TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Volvox sphere has a distinct front and back end.

SOLUTION: What has a distinct front and back end?

PROBLEM: Seismologists originally measured the intensity of an earthquake with the mercalli scale.

SOLUTION: How did seismologists originally measure the intensity of an earthquake?

PROBLEM: Some types of minerals form balls called nodules.

SOLUTION:
Some types of minerals form balls called what?