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

[Q]: Smaller size of ring will a summer drought cause in a tree.
[A]: What size of ring will a summer drought cause in a tree?

[Q]: Phototaxis is the term for movement toward light.
[A]: What is the term for movement toward light?

[Q]: The active transport of ions across the membrane causes an electrical gradient to build up across the plasma membrane.
[A]:
The active transport of ions across the membrane causes an electrical gradient to build up across the what?