Can we use "the" (definite article) with nouns to refer to a group of that name?

For example, on learnenglish.britishcouncil.org and this article said:

to say something about all the things referred to by a noun:

  • The wolf is not really a dangerous animal (= Wolves are not really dangerous animals)
  • The kangaroo is found only in Australia (= Kangaroos are found only in Australia)
  • The heart pumps blood around the body. (= Hearts pump blood around bodies)

Is that really right?

Because I only saw in that site and I know that when "the" comes before adjectives it refers to a group of people.

  • It certainly is right but I cannot explain why. It means "the class of things in which an individual member is known as..." As the examples indicate, it seems to suggest a didactic function. I can't imagine ever saying such a sentence unless I were speaking at a lecture. – JeremyC Feb 24 '18 at 17:10
  • @Nigel J Yes, it was a good question. When first asked. – Edwin Ashworth Feb 24 '18 at 17:11