Advanced Placement (AP) Biology Practice Exam

What is a catalyst?

1. A substance that increases the temperature of a reaction

2. A chemical agent that changes the rate of a reaction without being consumed

3. A reactant that participates in every reaction

4. An enzyme that speeds up all reactions

The correct answer is: A chemical agent that changes the rate of a reaction without being consumed

A catalyst is defined as a chemical agent that changes the rate of a reaction without being consumed in the process. This means that a catalyst can facilitate a chemical reaction by lowering the activation energy required for the reaction to proceed, allowing the reaction to occur more quickly or under milder conditions. After the reaction, the catalyst remains unchanged and can be used repeatedly for the same reaction. The ability of a catalyst to remain unchanged makes it a crucial component in many biological and industrial processes where efficiency is critical. For instance, in biological systems, enzymes are specific types of catalysts that speed up biochemical reactions essential for life, but not all catalysts are enzymes, and they do not necessarily speed up every reaction. In contrast, the other options do not accurately reflect the definition of a catalyst. A catalyst does not inherently change the temperature of a reaction, nor does it participate in every reaction or speed up all reactions universally, as some reactions may require different types of catalysts depending on the conditions and substrates involved. This highlights the specialized function of catalysts in various chemical and biological contexts.