Which tube shows no enzyme activity despite having oil and bile salts?

• A. Tube 2
• B. Tube 3
• C. Tube 1
• D. Tube 4

Answer: (D)

The key idea is that fat digestion by lipase needs the enzyme itself in addition to the oil substrate. Bile salts don’t hydrolyze fats; they emulsify the oil to increase the surface area available for lipase. So, if a tube contains oil and bile salts but no lipase, there will be no triglyceride breakdown and no fatty acid production, regardless of the emulsification. That tube shows no enzyme activity because the essential catalyst (lipase) is missing. The other tubes either contain lipase (and thus show activity by converting triglycerides into fatty acids and glycerol) or have conditions where the enzyme can act, but without the enzyme being present, activity cannot occur.