1 Answers

Which of the following has the most primitive respiratory system?

Posted by: 3447 views

Which of the following has the most primitive respiratory system?

A. insect

B. fish

C. snail

D. mouse




This question is really difficult to properly respond to, Primitivity can easily be determined if all the organisms listed in the options evolved directly or indirectly from one another.

For instance, fishes evolved differently when compared with snails, this is why they have ventilation gills while snails have diffusion gills as well as lungs in most species. Fishes are vertebrates, snails are not. The evolution of vertebrates like fish, and invertebrates like snail, are far apart.

So, if I must compare between fish and snail, which is more primitive? I think I would go with fish…

Going by the theory of evolution which shows that all animals evolved out of water, fishes are totally aquatic animals which perform respiration through the gills. Whereas snails, which have both gills and lungs, are among the first invertebrates to move into land just like the amphibians.

Fishes do not have lungs, snails do; the common notion that snails breath through their skin is simply not true for land snails. Snails breath in air directly through a nose-like opening called pneumostome, this air gets processed in the lungs to absorb oxygen and release carbondioxide.

Although water snails could breath through their skin, most fishes too breath through their skin.

Presently, it is a common notion that gills are more primitive than lungs. Gills absorb oxygen from oxygen-rich water, but lungs absorb oxygen directly from air.

Now for the right answer to the above question:

  1. Option A is incorrect; assuming all animals evolved from water, then the insects are more advanced than the snails.
  2. Option B is correct; fishes have only gills and no lungs.
  3. C is incorrect; snails have both gills and lungs.
  4. D is not the correct answer; mouse is clearly the most advanced among the options.


You may please note that:

  • Another complication arises with insects; they have no gills, no lungs, they only have tracheae. Now the big question is… did these tracheae evolve from snail gills?
  • Fishes’ respiration are taken as more primitive than snails’ because fishes breath through gills only, but snails breath through both gills and lungs.

You are free to add your own answers below this page to assist others improve their learning.

You can also click the golden ASK A QUESTION BOTTON down this page to raise new related questions… OUR COMMUNITY OF EXPERTS WILL BE MORE THAN HAPPY TO TACKLE IT…

/ culled from 2015 JAMB-UTME biology past question 1 /

1 Answers

  1. +1 Votes Thumb up 0 Votes Thumb down 0 Votes

    Ur very correct chief 🙌

    Anzy - Mar 22, 2022 | Reply

Answer Question