Final answer:
When the percent change in insulin demanded for any price change is zero, the demand curve is considered perfectly inelastic and the price elasticity of demand is zero.
Step-by-step explanation:
The percent change in insulin demanded for any price change is zero. The demand curve for insulin is perfectly inelastic, and the price elasticity of demand is zero. This means that regardless of the price of insulin, the quantity demanded does not change. Such a situation represents one of the polar cases of elasticity, where a percentage change in price, no matter how large, results in no change in quantity demanded. Insulin serves as a critical and life-saving medication for individuals with diabetes, which may help explain why its demand is perfectly inelastic - patients need it regardless of the price.