Why arthropod has not evolved to be huge?

[Tyto alba]

Q: Why arthropods have not evolved to be huge? 1. Homework Statement
Arthropods have not been able to achieve great size because
(1) the type of organ systems they possesses could not support·such a development
(2) they would be unable to successfully reproduce
(3) chitin is brittle and must be thick to bear the pull of muscles
(4) their vision is not good enough to hunt larger prey

2. The attempt at a solution

I went through berkeley.edu and figured out three points:

1.A large organism molting will have the huge risk of predation. It would need to hide rather frequently as the skeleton hardens.
2. The appendages which are mostly tubular chitinous structures won't support the shear increase in body volume which increase 8 folds with ever 2 fold increase in length.
3. The present respiratory system won't be efficient.

So,

(1) the type of organ systems they possesses could not support·such a development - Not all systems' a problem
(2) they would be unable to successfully reproduce -ruled out looks not an issue, early maturation, high number of offsprings
(3) chitin is brittle and must be thick to bear the pull of muscles-yeah, if the volume increases and the exoskeleton doesn't become thick enough it won't be able to support the muscles
(4) their vision is not good enough to hunt larger prey-looks not an issueSo answer 3 ?

 

[Bandersnatch]

3. The present respiratory system won't be efficient.

(1) the type of organ systems they possesses could not support·such a development - Not all systems' a problem

You just need one system to be not up to the task.

 

[epenguin]

Q: Why arthropods have not evolved to be huge?

I went through berkeley.edu and figured out three points:

1.A large organism molting will have the huge risk of predation. It would need to hide rather frequently as the skeleton hardens.
2. The appendages which are mostly tubular chitinous structures won't support the shear increase in body volume which increase 8 folds with ever 2 fold increase in length.
3. The present respiratory system won't be efficient.

maybe there is no "right answer" to this question. Yours appear to be me reasonable conjectures. How can you sharpen them to something more scientific? For 3 can you make a comparison with other organism types? Aquatic and terrestrial. Can you beef up 2 with some more known scaling laws for physiological functions?

 

[Tyto alba]

You just need one system to be not up to the task.

Though you have a point thinking about how the MCQs are solved I don't think one should go with this. Sometime when one is unsure one has to weigh the different options and having a plural form also knocks down one of them.

maybe there is no "right answer" to this question.

I think you are right.

How can you sharpen them to something more scientific? For 3 can you make a comparison with other organism types? Aquatic and terrestrial. Can you beef up 2 with some more known scaling laws for physiological functions?

To be honest I avoided doing that as it will take some good amount of time, going through the arthropods resp. sys and other related stuffs. I wanted to know that if my conjectures are right, I think they are now.
I'll return to this question once my impending Exams are over. Thank you :)

 

[Ygggdrasil]

FWIW, the answer that came to my mind first after reading the thread title and before seeing any of the options, would be that the respiratory system would not work.

 

[epenguin]

Maybe they were bigger in e.g. The cretaceous when everything was, different temperature and oxygen levels.