A system is contained by its boundary; therefore, the size of a system is limited by its boundary.
A simple example is a connection between the circulatory and respiratory systems. <span>As </span>blood<span> circulates through your body, it eventually needs fresh oxygen </span><span>from the air. When the </span>blood<span> reaches the lungs, part of the </span>respiratory system<span>, the </span>blood<span> is re-oxygenated.</span>
The sun gives the animals energy to do whatever they want
