1st 9 week Study Guide--Biology Explain the difference between a control and a variable. What is the difference between a control group and an experimental group? Make a Venn diagram or T-chart comparing and contrasting a theory vs. a law. What is homeostasis? Smallest unit of life is ?. List ALL of the properties of water and give a real world example of each one. Explain the difference between adhesion and cohesion of water molecules. Why are water molecules considered polar? The pH scale is 0-14. Know which numbers are acidic and which are basic. Which side contains H+ and which is OH-? What is the difference between an ionic and covalent bond? What are the types of bonds called that connect one water molecule to another water molecule?