Structures that allow for one-way blood flow through the heart.

The heart is primarily made of a thick muscle layer, called the myocardium, surrounded by membranes. One-way valves separate the four chambers. After blood passes through the pulmonary arteries, the right semi lunar valves close preventing the blood from flowing backwards into the right ventricle.

the answer is z.

the human body has five levels of organization. level 1: cells. cells are the basic units of life and form the first level of organization. cells in the human body have specific functions. examples include nerve cells, blood cells, liver cells, and so on.