grammar - Is there any difference in meaning between the definite, the indefinite, and the zero article when we make generic nouns?

I learned in class that:

a. A tiger is a dangerous animal.

b. Tigers are dangerous animals.

c. The tiger is a dangerous animal.

These three sentences are used generically.

But I just saw:

1. The tiger is in danger of becoming extinct.



2. Tigers are in danger of becoming extinct.


3. A tiger is in danger of becoming extinct.

the previous sentences and number '1' and '2' are used generically but example 3. is not.

Is there anyone who can tell me why the latter examples are different from the former ones? Also, is there any difference in meaning depending on the article?