root cap vs plant organ

root cap and plant organ both are nouns.

Word	Noun	Adjective	Verb	Adverb
root cap	Yes	No	No	No
plant organ	Yes	No	No	No

As nouns, plant organ is a hypernym of root cap; that is, plant organ is a word with a broader meaning than root cap:

root cap: thimble-shaped mass of cells covering and protecting the growing tip of a root
plant organ: a functional and structural unit of a plant or fungus

root cap (noun)	plant organ (noun)
thimble-shaped mass of cells covering and protecting the growing tip of a root	a functional and structural unit of a plant or fungus