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The cardiac cycle is the continual sequence of contraction and relaxation of the atria and ventricles to keep blood continually circulating around the body.

First the atria contract decreasing thei...

Arteries carry blood away from the heart to the rest of the body and veins then take blood back to the heart. Because the heart directly pumps blood into the arteries by its forceful contractions, arterie...

Sometimes, a chance mutation in bacterial DNA allows certain bacteria to become resistant to certain types of antibiotic. When an antibiotic is given, only the non-resistant strains of bacteria will be ki...

Firstly, although fetal haemoglobin is better at binding oxygen, it is also worse at giving up oxygen to the tissues which need it. Secondly, if adults had haemoglobin with the same affinity for oxygen as...

The first stage in viral replication occurs when a virus attaches to the surface of a host cell. The viral nucleic acid (VNA) then enters the cell. The VNA then takes over the cell, altering the metabolis...