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
Leptin

A hormone, produced by adipose tissue, involved in the regulation of hunger. Leptin acts on the hypothalamus in the brain, inhibiting appetite by counteracting the effects of other hormones.

Leucocytes (also leukocytes or white blood cells)

Made in the bone marrow, these cells are an important part of the immune system. There are two main types: granulocytes, which have granular cytoplasm and a lobed nucleus, and agranulocytes, which have smooth cytoplasm and a non-lobed nucleus.

Light-dependent reactions

The first stage of photosynthesis. These reactions take place in the thylakoid membrane, forming an electron transport chain that creates ATP and reduced NADP.

Light-independent reactions

Also known as the Calvin cycle, these three reactions – carbon fixation, reduction and regeneration of ribulose bisphosphate (RuPB) – form the second stage of photosynthesis, in which glucose is produced. They occur in the chloroplast stroma.

Limbic system

A set of structures sitting above the brainstem that are involved in emotion, motivation and memory. They include the hypothalamus, the amygdala and the hippocampus.

A step in the process of aerobic respiration that removes hydrogen and carbon dioxide from pyruvate to form acetyl CoA. This process occurs in the mitochondrial matrix.

Lipase

A type of enzyme that breaks down lipids, including dietary fats and fat stored in our bodies as triglycerides, into glycerol and fatty acids. Lipases cause hydrolysis, the process where the bonds between glycerol and fatty acids are broken using water molecules.

Lipid

The chemical name for fats and other related compounds. The high energy value of lipids makes them an important food type that all organisms need. They form part of the membranes that protect cells from their surroundings. Lipids dissolve in ethanol, but not in water.

Lipid bilayer

A cell membrane consisting of two layers of lipid molecules.

Lipoproteins

A soluble group of proteins which transport fat (or other lipids) in the blood plasma. The two main types are high-density and low-density lipoproteins.

Logarithmic scale

A nonlinear scale based on orders of magnitude (101, 102, 103 and so on) often used for plotting data when there is a large range of quantities that would otherwise be difficult to visualise.

Longitudinal studies

Studies examining the same group of individuals at regular intervals.

Lorenzo’s oil

A proposed treatment for a condition called adrenoleukodystrophy (ALD). It is prepared from olive oil and rapeseed oil, and consists of four parts glyceryl trioleate and one part glyceryl trierucate.

Low-density lipoprotein (LDL) cholesterol

Cholesterol is transported in the blood in complexes called lipoproteins. High-density lipoproteins (HDLs) tend to remove cholesterol from the tissues to the liver for excretion. Low-density lipoproteins (LDLs) are more likely to deposit cholesterol in damaged areas of blood vessels and lead to the formation of atherosclerotic plaques. High levels of LDL cholesterol can lead to heart disease, whereas high levels of HDL cholesterol can protect against heart disease.

Lymphocytes

Agranulocyte white blood cells. Types include B cells, T cells and natural killer cells.

Lysosomes

Membrane-bound organelles that are the cell’s rubbish disposal and recycling units. They contain hydrolytic enzymes.