The difference between "component" and "constituent"

[Tinagik]

Hello. I have yet another question for Mister Macawber, or for anyone who has the time to help. This is from a CPE Reading Exam. Here is part of the text + the question:

Caves

Research establishments and university departments around the world have invested years of research time in all aspects of caves, mainly their origins, their hydrology and their biology. Caves constitute a small but rather mysterious 1)... of the natural environment--as such they arouse our curiosity and challenge our desire for knowledge...

The options are:
A)constituent B)compartment C)complement and D)component

The correct answer is:
D) component

Below are some definitions of the words (found in the online Webster's Dictionary).

component (noun) = an abstract part of something, a constituent part or feature of a whole
constituent (noun) = a component part/ an abstract part of something

The word "component" sounds correct to me. It's a word I would use here, but that is not a suitable explanation to give to my students. Would you please tell me why "component" is the correct choice and "constituent" is not? Is "component" the correct answer because of the word "rather" used in the sentence?

Also, which word would be correct if the sentence were written in this way?:

"Caves are a constituent of the natural environment"
"Caves are a component of the natural environment"

It seems that "constituent" is correct and "component" is incorrect. Is this because "constituent" stands alone in this sentence and "component" doesn't. The word "component" would maybe require an adjective beforehand?

Again, I am confusing myself. Time to go to bed:)

Thank you for your help! Tina

[Kanjikook]

Good question! To me, constituent suggests a discrete item, whereas component could have the sense of being made up of smaller parts (a component of a car (the engine) could itself have constituent parts (pistons, block etc.)). In the sentence given, I'd say "[All the different types of] Caves [all together] constitute...a component" .

The sentence also says "Caves constitute...", so to have "constitute a...constituent" sounds a bit odd (again, assuming that a constituent is not made up of smaller part), which is why component is better.

Does that help?

Suggestions from others?

[Tinagik]

To Kanjikook

Thank you for responding, and so quickly too! Your explanation makes a lot of sense to me. You really helped! Thanks a lot!

Tina:)