Which device controls temperature cycling during PCR?

• A. Water bath
• B. Incubator
• C. Thermocycler
• D. Spectrophotometer

Answer: (C)

PCR relies on precise, programmable temperature cycling to denature DNA, allow primer annealing, and extend new strands. The device designed for this is a thermocycler. It can be programmed with exact temperatures and times for each step and automatically cycles through them, enabling rapid and repeatable heating and cooling of the reaction mix. It uses Peltier elements to switch temperatures quickly and a sensor to monitor the sample temperature, often with a heated lid to prevent condensation. The other instruments have steady-state purposes: a water bath holds a single temperature, an incubator maintains a constant temperature for growth, and a spectrophotometer measures absorbance rather than cycling temperatures.