[chris (OP)]

I received this question as an email from Dale Reynolds today. I thought I'd share the question and answer in case anyone else is wondering the same thing.

"Hello Chris and the Team,

I am not sure if you will ever get bored of hearing you are a brilliant show, but my girlfriend, Rachael, and I are (still) avidly working our way back through all the podcast archives (only 60 hours to go for her, I have a much better 20 remaining!)

We noticed you have talked about IMAX on several occasions, and having one near to us in Birmingham we visited. Having spent 45 minutes under water with 3D Sharks swimming around us, we were left with a conundrum of questions which can only be answered in one way; put them to the naked scientists.

I reckon that this a question for Helen, as a marine Biologist, but Rachael think s your sponge like absorbing brain will answer it in a flash.

So -
part A) do fish / sharks have lungs working on the same principal as our own i.e. external respiration (air goes in / O2 absorbed into the blood / CO2 passed from the blood into the lungs). We can not see how this can occur as we cant see how air (atmospheric or otherwise) can enter the lungs.

part 2) how is O2 removed from the surrounding water and converted into a usable substance. We know it is something to do with the Gills, but, in lay-mans terms, how do these gills work?"

ANSWER SENT TO DALE:

The long and short is that sharks don't have lungs - they are fish so they have gills. Gills consist of dense networks of thin-walled blood vessels over which water is pumped. This allows carbon dioxide in the blood to move into the water, and oxygen from the water to move into the blood.
 
The gills are arranged into a "counter current" system so the water flows through in the opposite direction to the blood. This means that oxygen will always be picked up via the blood, and carbon dioxide will always be picked up by the water.
 
The oxygen gets into the water in the first place in several ways. The most important sources are marine plants, which photosynthesise and produce oxygen as a by-product, and also oxygen from the air dissolving in the water.
 
The carbon dioxide entering the water, on the other hand, makes perfect plant food - the marine plants and plankton absorb it and, again using photosynthesis, turn it into sugars and oxygen.
 
 
Chris

[Karen W.]

Thanks Chris... I knew thet did not have lungs, but did not know the details of their gills and how they worked. There is another question here somewhere from Loretta about Lungs in a fish.. This post of yours would be beneficial there also!

[moonfire]

Excuse moi!  It was only referenced as a joke about cpr moderator queenie..hehe...I know they don't have lungsie...I have a child who wants to be a marine biologist...don't ever tell him I joked about his little friendsies...LOL  How to give CPR to a fish is what I referenced my question as...you assumed I meant for lungs...LOL  ;-)

[Karen W.]

Yes indeedy I did ! LOL You are the best!!LOL LOL  Secrets safe with me!! LOL

[moonfire]

LOL  you are too funny....i love ya anyways gal! ;-)

[Karen W.]

 Hey being a goof ball doesn't mean you get to stop being my pal! LOve ya too! LOL Thinking Daniel went to sleep! TIRED BOY!

I really need to blow up my Kitchen which thread do I go to to to get information on making a small bomb for that!LOL When its all over, I'll just sweep it out the door! I DON"T WANT TO CLEAN.....WAHHHH!! Oh well nobody else will and I have been on strike for over a week and it has done no good! Its worse now and they still won't help behind themselves.. I want a one way ticket out of here soon.. LOL I think I will go get me a hot tub room tomorrow night and just stay in the tub all night! My hot tub motor quit and they want 1000 dollars to replace said motor I can buy a whole new hotub for 2000 dollars so why on earth would i pay for them to give me a new motor my tub is 15 or so years old!! No way! New hot tub.. I think I will just go rent the room for the night! MAybe I will stay long enough to make like a fish and develope gills!

[moonfire]

Uh, oh...not a good sign...if you turn blue at the gills who is going to do fish cpr on ya?  ;-)  Who said they were going to stop being your pal???  LOL

[Karen W.]

So you luvs me anyways.. Ok me too! LOL Yeah haven't got my gilman here to resessitate me  if I drown.. But I did spend 2 hours in hot tub! and then went out and met bob and we ate a very nice italian meal had a nice talk and I think my kids will live for another day!!! I did not develop gills, but did find that I have some really bouyant body parts! I havent been in that much water in several years... It was nice I was in heaven.. stormin like crazy and pouring down rain on my head but I did not care it was quite nice!

[moonfire]

I wonder how long a fish can live outside of water? 

I have some really bouyant body parts too Karen..hehe 

Mmmm, jealous...love the rain!

[Karen W.]

It was very nice to sit and soak like that! I don't know but I wonder too!

[moonfire]

Hmmm, thinking about gills for a moment....I wonder if anyone here has disected a fish...I have a cow's eye and a frog...but not a fish...

[neilep]

What about Lungfish ? http://en.wikipedia.org/wiki/Dipnoi  he asks..not bothering to read the very article he's just posted a link to !

[Karen W.]

I found That article interesting but hard to read as Most of the references were things I couldn't pronounce and had to look up to understand what they were! They do breathe air, but how where are the lung like units?

[ChaoticBliss]

So actually I just learned this today in AP Biology, and so here is my answer to this. The fish opens its mouth and takes in a mouthful of water. It closes its mouth and the gills flare, and the stream of water passes over the gills. Tiny frills in the gills filter oxygen, and the tiny capillaries that are so close to the skin here are able to absorb the oxygen. Look mom, no lungs!

~ChaoticBliss

[iko]

Hi friends,

allow me...a little help from a picture!

http://futurescientists.tamu.edu/lesson11/graphics/fishgill.jpg

[paul.fr]

Hi friends,

allow me...a little help from a picture!

http://futurescientists.tamu.edu/lesson11/graphics/fishgill.jpg

Iko, none of that rhymes!  []

[iko]

Ops! uhm, sorry about that!

From the filament gill
O-two flows down the hill
and in one second or two
big fish is out of the blue!

Do NOT puke  []  please

ikod