In cellular respiration, animals use oxygen (O2) to harvest energy from their food, giving off carbon dioxide (CO2) as a waste product. To maintain their metabolism, animals' circulatory and respiratory systems keep O2 flowing to body tissues and remove CO2 to prevent the poisoning of cells. Almost all vertebrates use a respiratory pigment called hemoglobin to aid in this process.

Electromagnets coils of wire paper clips picked up 10 3 15 6 20 9 25 12 ms. owens' class was studying magnets. ms. owens showed her students how to make an electromagnet using a nail, a d-cell battery, and plastic coated wire. the students wrapped the wire around the nail and then attached the ends to the battery. when they were finished, they tested their magnets by investigating how many paperclips their magnets could pick up. they also tested whether they could increase the strength of their electromagnets by using more coils of wire. they recorded the class average of their results in the data table seen here. ms. owens asked her students to graph their data in a line graph. how should the students label the x-axis on their line graph? a) size of battery b) number of paper clips c) number of coils of wire d) strength of electromagnet