The heart must beat faster during exersise because by increasing the heart rate the body is able to increase cardiac output and deliver the necessary blood flow to the mucles
When animals undergo the process of cellular respiration, they release carbon dioxide into the atmosphere. And when animals die and start to decay aided by organisms called decomposers, carbon dioxide is also emitted into the atmosphere. When humans burn fossil fuels, carbon dioxide yet again enters the atmosphere.
<em>hope this helps ;)</em>
Gene is the correct answer