Answer:
In cells, some molecules can move down their concentration gradients by crossing the lipid portion of the membrane directly, while others must pass through membrane proteins in a process called facilitated diffusion.
Explanation:
<h2>Follow instagrm at --> mvnnyvibes</h2>
Some living thing's bodies are weaker than others. For the species to live, the strong ones of the species will not get sick, reproduce and create strong offspring. The weak will die out.