Science essay.."Explain how our circulatory and respiratory systems respond to exercise."?

Ok i have a science essay of which that is due tomorrow, The question is "Explain how our circulatory systems respond to exercise." ..we have to include What are the respiratory and circulatory systems used for and what do they do ? .. what exercise is? and anything else you think will be very helpfull! thankyou for helping and i will be voting for best answer so make sure your answers are relevant and have usefull information i may use :) Ps: if i dont do this then i wont get to dissect a heart! :( so please help! ..Thanks a million. )