What disappears entirely in the deep ocean? ?

Light disappears entirely. Sunlight is unable to penetrate that deep, which is why many fish have adapted to produce their own light.

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.