What is the difference between bicuspid valve and tricuspid valve?

The mitral valve is also called the bicuspid valve because it contains two leaflets or cusps. ... The tricuspid valve has three leaflets or cusps and is on the right side of the heart. It is between the right atrium and the right ventricle, and stops the backflow of blood between the two.

a compound light microscope is used to magnify objects in steps.  

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for a different answer set the answer would be because the oxygen in the water had depleted (apex)