At night a great horned owl drops onto a deer mouse in a meadow, kills it, and eats it. The owl gains a meal and the mouse is killed. Name this interaction between the two organisms.

In a Serengeti grassland, a pride of lions and a clan of spotted hyenas both try to feed on the same zebra carcass, and each group gets less meat because the other is there. Name this interaction.

A honeybee drinks nectar from an apple blossom, then carries pollen on its body to the next blossom so that apples can form. The bee gets food and the tree gets pollinated. Name this interaction.

A tapeworm lives inside a dog's intestine and absorbs digested food, so the dog takes in fewer nutrients and loses weight. The worm benefits and the dog is harmed. Name this interaction.

Barnacles fasten to the skin of a humpback whale and filter food from the water as the whale swims. The barnacles get food and a place to live, and the whale is neither helped nor harmed. Name this interaction.

A wolf pack in Yellowstone chases an elk through deep snow, brings it down, and feeds on it. What term names the relationship between the wolves and the elk?

Hollow thorns on a bullhorn acacia shelter stinging ants, and the tree also grows tiny food packets the ants eat. The ants attack insects and vines that would damage the tree. Name this interaction.

Two sunflower seedlings sprout a few centimeters apart in one pot. Their leaves shade each other and their roots pull water from the same small volume of soil, so both grow more slowly. Name this interaction.

Mistletoe grows on an oak branch and pushes root-like structures into the branch to draw out water and minerals. The mistletoe gains and the oak branch weakens. Name this interaction.

A remora fish attaches to a shark with a suction pad on its head and eats scraps left over when the shark feeds. The remora gains food and the shark is neither helped nor harmed. Name this interaction.

A ladybird beetle walks along a rose stem and eats one aphid after another. The beetle gets food and the aphids are killed. What term names this relationship?

Threads of fungi wrap around pine tree roots. The fungi pass water and minerals from the soil into the roots, and the pine passes sugars it made back to the fungi. Name this interaction.

Fleas live in a house cat's fur and feed on the cat's blood. The cat scratches, loses a little blood, and gets skin sores, while the fleas feed and lay eggs. Name this interaction.

In a Texas pasture, white-tailed deer and cattle both graze the same grasses. In a dry summer the grass runs short and each group finds less food because the other is feeding there. Name this interaction.

A Carolina chickadee raises its young inside a tree hole a woodpecker made and later abandoned. The chickadee gains a safe nest, and the tree is neither helped nor harmed. Name this interaction.

A pod of orcas surrounds a harbor seal, catches it, and shares the meal. Which term names the relationship between the orcas and the seal?

A clownfish shelters among a sea anemone's stinging tentacles, which keep predators away. The clownfish chases off fish that nibble the anemone and stirs fresh water around it. Name this interaction.

A tick attaches to a white-tailed deer, feeds on its blood for days, and leaves the deer with a sore, irritated patch of skin. This relationship is parasitism.

In a mutualism, only one of the two organisms benefits from the relationship.

Cattle egrets walk beside grazing cattle and snap up the grasshoppers the cattle stir up from the grass. The birds get food and the cattle are unaffected, so this relationship is commensalism.

A great blue heron stands still in shallow water, stabs a small fish, and swallows it. The heron gains a meal and the fish is killed. Name this interaction.

A dodder vine winds around a clover plant and pushes structures into its stem to draw out sugars and water. The vine grows and the clover weakens. Name this interaction.

An orchid grows high on the bark of a rainforest tree, where it catches more light and rain. It takes nothing from the tree, and the tree is neither helped nor harmed. Name this interaction.

Bacteria live in a cow's stomach and break down tough grass the cow cannot digest alone. The bacteria get food and shelter, and the cow gets nutrients it could not otherwise reach. Name this interaction.

Two woodpecker species in one wood both need holes in dead trees to nest in, and dead trees are scarce. Each species raises fewer young where the other is present. Name this interaction.

A cleaner wrasse swims into a grouper's open mouth and eats the parasites attached there. The wrasse is fed and the grouper is rid of pests. Name this interaction.

Ants stroke aphids on a rose stem so the aphids release a sugary liquid the ants drink, and the ants drive off beetles that would eat the aphids. Which organism benefits in this relationship?

A burdock plant's hooked seed burrs catch in the fur of a passing deer and are carried far from the parent plant. The deer is not affected. Which organism benefits, and which is unaffected?

A roundworm lives in a pig's intestine, absorbs food the pig has digested, and the pig grows more slowly. Which organism gains and which loses?

A lichen on a rock is made of a fungus and an alga living together. The alga makes food from sunlight and the fungus holds water and grips the rock. Which organism benefits?

A cheetah chases down a young gazelle on an open plain and eats it. Which description of the outcome is correct?

Coyotes and red foxes in one valley both hunt the same rabbits, and rabbits are scarce this year. Which description of the outcome fits?

Moss grows on the shaded north side of a maple trunk, taking nothing from the tree and doing it no damage. Which description matches this relationship?

A sea otter dives, pulls a sea urchin off the rocks, and cracks it open to eat. Which pair of outcomes is correct?

A leech attaches to a swimmer's leg and feeds on blood for several minutes before dropping off. The swimmer is left with a small sore but is not killed. Is this predation or parasitism, and why?

A student calls the relationship between a mosquito and a deer predation. What makes parasitism the better name for it?

Two students disagree about a bird that nests in a cactus. One says mutualism, the other commensalism. What must they find out to settle it?

A relationship is described as mutualism, but a closer look shows one partner gains while the other is completely unaffected. Which name now fits, and why?

A hawk eats a rabbit, and a flea feeds on that same hawk's blood for weeks. What separates the two relationships?

Two plants growing in one patch of soil both take water from it, and each grows more slowly than it would alone. A student calls this parasitism. What is the correct name, and why?