"Chatte" is a female cat. "Chat" is a masculine cat. "Le" is used for masculine nouns, right? So "le chatte" is wrong because we're talking about a feminine cat but the article is for a masculine noun.
For me appears two choices that could be correct: "Le chat est un animal" and the "La chatte est un animal". But as in the english sentence I can't determine whats is the sex of the a animal shouldn't be "Le chat est un animal" the correct answer???
Does it matter. Learning a language is being able to communicate in that language. If you have been understood, that's enough for now. Refine the articles (female /male gender) and conjugations later. I feel this way anyway.