"explain how and why de-oxygenated blood is pumped to the lungs and is then returned to the heart were the blood now rich with oxygen is pumped throughout the body. make sure to include both atrium and ventricles of the heart in your answer."

Heart and lungs:

The upper chamber of the heart is called atrium and lower chamber of the heart is called ventricles.

The blood circulation in the heart is basically under the functioning of three blood vessels namely:

Arteries: They start with the aorta, the huge vein leaving the heart. Veins divert oxygen-rich blood from the heart to the majority of the body's tissues. They branch a few times, decreasing and littler as they convey blood more remote from the heart. Capillaries: These are little; flimsy blood vessels that associate the arteries and the veins.Their dainty dividers permit oxygen, supplements, carbon dioxide, and other waste items to go to and from our organ's cells. Veins: These are the blood vessels that return blood to the heart; this blood needs (oxygen-poor) and is wealthy in waste items that are to be discharged or expelled from the body.Veins become bigger and bigger as they draw nearer to the heart.The unrivaled vena cava is the huge vein that brings blood from the head and arms to the heart, and the second rate vena cava brings blood from the mid-region and legs into the heart.

The answer your looking for is a food chain grid. it describes how nature can support itself and survival of the fittest comes into play..