2
$\begingroup$

The difference between facilitated diffusion and active transport is that facilitated distribution occurs down a concentration gradient and active transport occurs against a concentration gradient. I understand that, as a result of these differences, active transport uses ATP so that it can bind to the carrier protein, however I don't know what is meant by going against a concentration gradient or down a concentration gradient.

In short, I would like to know the difference between going against and down a concentration gradient. A definition of what a concentration gradient is might clarify things a little further as well, since the definition I have doesn't help much.

Improve this question
$\endgroup$

2 Answers 2

Reset to default
7
$\begingroup$

"Concentration" is "how much stuff is there someplace?" "Concentration gradient" is "how much is concentration changing from point A to point B?"

Imagine a terrain where concentration is represented by height.

"Down" a concentration gradient means from high concentration to low concentration - this is the direction things would move via simple diffusion.

"Up" or "against" a concentration gradient means from low concentration to high concentration. Moving in this direction requires some sort of energy input, such as active transport using ATP, or an electrical gradient, or something else.

Improve this answer
$\endgroup$
-1
$\begingroup$

Moving against a concentration gradient means that the substance is moving from a low concentration to a high concentration. Moving down (descending) a concentration gradient means that the substance is moving from high concentration area to a low concentration area.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Welcome to Biology.SE! Your answer doesn't seem to be adding anything to the already existing answer. In addition, answers are much more likely to receive a favorable response if they include supporting references (primary literature is best). ——— Please take the tour and then consult the help pages for additional advice on How to Answer effectively on this site and then edit your answer accordingly. Thanks! 😊 $\endgroup$
    – tyersome
    Oct 26, 2019 at 16:59

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .