Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes.
Sodium-potassium pumps help nerve cells establish a voltage across their what?

Modern members of the reptiles group live in many different habitats and are found on every continent except antarctica.
Modern members of what broad animal group live in many different habitats and are found on every continent except antarctica?

Vitamins are the organic compounds that the body needs in small amounts to function properly; humans need 13 different ones.
What are the organic compounds that the body needs in small amounts to function properly; humans need 13 different ones?