生物科問題 {air sacs}

2014-03-10 6:43 am

我做到條關於breathing system既MC,唔明,想問下大家.

How can the steeper concentration gradient maintained in the lungs?
(1) Continuous blood supply to the lungs.
(2) Dense network of capillaries surrounding the air sac.
(3) The capillaries are very close to the alveoli.
(4) Oxygen combines with haemoglobin.
A. (1) and (2) only
B. (1) and (4) only
C. (1), (2) and (3) only
D. (1), (2) and (4) only

答案點解唔係D, 而係B?
Thanks!!!

更新1:

That means the dense network of capillaries just increase surface area for gaseous exchange. Right? If I think The dense network surrounding air sac or air sacs, the blood carries away the gas (oxygen) rapidly. Therefore, it can maintain the steeper concentration gradient. Is it correct??

回答 (1)

[匿名]

2014-03-11 12:10 am

✔ 最佳答案

There is network of capillaries surrounding air sacs, but if the network becomes
denser, there is less or even no effect on the concentration gradient ie. the
concentration gradient will not become steeper even if the network is denser. Also,(2) states that there is a capillary network surrounding a single air sac only.
However, the fact is that there is such kind of network surrounding all air sacs in
lungs. So the problem comes from the word ' dense ' and the singular word form of ' sacs '.

事實上, 這條問題根本是在咬文嚼字, 下次做問題要小心。

I assume you have already type every word of the question correctly.

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