Which instrument is used to perform the temperature cycling required for PCR?

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

Answer: (D)

PCR relies on precise, programmable cycling of temperatures to denature DNA, allow primers to bind, and extend new DNA strands in each cycle. The instrument that makes this possible is a thermocycler, which can rapidly and reproducibly switch between temperatures in a predefined program and run many samples at once, often with a heated lid to prevent evaporation. A water bath provides only a single or few fixed temperatures, not the repeatable cycling required. An incubator keeps the sample at a constant temperature for growth, and a spectrophotometer measures optical properties rather than controlling reaction temperatures. So the thermocycler is the best choice because it delivers the exact, automated temperature changes needed for PCR cycles.