1. Ch. 2 : “Chemistry of Life”
Directed Reading: “Energy and Chemical Reactions”

2. Short Answer 1. Why is energy important to living things?
Energy powers the chemical reactions in cells.
2. How does the energy in food become available to organisms?
The energy in food becomes available to organisms through chemical reactions.

3. Matching 3. energy: e. the ability to move or change matter
4. reversible reaction:
d. can proceed in the opposite direction
5. products:
a. ending materials in a chemical reaction

4. Matching
6. chemical reaction: c. chemical bonds between atoms are broken and new ones are formed 7. activation energy: b. energy needed to start a chemical reaction 8. reactants: f. beginning materials in a chemical reaction

5. Explain the difference.
9. energy-releasing reaction, energy-absorbing reaction
The reactants of an energy-releasing reaction contain more energy than the products. The reactants of an energy absorbing reaction contain less energy than the products.

6. Explain the difference.
10. reactants, products
Reactants are the starting materials for a chemical reaction. Products are the ending materials of a chemical reaction.

7. Define 11. What is a catalyst?
Catalysts are substances that reduce the activation energy needed for chemical reactions.
12. What is an enzyme?
Enzymes are substances that increase the speed of chemical reactions.

8. Fill in the blank.
13. A substance on which an enzyme acts is called a(n) ___.
substrate
14. Hydrogen ___ is a substrate of the enzyme catalase.
peroxide
15. A(n) ___ is the part of the enzyme into which the substrate fits.
active site