phloem vs sieve tube

phloem and sieve tube both are nouns.

Word	Noun	Adjective	Verb	Adverb
phloem	Yes	No	No	No
sieve tube	Yes	No	No	No

phloem (noun)	sieve tube (noun)
(botany) tissue that conducts synthesized food substances (e.g., from leaves) to parts where needed; consists primarily of sieve tubes	tube formed by cells joined end-to-end through which nutrients flow in flowering plants and brown algae