ばならないmust...ばかりonly; justばいいshould...ばいいのにwould be nice if...ばおもいだす思い出すto remember; to recall (when... is mentioned)ばかりかnot only... but also...なければif not; unlessたらきごう/ればif...ばかりでなくnot only... but also... (alternative form)よければif you'd like...ればこそprecisely because...
To survive, the polar bear must keep its body at the right temperature and store enough energy to last between meals that could be a few days or a few months apart.