Why does your pulse rate increase as your level of activity increases?

Please answer quick!

Would really appreciate it, i have an idea but not completely sure

Which statement correctly describes a way that mutations increase the likelihood that a species will survive in a changing environment

Students in biology are studying the macromolecules of life. they used a calorimeter to determine the calories in various types of food. once the lab was completed, the students ate the left over food samples. monica commented that in just 6 or 7 "chews" of the saltine, it was gone; nothing but a sticky paste in her mouth. elaborate on what happened chemically while chewing the saltine. include the macromolecules present.