Final answer:
The conjunction 'but' in the sentence 'Lichen spreads on the tree but does not kill it.' connects two main clauses within a compound sentence, neither directly connecting subjects, predicates, nor objects.
Step-by-step explanation:
In the sentence "Lichen spreads on the tree but does not kill it.", the conjunction "but" is used to connect two main clauses within a compound sentence. A compound sentence consists of two or more main clauses that are of equal importance to the overall meaning of the sentence. Each main clause contains both a subject and a predicate and can stand alone as a sentence if necessary. In this case, the conjunction "but" does not directly connect with subjects, predicates, or objects, but rather intwines the two clauses to express a contrast between the ideas they contain. The subject of the first clause is "lichen," and the predicate is "spreads on the tree," while the subject for the second clause remains "lichen," and the predicate is "does not kill it."