Question

1. your friend says that energy is \used up\ between each trophic level so the total amount of energy decreases. is he correct?

yes, the energy disappears between each trophic level and no longer exists after being used by organisms.
no, the energy increases as it moves up the trophic levels because organisms gain more energy from their food.
yes, the energy is completely used up by organisms and no longer exists at higher levels.
no, the energy is used by organisms but not lost—it changes forms and is released as heat.

Explanation:

According to the law of conservation of energy, energy cannot be created or destroyed, only transformed. In a food chain, energy is transferred between trophic levels. Organisms use energy for various life processes (such as metabolism, movement, etc.), and some of this energy is lost as heat (due to inefficiencies in energy transfer, like during cellular respiration). So, energy is not "used up" in the sense of disappearing completely.

Answer:

No, the energy is used by organisms but not lost—it changes forms and is released as heat.