Final answer:
A straight up demand curve represents Perfectly Inelastic demand, indicating that quantity demanded isn't affected by price changes, unlike a constant unitary elasticity demand curve which is curved and shows proportional changes in price and quantity.
Step-by-step explanation:
When a demand curve is represented by a straight line going straight up, it indicates that the quantity demanded does not change despite changes in price.
This scenario is classified as Perfectly Inelastic demand, which means that consumers' demand for a good does not respond to price changes.
The correct answer to the question is 'A) Perfectly Inelastic.' This is different from unitary elasticity, where a constant unitary elasticity demand curve would demonstrate proportional changes in price and quantity demanded and would be a curved line, not a straight up-and-down line.