Bacteria living in cows' stomachs that help them break down the cellulose in grass, and also provides nourishment for the bacteria

A bee feeds on the pollen of a flower, and the pollen is spread from flower to flower by the bee flying off to other flowers

A remora fish attaches itself to the underside of a shark without harming the shark, and eats leftover bits of food from the sharks meals

Lichen is made up of a fungus and algae on a tree trunk. Algae create carbohydrates via photosynthesis, the fungus utilizes the carbohydrates and the fungus provides water and nutrients for the algae.

A butterfly - weed provides food for a butterfly and is pollinated by the butterfly at the same time

A lizard living in an abandoned rat hole in the desert. The rat moved on to a new home and is unharmed, and the lizard benefits from shelter

Tree frogs utilize plants as protection, and the plants are unharmed

Fleas bite the cats skin to suck their blood, which causes the cat to itch and possibly get sick

A mosquito biting a human, and the human develops a red itchy bump