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Artery walls are made up of smooth muscle tissue and a thick elastic layer which allows them to expand and contract easily, coping with the changes in blood volume that occur with each heartbeat. The musc...

In DNA replication, first the hydrogen bonds between the nitrogenous bases are broken catalysed by the enzyme helicase, causing the DNA double helix to unwind and unzip, leaving the nitrogenous bases expo...

White cell (macrophage/neutrophil) detects bacteria antigen by binding to cell surface receptorsWhite cell engulfs bacteria (this is endocytosis), bacteria is held in a phagosome Lysosomes enter phagosome...

Carbon monoxide is a poisonous gas. It binds to haemoglobin in red blood cells irreversibly. This means that less oxygen can be carried by red blood cells. As oxygen delivery decreases to muscles and so l...

Eutrophication occurs when excess nitrates from fertilisers seep into the stream. The nitrates cause algal bloom on the surface of the water. As a result, sunlight is blocked from reaching the plants unde...