Login

Join for Free!
119229 members


Diffusion and concentration gradient

Debate and discussion of any biological questions not pertaining to a particular topic.

Moderator: BioTeam

Diffusion and concentration gradient

Postby Aymeric » Sun Dec 15, 2013 1:02 am

Hello,

We have been working on the respiratory system and once more this involved concentration gradients.
I more or less understand how it works by now (it's been mentioned a lot in other systems as well) but what intrigues me is that the concentration gradient can be different for several types of molecules in the SAME environment. I don't get that...

For example, in the alveoli, dioxygen molecules get into the capillaries because O2 concentration is lower there. However, CO2 concentration is very high in the capillaries. So how do the O2 molecules "know" that this high concentration within the capillaries is from CO2 and NOT O2? Conversely, how do the CO2 molecules realise that the air in the alveoli is O2-rich but low in CO2...

At first I thought that diffusion depended on 'space', whereby any molecule tries to get as much space around itself as possible and hence moves towards lower concentrations. But the fact that CO2 is present in high concentrations where O2 wants to go is very counterintuitive, because both are molecules that take up space and intuitively should "repel" one another... And instead of that each type of molecule simply 'ignores' the presence of other types.

Thanks in advance for your insights.
Aymeric
Garter
Garter
 
Posts: 11
Joined: Fri Dec 13, 2013 10:29 am

Postby Arlen1991 » Sun Dec 15, 2013 7:10 am

I think this is the result of neural regulation. Transport and the distribution of related molecules is completed under the control of the brain via some specific receptor proteins .
Arlen1991
Garter
Garter
 
Posts: 2
Joined: Sun Dec 15, 2013 6:50 am

Postby Aymeric » Tue Dec 17, 2013 2:02 pm

Thanks for your reply, but there is no mention of any such mechanism at alveoli level, the exchanges there seem to be completely passive. Would you have any references about 'non-passive' exchanges in the alveoli? I have never heard of that and my course never mentions it.

Thanks!
Aymeric
Garter
Garter
 
Posts: 11
Joined: Fri Dec 13, 2013 10:29 am


Re: Diffusion and concentration gradient

Postby wildfunguy » Thu Dec 19, 2013 12:51 am

I don't see the problem.
It's all about net movement in each direction. If there is more O2 in region A than in region B, there will be more movement of O2 from A to B than from B to A. After all, O2 can't diffuse out of region B if it isn't already present in region B. If B is filled with mostly CO2, then most of the diffusion out of B will be of CO2.
wildfunguy
Coral
Coral
 
Posts: 109
Joined: Sat Feb 18, 2012 4:28 am

Postby Darby » Fri Dec 20, 2013 3:14 pm

Think about a crowd, with women and men, randomly moving across a sidewalk from one side of a park to the other. If the movement is random, men will gradually diffuse along their gradient, women along theirs, and even though they are all "people," the process still works...
Darby
Viper
Viper
 
Posts: 1265
Joined: Thu Mar 02, 2006 5:29 pm
Location: New York, USA

Postby Aymeric » Fri Dec 20, 2013 8:14 pm

Thank you two for your explanations! I guess my mistake was to think that elements move towards wherever they will have more space, whereas in reality they just move randomly and that's it. Right?
Aymeric
Garter
Garter
 
Posts: 11
Joined: Fri Dec 13, 2013 10:29 am

Postby Darby » Wed Dec 25, 2013 2:27 pm

At the atomic level, there is LOTS of space...they're just following the odds, really - if the concentrations are 5% and 70%, for every 5 particles headed one way, there's 70 headed the other.
Darby
Viper
Viper
 
Posts: 1265
Joined: Thu Mar 02, 2006 5:29 pm
Location: New York, USA

Re: Diffusion and concentration gradient

Postby JackBean » Thu Dec 26, 2013 5:49 pm

1) the answer of Arlen1991 is completely irrelevant to your question!
2) Darby's analogy is perfect
3) it's simply about entropy. The molecules move randomly in any direction without any knowledge of presence of other molecules (alike or different). So just by following probability they spread randomly after some time.
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
User avatar
JackBean
Inland Taipan
Inland Taipan
 
Posts: 5692
Joined: Mon Sep 14, 2009 7:12 pm


Return to General Discussion

Who is online

Users browsing this forum: No registered users and 7 guests