Q.How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
Start your 14-day free trial to unlock the full solution →Neutral solutes cross the plasma membrane by simple diffusion, moving down their concentration gradient with no energy input; polar molecules cannot pass through the non-polar lipid interior on their own and are instead ferried across by carrier proteins embedded in the membrane.
The plasma membrane is selectively permeable, letting some substances through easily while holding others back, and the reason lies in how the membrane is built. Its core is a bilayer of phospholipids whose non-polar (hydrophobic) tails point inward, creating an oily, non-polar zone in the middle of the membrane. Whether a molecule can cross by itself depends on how it gets along with this non-polar interior.
Neutral solutes. Neutral (non-charged) solutes cross the membrane by simple diffusion. They move along the concentration gradient — that is, from where they are more concentrated to where they are less concentrated — and this happens without any input of energy. It is therefore a form of passive transport. (Water crosses similarly by diffusion, a special case called osmosis.)
Can polar molecules do the same? No. Polar molecules do not mix well with the non-polar core of the lipid bilayer, so they cannot slip straight through the membrane the way neutral solutes do. The very feature that lets neutral solutes pass — a non-polar interior — is what blocks the polar ones. …
Unlock everything free for 14 days
- Full step-by-step solutions
- Concept-first explanations
- Methods, shortcuts & mistakes
- PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.