which causes malaria in humans.


A disrupted, usually non-functional version of a gene.


The period during which humans reach sexual maturity.


An organic acid that is the end product of glycolysis, the first step in cellular respiration.