OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What are enzymes mainly used for in biological systems?

To decrease reaction rates
To act as energy sources
As biological catalysts to speed up reactions
To bind with substrates tightly

The correct answer is: As biological catalysts to speed up reactions

Enzymes play a crucial role in biological systems primarily as biological catalysts. This means they significantly speed up chemical reactions that occur within cells without being consumed in the process. Enzymes lower the activation energy required for reactions to occur, enabling essential biochemical processes—such as digestion, energy production, and DNA replication—to happen much more efficiently and at lower temperatures than would otherwise be possible. For example, in metabolic pathways, enzymes facilitate the conversion of substrates into products by providing an active site where these substrates can bind and undergo transformation. This not only increases the rate of reactions but also allows for the regulation of metabolic processes according to the needs of the organism. By creating specific conditions and reducing the energy barrier for reactions, enzymes ensure that vital biological reactions occur in a timely and controlled manner, which is essential for maintaining life functions.