Question 5
Taking the blood circulatory system, which level of organization does the heart belong to?
The right answer is the one marked above.
The organ level. It is a structure built from several tissues, cardiac tissue among them, with the definite job of pumping blood.
The cardiac muscle cell is the cell level; cardiac tissue is the tissue level; the heart together with the blood vessels is the system level. The heart on its own is an organ.