When bacteria swim from cold to warm regions, this is known as

Step 1: Analyze the question The question asks for the name of the response in which bacteria move from a cold region toward a warm region. The key word is temperature.

Step 2: Explain the concept A taxis is a directional movement of a whole organism in response to a stimulus. The prefix tells you the type of stimulus, and positive or negative tells you the direction:

• Phototaxis: response to light
• Chemotaxis: response to chemicals
• Thermotaxis: response to temperature
• Positive: movement toward the stimulus
• Negative: movement away from the stimulus

Step 3: Work through the options

• A. Positive phototaxis: movement toward light. Light is not involved here, so this is wrong.
• B. Negative phototaxis: movement away from light. This is also wrong.
• C. Positive thermotaxis: movement toward a warmer region. The stimulus is temperature and the bacteria move toward the warmth, so this fits.
• D. Negative chemotaxis: movement away from a chemical. No chemical is mentioned, so this is wrong.

Step 4: Answer Bacteria moving from a cold region to a warm region are showing positive thermotaxis.

Exam tip: Break each term into two parts, stimulus + direction. Thermo = heat, photo = light, chemo = chemicals. Positive means toward and negative means away. Then match the stimulus in the question to the correct prefix.