Wow, that a really interesting question. If one species dies out and becomes extinct it could literally change the world. Take for instance bees. Bees are one of the most important species we have and yet they are in serious danger of becoming extinct because of the chemicals used in agriculture. Bees are our main pollinators, they are responsible for over 90% of the fruit, vegetables, nuts, and seeds that we eat on a daily basis. You want to talk about important species, bees are top of the list.
If we lose bees, we lose all the plants that bees pollinate. Then we loose all the animals that rely on those plants, and that takes us all the way up the food chain! That's including humans.
Hope this helps.
