An experiment was designed to investigate the effect of caffeine on the heartbeat of the fleas. 2 populations of water fleas were cultured. both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same of light, and had their temperature maintained at 20 degree c. every 2 hours, water fleas from both populations were selected and their heartbeats were monitored. the fleas of pop.. 1 had caffeine administered 5 min.. before their heartbeats were checked. the fleas pop.. was given nothing. match: 10. what part of the experiment was food? 11. what part of experiment was the heartbeat? 12. what part of experiment was the h2o temp.? 13. what part of the experiment was pop..2? 14. what part of experiment was caffeine? a. independent variable b. dependent variable c. constant d. control