Bootcamp Bio test 5 Q 24

[PocketRocket]

24) In birds, which of the following extra-embryonic membranes allows gas exchange?
Answer: Chorion
However; the Allantois is also one of the options and that is what I though helped the embryo exchange gases and other waste. Why is Chorion the right answer?

I also came across this piece of information on wikipedia:

"During growth and development of the embryo, there is an increased need for oxygen. To compensate for this, the chorion and the allantois fuse together to form the chorioallantoic membrane. Together these form a double membrane, which functions to remove carbon dioxide and to replenish oxygen through the porous shell."

So in this case isn't it both the chorion and the allantois that are responsible for gas exchange?

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[FeralisExtremum]

So in this case isn't it both the chorion and the allantois that are responsible for gas exchange?

Technically no, although the extra-embryonic membranes are always a bit of a confusing area when they come up because of overlap in functions after they fuse. The chorion in birds is involved in gas exchange, the allantois is used to store waste in the form of uric acid. Sure, they later fuse together and the fused product helps with waste/gas exchange, but you should assume in the question that they are referring to the function of these membranes before such a fusion takes place (otherwise including both as an answer choice would make it impossible to answer).

Look at it this way - if you're asked a similar question about extraembryonic membranes in humans, you know that the chorion eventually fuses with maternal tissue to form the placenta, and the allantois ends up becoming the umbilical cord. But if you were asked about the function of these individual membranes you couldn't just say "well eventually they become the placenta and umbilical cord and do waste/gas/nutrient exchange so that's their function". These questions generally refer to the individual functions before fusion with other membranes/tissues.

 

[DAT Destroyer]

24) In birds, which of the following extra-embryonic membranes allows gas exchange?
Answer: Chorion
However; the Allantois is also one of the options and that is what I though helped the embryo exchange gases and other waste. Why is Chorion the right answer?

I also came across this piece of information on wikipedia:

"During growth and development of the embryo, there is an increased need for oxygen. To compensate for this, the chorion and the allantois fuse together to form the chorioallantoic membrane. Together these form a double membrane, which functions to remove carbon dioxide and to replenish oxygen through the porous shell."

So in this case isn't it both the chorion and the allantois that are responsible for gas exchange?

You are right Pocketrocket, Allantois does participate in the gas exchange, but only at the later stages of the embryo. In early stages Chorion's function is to facilitate the gas exchange because it lines the inside of the egg shell. The major function of the Allantois is to store metabolic waste material.

Hope this helps.

 

[PocketRocket]

Awesome, this makes sense. Thank you guys!