2. Mechanisms, Data, and Fair Tests

Harder science questions reward thinking about how and why, and reading evidence carefully.

• Trace the process. Know the inputs and outputs of photosynthesis and respiration, and how energy and matter move through a system.
• Read every axis. On a graph, check the title, the labels, the units, and the trend before you answer.
• Independent vs. dependent variable. The independent variable is what you change; the dependent variable is what you measure in response.
• Conservation. Atoms are rearranged but not created or destroyed; energy changes form but the total is conserved.