2. Root nodules in alfalfa plants contain nitrogen fixing bacteria. These bacteria provide nitrogen to the plant and gain nutrition in return.

1. Hermit crabs use the shells of dead gastropods for shelter and protections. This helps the hermit crab, but does not affect the gastropods since they are already dead.

13. The South China Tiger kills and eats a blesbuck. This predatory act allows the tiger to receive nutrients and energy.

5. The Brown Headed Cowbird leaves its egg in the nest of an Eastern Phoebe. This helps the Cowbird reproduce successfully, but it causes the Phoebe to waste time and resources on another bird’s egg.

3. These ants receive housing and nutrition from the Bullhorn Acacia tree. In return the ants provide the tree with protection from other organisms.

10. A tick bites a young child and feeds on his blood. This helps the tick gain vital nourishment, but it costs the child blood and opens him up to infection.