Which of the following is an organic catalyst that speeds up chemical reactions in biological systems?

An organic catalyst that speeds up chemical reactions in biological systems is an enzyme. Enzymes are specialized proteins that play a crucial role in facilitating biochemical reactions by lowering the activation energy required for the reactions to occur. This allows processes essential for life, such as digestion, metabolism, and DNA replication, to happen more efficiently and at lower temperatures than would be possible without these catalysts.

Enzymes are highly specific, often acting on a particular substrate to produce specific products. They achieve their catalytic function by binding to the substrate and stabilizing the transition state, which leads to a faster conversion of substrates into products.

In contrast, while proteins can be enzymes, not all proteins function as catalysts. Lipids and carbohydrates perform different essential functions in biological systems, such as energy storage and structural roles, but they do not catalyze reactions like enzymes do. Thus, the correct answer highlights the unique role of enzymes in accelerating biological chemical reactions.