Determine approximately how much total energy is passed to the tertiary consumers if 1000 calories enter at the autotroph level

Correct 1 calorie.

By definition, the amount of energy that passes from a lower level to the next higher level on a food chain is about 10% of that that was at that level. So, if there are 1000 calories in an autotroph level, the next level, primary consumers, will get 100 calories from it, the secondary consumers, 10 calories, and the tertiary consumers, 1 calorie.