focus vs take heed

focus is a noun but take heed is not a noun.

Word	Noun	Adjective	Verb	Adverb
focus	Yes	No	Yes	No
take heed	No	No	Yes	No

As verbs, take heed is a hyponym of focus; that is, take heed is a word with a more specific, narrower meaning than focus:

Other hyponyms of focus include absorb, engross, engulf, immerse, plunge, soak up, steep, recall, think, zoom in, hear, listen.

focus (noun)	take heed (noun)
maximum clarity or distinctness of an image rendered by an optical system
maximum clarity or distinctness of an idea
the concentration of attention or energy on something
a fixed reference point on the concave side of a conic section
a point of convergence of light (or other radiation) or a point from which it diverges
a central point or locus of an infection in an organism
special emphasis attached to something

focus (verb)	take heed (verb)
become focussed or come into focus	listen and pay attention
put (an image) into focus
direct one's attention on something
bring into focus or alignment; to converge or cause to converge; of ideas or emotions
cause to converge on or toward a central point