Cell membranes (plasma membranes) organisms maintain homeostasis by controlling what substances may enter or leave cells. some substances can cross a cell membrane through passive transport, while other substances can only cross a cell membrane through active transport. what is the difference between active and passive cellular transport?

Active transport requires energy and moves materials from a place of low concentration to a place of higher concentration. Passive transport does not require energy and moves material from high concentration to lower concentration.

Well first you need to know that passive transport moves molecules with the concentration gradient  which is high to low, while the active transport moves molecules against the concentration gradient which is low to high. Also, passive transport doesn't require energy which is ATP, while active transport does require energy.

Hoped I helped! I LOVE biology so if you need any help with cells, human systems, etc I'm your gal! :)