Here are the answers to your questions:
Question 1: The molecule that is broken down during cellular respiration is sugar.
Question 2: When pyruvic acid is created during cellular respiration, in addition to the four total ATP produced, heat is also produced as a result of this reaction.
Question 3: Hydrogen bonds tightly to oxygen during cellular respiration because it is less electronegative than oxygen.
Question 4: The byproduct of lactic acid fermentation is lactic acid.
Question 5: When a reaction releases more energy than it uses, it is called exothermic.