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How are veins and arteries adapted to the transport of blood?

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 muscle ...
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Answered by Amélie L. • Biology tutor
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Describe the process of DNA replication

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 exposed...
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Answered by Helena N. • Biology tutor
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Describe the process of phagocytosis and how antigen presentation leads to antibody production (9 marks)

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 an...
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Answered by Caine R. • Biology tutor
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Tobacco smoke contains carbon monoxide. Explain how carbon monoxide affects a persons ability to exercise.

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 less...
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Answered by Hersh P. • Biology tutor
5302 Views

Explain how eutrophication can result in low oxygen levels in the water in the stream.

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 underwa...
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Answered by Nadia B. • Biology tutor
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