Why can some animal cells transport materials against a concentration gradient?

Question

Why can some animal cells transport materials against a concentration gradient? Could animals survive without this capability? --- this is our research from our subject Zoology.

Answer 1

They have to use energy to do that--simple diffusion won't work AGAINST the concentration gradient, as you know.  One such mechanism is active transport.  If they didn't use methods to move materials where they need to, they'd be completely at the mercy of their environments.  Not practical even for most single-celled organisms.  Here's a link to a nice overview of how things cross cell membranes:  http://www.wiley.com/legacy/college/boye...