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
IgA

A type of immunoglobulin, or antibody, that is important at the sticky mucosal surfaces where many pathogens try to enter the body, such as in the intestines.

IgD

A type of immunoglobulin, or antibody, that is found on the plasma membrane of immature B cells and also secreted in the blood. Its role is not yet clear.

IgE

A type of immunoglobulin, or antibody, that binds to allergens and mast cells, triggering the release of histamine. It plays a role in various allergic diseases, including food allergies and asthma, and in immunity to certain parasites, including some kinds of worms and the parasite that causes malaria in humans.

IgG

The most abundant immunoglobulin, or antibody, in the blood serum of humans. It plays an important role in the humoral response of the specific immune system. It is the only type of immunoglobulin that crosses the placenta.

IgM

A type of immunoglobulin, or antibody, that exists mostly as a pentamer (five monomers joined together). It is the first immunoglobulin to be made by a B cell when it is exposed to an antigen.

Immune system

This helps a living thing defend itself against infectious organisms and other foreign substances. In mammals, it includes the non-specific (innate) immune system and the specific (adaptive) immune system.

Immunoglobulin (Ig)

Also known as an antibody. This is a Y-shaped globular protein, whose secondary structure is based mostly on beta-pleated sheets. It is produced by plasma B cells to fight against antigens. Types include IgA, IgD, IgE, IgG and IgM.

In vitro fertilisation (IVF)

A procedure in which an egg and sperm are joined in a test-tube to form a zygote, which can then be implanted into a uterus to grow.

Inflammation

When the receptors of cells involved in the non-specific immune system are engaged by pathogens, the cells release molecules that trigger inflammation. Inflammation causes increased blood flow to the area, which leads to swelling, pain and an increase in temperature.

Influenza A(H1N1)pdm09

The name of the virus responsible for the 2009 influenza pandemic. For a while, ‘S-OIV’ (swine-origin influenza virus) was used, but ‘influenza A(H1N1)pdm09​’ virus is now its official WHO-approved name.

Inhibitor

A compound, such as a drug, that can prevent an enzyme or other biomolecule from functioning.

Inhibitory neurotransmitter

Neurotransmitters that decrease the likelihood that the receiving neuron will produce an action potential.

Innate immune system (also non-specific 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.

Inorganic phosphate (Pi)

A molecule that plays a key role in respiration and photosynthesis and which, among its functions, combines with ADP to create ATP.

Insoluble fibre

A necessary part of our diet, found in whole grains and vegetables. Insoluble fibre helps speed the transit of food through the intestines and adds bulk to stools.

Insulin

A hormone secreted by the pancreas that regulates blood glucose levels. When blood glucose levels are high, insulin causes glucose to be stored as glycogen in the liver and muscles.

Integral membrane protein

A protein that is permanently anchored within the plasma membrane.

Integrin

A group of membrane molecules involved in cell–cell binding.

Intermediate filaments

Cytoskeleton components that are made of numerous proteins, involved in providing structure and strength to the cytoskeleton.

Ion

An atom or molecule that has lost or gained electrons to become either negatively or positively charged.

Ion channel

A protein or assembly of several proteins in the cell membrane that opens and closes to let ions move in and out of cells.

Ionising radiation

Radiation that has so much energy that it can remove electrons from an atom’s orbit when it comes into contact with it, ‘ionising’ or charging it. These type of radiation – which include X-rays, gamma rays and cosmic rays – are often harmful to humans, causing DNA mutations or cell death.

Isomer

A compound which has the same formula as another, but with different properties due to an alternative arrangement of atoms.