Cotransport works by the movement of one molecule across a membrane from an area of lower concentration to an area of higher concentration because at the same time

Question

Cotransport works by the movement of one molecule across a membrane from an area of lower concentration to an area of higher concentration because at the same time

Question 31 options:

a	a H+ ion moves up its concentration gradient and increases the membrane potential
b	a H+ ion moves down its concentration gradient and increases the membrane potential
c	a H+ ion moves down its concentration gradient and decreases the membrane potential
d	a H+ ion is not required.

Answer 1

The answer to this question is B. & I'll explain:

Imagine, for a second, that you pour a whole gallon of water right in the center of a table. In the first couple of second, the water has a REALLY high concentration at its center (Because you poured it there), & it has a very low concentration on the edges of the table (Because it hasn't spread there yet). After a couple of seconds this water will spread out, also called diffuse, to the edges of the table. Any object that was on the edge, say a pen, will now be pushed over the edge along with the water.

That's what happens in this process described in the question, which is called secondary active transport. Some molecule, in this case H+, is held in a high concentration, & because of that it wants to spread to the areas of low concentration. Other molecules can be pushed along, even if it means that they go from areas of low concentration to high concentration. Usually this low-to-high takes a lot of energy (ATP) to do, but in this case the energy comes from the H+ ions pushing other molecules.

I hope this answer helps you. If you liked my answer & explanations you should sign up for tutoring with me & I can help break down complex processes in cells into easy to understand ideas.

Kindly,

Michael

Answer 2

Hi Mocha,

Here's some info that should help!

Co-transport is when one molecule moves against its concentration gradient which is powered by a second molecule that moves with (or down) it's concentration gradient. While not always the case, H⁺ is often the powering molecule that moves down it's concentration gradient.

This leaves this B and C as possible answers.

In order for H⁺ to be able to move down it's concentration gradient, there must be a higher concentration of H⁺ on one side of the membrane. This creates a membrane potential. So when H⁺ moves down it's concentration gradient, the membrane potential decreases.



This makes C the correct answer.

There's a great diagram at this website:

https://chromoscience.com/2019/12/21/cotransport-coupled-transport-by-a-membrane-protein/