Question concerning water?

Question

"At the beginning of winter, a friend suggests skating on a large local pond. Explain, using scientific reasoning, the need to be cautious about the thickness of the ice."

I HAVE THAT PART ^^^
The way water freezes from top to bottom.

It's this part I need help with:

"Identify two biological processes that depend on the same principle."

Answer 1

When water freezes it expands so it is lighter than water and will float.