What are substances designed to speed up the rate of specific biochemical reactions called?

Substances that are designed to accelerate the rate of specific biochemical reactions are known as enzymes. Enzymes are proteins that act as catalysts in various biochemical processes, facilitating reactions that are essential for life. They lower the activation energy needed for a reaction to occur, significantly speeding up metabolic pathways. Each enzyme is specific to a particular substrate and reaction, which is crucial for maintaining the efficiency and regulation of cellular functions.

Hormones, on the other hand, are signaling molecules that regulate physiological activities but do not directly catalyze biochemical reactions. Receptors are proteins that receive and transmit signals, typically from hormones or neurotransmitters, but do not facilitate reactions themselves. Neurotransmitters are chemicals that transmit signals across synapses in the nervous system, influencing various functions but not acting as catalysts in biochemical reactions. Hence, enzymes are specifically designed for this role, making the selection of that answer accurate.