Title: वैकल्पिक

Text: Passive transport moves material down its concentration gradient. It requires no energy input and stops once equilibrium is reached. However, some cells require a concentration gradient to be created and maintained. Other cells must take in or expel materials too large to fit through a membrane protein. When passive transport will not get the job done, cells resort to active transport, which requires energy in the form of ATP (adenosine triphosphate). प्रत्येक पराग्राफले परीक्षण हुनेछ।

Save test: यदि तपाईं यो टाइपिङ परीक्षणलाई साझा गर्न चाहानुहुन्छ भने यो प्रयोग गर्नुहोस् (केवल प्रमाणीकृत प्रयोगकर्ताहरूको लागि)।