Assessment and Qualifications Alliance (AQA) GCSE Biology Paper 1 Practice Exam

A catalyst plays a crucial role in chemical reactions by increasing the speed of the reaction without undergoing any permanent change itself. This means that while the catalyst facilitates the reaction, it can be recovered in its original form once the reaction is complete. This ability to remain unchanged allows it to be used repeatedly in multiple reaction cycles, making it highly efficient.

In the context of chemical reactions, catalysts work by lowering the activation energy needed for the reaction to proceed. This opens up alternative reaction pathways, enabling the reactants to convert into products more readily. By doing so, catalysts help in achieving the desired reaction rate without being consumed, which is essential in various industrial processes and biological systems.

The other options do not accurately describe the primary function of a catalyst. For instance, saying a catalyst becomes consumed in the reaction is incorrect since it can be reused. Likewise, a catalyst is not limited to being a solid substance; it can exist in various states, including gases and liquids. Although it is true that catalysts decrease the energy barrier for reactions, the key defining characteristic that distinguishes them is their ability to increase reaction speed while remaining unchanged.