Q: A teacher demonstrates a chemical reaction. A student observes that the test tube in which the reaction occurs becomes warm. What is the source of the thermal energy generated by the reaction?
A: energy stored in the reactants
Q: Which system supports the body, protects internal organs, and makes blood cells?
A: skeletal system
Q: Which system absorbs and carries food from the digestive system to the rest of the body?
A: circulatory system
Q: Index fossils help scientists estimate the age of a rock because index fossil species only existed for a relatively short time. What happened to the species that are now used as index fossils?
A:
They became extinct.