Which of the following contributions to the theory of the conservation of energy is an observation of a biological system?
a. julius von mayer’s observation that vibration increases the temperature of water
b. james prescott joule’s observation that the potential energy of a weight can be converted into heat energy
c. hermann von helmholtz’s demonstrations that energy is converted but not created when animal muscles move
d. baron kelvin’s hypothesis that the melting point of ice decreases as pressure decreases

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.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.