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

Enzymes are considered biological catalysts primarily because they speed up biochemical reactions in the body. These proteins are essential for facilitating various chemical processes that occur within living organisms. In numerous metabolic pathways, enzymes lower the activation energy required for reactions to proceed, enabling them to occur quickly and efficiently at the temperatures typical of living organisms.

This catalytic function is vital because many biochemical reactions, if they occurred without the presence of enzymes, would happen too slowly to support life. Therefore, the presence of enzymes is crucial for maintaining the rates of metabolic reactions that allow organisms to grow, reproduce, and respond to their environments.

While enzymes do exhibit certain characteristics such as being able to work for extended periods without being consumed in reactions, and they can be affected by temperature, those factors alone do not define their role as biological catalysts. Their primary function remains centered on accelerating reactions, which is what makes answer B the most accurate description of enzymes.