In an experiment comparing glucose-containing and glucose-free culture media, bacterial colonies appear only on the glucose-containing media. Which concept does this illustrate?

• A. Movement
• B. Stimuli
• C. Adapt
• D. Energy

Answer: (D)

Energy availability drives growth. Bacteria must have a source of energy to power metabolism and replication. Glucose provides an easy energy source; when it’s present, cells can metabolize it to generate ATP, fueling the synthesis of new cellular components and division, which leads to visible colonies. Without glucose, there’s no readily usable energy for these processes, so growth stops and colonies don’t form. This isn’t about movement toward glucose, signaling responses, or a genetic adaptation—it's about having the energy needed for growth in that environment.