Tigers are in danger of becoming extinct. A tiger is in danger of becoming extinct. I'm sorry that for some reason i didn't see this question when it first got sent in, which apparently was nearly a month ago. This is a subject on which i have rather strong views, which i pass on to my students in introductory lectures. All tigers are in danger of extinction.
Some tigers are in danger of extinction.
This has nothing to do with grammar per se. There is a unicorn in the garden. In a hole in the ground there lived a hobbit. My toothbrush is pregnant. 3 is angry.