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
GABA (gamma-aminobutyric acid)

The main inhibitory neurotransmitter in the brain.

Gap junction

A cell junction involved in connecting the cytoplasm of two animal cells to allow direct communication.

GDP (guanosine diphosphate)

A molecule converted to GTP during the Krebs cycle.

Gene

The fundamental unit of inheritance. Genes are lengths of DNA, and most contain information for making proteins.

Gene expression

When a protein is made from the information on a gene.

Genetic code

The order of the chemical units of DNA (bases) determines the order of the chemical units of proteins (amino acids). There are 64 three-letter ‘words’ in the code.

Genetic drift

Random changes in the frequency of alleles in a population, not linked to selection pressures.

Genetics

1. The study of the structure and function of genes.
2. The genetic features that occur in individuals, families and populations.

Genome

The complete genetic information of an organism, found in nearly every type of cell.

Genotype

The genetic characteristics of an individual (eg having the gene or genes for red hair). Compare with phenotype.

Gestation

The period during which a fetus develops inside the uterus (ie pregnancy).

Ghrelin

A hormone produced by cells in the stomach lining and pancreas. Ghrelin stimulates hunger, increasing food intake, and is also important for the secretion of growth hormone.

Gibberellins

A group of plant growth factors/hormones that control stem elongation between leaves, seed germination and fruit growth.

Glial cells

Non-neuronal cells found in the brain and other parts of the nervous system. Their roles include supporting neurons and forming the myelin sheath.

Glucose

A hexose sugar and the product of photosynthesis. It is one of the main sources of chemical energy used in cellular respiration. Animals get glucose from the food they eat; plants create it via photosynthesis.

Glutamate

The brain’s main excitatory neurotransmitter. It is also the precursor to GABA (gamma-aminobutyric acid).

Glycerol

An odourless liquid that can be used as a solvent, antifreeze, pharmaceutical ingredient and sweetener (known as E422). The condensation of one glycerol molecule with three fatty acid molecules produces one triglyceride molecule – which we use to store fats in the body – and three water molecules.

Glycogen

A branched polymer of glucose that acts as a long-term energy store for animal cells.

Glycolipid

A lipid with carbohydrate attached.

Glycolysis

The splitting of sugar. This process, in which glucose is oxidised and converted to pyruvate, takes place in the cytoplasm. It is the first stage of both aerobic and anaerobic respiration.

Glycoproteins

Proteins with covalently attached sugar units.

Glycosidic bonds

Covalent bonds that link sugar molecules to other molecules, including other sugars.

GM (genetic modification)

The practice of altering an organism’s genome, either by modifying its genes or transferring in genes from another organism.

Golgi apparatus

An organelle and one of the wondrously complex membrane systems in the cytoplasm, which modifies, packages and directs newly made proteins to where they are needed.

Graduate

Relating to someone who has completed a university degree, usually a Bachelor’s degree. Many employers offer graduate training schemes.

Gravitropism

Movement or growth in plants in response to gravity.

Gravity

The force of acceleration of one object towards another. Gravity holds humans to the earth and keeps the Earth in orbit around the sun. Gravity on Earth – normal gravity or G – is equal to 9.8 ms-2.

Greenhouse gases

Atmospheric gases that trap heat. The most important are:

  • water vapour (has the biggest greenhouse effect, but levels are relatively stable)
  • carbon dioxide (CO2)
  • methane (present at lower levels than carbon dioxide, but has a much stronger greenhouse effect)
  • lower-atmosphere ozone

Other chemicals, such as nitrous oxide and CFCs (chlorofluorocarbons), are also greenhouse gases, but are present at low levels.

GTP (guanosine triphosphate)

A molecule produced during the Krebs cycle that donates a phosphate group to ADP to make ATP. It is also very important elsewhere in the cell.

Guard cells

Specialised cells on the outside layer (epidermis) of plant leaves that open and close stomata to control gas exchange and water loss.