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what exactly is a gradient?

It is been with me for some time this question. I cant understand what a gradient is. When it says there's a water potential gradient what is it. All I ever know is x moves from a point of higher concentration to a point of lower concentration.

Thanks amigos

Reply 1

Revenged

If something is said to move "down a concentration gradient" then moves from a higher concentration to a point of lower concentration - so its diffusion...

If something is said to move "against the concentration gradient" then it moves from a lower concentration to a point of higher concenetration - so its active transport...

It is the same for water potential... but i think water can only move "down a water potential gradient" - so its osmosis... I don't think water can move against the conc gradient...

Reply 2

acvaos

But whats a gradient itself?

Reply 3

Revenged

From wiki...

http://en.wikipedia.org/wiki/Slope

"Given two points (x1, y1) and (x2, y2), the change in x from one to the other is x2 - x1, while the change in y is y2 - y1. Substituting both quantities into the above equation obtains the following:"

gradient = y2 - y1 / x2 - x1

or

gradient = change in y / change in x

Reply 4

Abra

Difference in y / difference in x.

Reply 5

Abra

i drew this, if it helps..

Reply 6

acvaos

Thank you guys but im looking for a more biological definition rather a mathematical one.

Reply 7

Tom H

Anything where one variable increases or decreases in response to another?

Example: Concentration decreasing with distance from source

However as the molecule diffuses so it is equally concentrated everywhere, then the definition is not satisfied as the concentration is no longer changing with distance from source, and you've lost your gradient.

Gradients are important as thanks to thermodynamics molecules always tend to move from a high concentration at source, to a lower one in the surrounding areas (thus providing those surrounding areas with molecule). If the molecule was allowed to become equiconcentrated around all of those areas there would be no gradient. And therefore no method of providing areas with molecule.

Also, the bigger a gradient (ie LOTS of molecule in one area in comparrison to another accesible area) leads to a faster rate of diffusion, which can also be very important biologically if you're in need of lots of molecule fast.