Rhizobium bacteria live in swellings on soybean roots. The bacteria change nitrogen gas into a form the soybean can absorb, and the soybean supplies the bacteria with sugars and a place to live. What type of relationship is this?

A sea lamprey attaches to a lake trout with a sucking mouth, rasps a hole in the skin and feeds on the trout's blood and body fluids for weeks. The trout grows slowly and often dies. How is this relationship best classified?

Barnacles cement themselves to the skin of a gray whale and filter plankton from the water rushing past as the whale swims. Whales carrying barnacles swim, feed and grow no differently from whales without them. Which term names this relationship?

A grouper holds still at a reef station while a cleaner wrasse swims over its body and into its mouth, eating the parasites and dead tissue it finds there. The wrasse gets most of its daily food this way. This relationship is an example of what?

Mistletoe growing on an oak branch pushes root-like structures into the branch and draws out water and dissolved minerals. The branch above the mistletoe produces fewer leaves each year and eventually dies back. What type of relationship is this?

A bromeliad grows perched on a high branch of a rainforest tree, catching rainwater in its leaves and taking minerals from dust in the air. It never taps the branch, and the tree's growth rate is the same with or without it. Name this relationship.

Ants live inside the hollow thorns of a bullhorn acacia and feed on protein bodies and nectar the tree produces. The ants swarm and bite any animal that starts to eat the leaves, and cut away vines that touch the tree. What is this relationship?

Varroa mites attach to honeybees and to bee larvae in the comb, feeding on their body tissue and passing viruses to them. Colonies with heavy mite loads raise fewer bees and often collapse over winter. How is this relationship classified?

A wood duck raises its brood inside a tree cavity that a pileated woodpecker chiseled out the year before and abandoned. The duck gains a sheltered nest site, and the woodpecker's nesting and feeding are unchanged. What is this relationship?

Single-celled algae live inside the tissue of coral polyps. The algae pass most of the sugars they make by photosynthesis to the polyp, and the polyp supplies them with shelter and with the nitrogen waste it produces. Name this relationship.

A brown-headed cowbird lays an egg in a warbler's nest and flies off. The warblers incubate it and feed the large cowbird chick, which takes most of the food brought to the nest, and fewer of their own chicks survive. What is this relationship?

Burdock seed heads are covered in stiff hooks that catch on a coyote's fur as it brushes past. The seeds are carried for kilometers and fall off far from the parent plant. The coyote feeds and moves the same as always. Which term names this?

A pistol shrimp digs and repairs a burrow in the sand that it shares with a goby. The nearly blind shrimp keeps one antenna on the goby, which watches for predators and flicks its tail as a warning so both can dive in. What type of relationship?

A golden jackal trails a hunting tiger at a distance and feeds on the meat left on a carcass after the tiger has eaten and moved away. The tiger kills and eats the same amount whether or not the jackal is following. Classify this relationship.

Pine roots and mycorrhizal fungi form a mutualistic relationship. Which statement describes what each organism gets?

Head lice living on a person's scalp are parasites. Which statement describes the effect on each organism?

The remora and the shark it rides on have a commensal relationship. Which statement describes what each organism gets?

Termites and the protists living in their gut are mutualists. Which statement describes what each organism gets?

A fish leech attaches to a trout's fin and takes repeated blood meals while the trout swims and feeds. The trout loses blood at the attachment site. This is a parasitic relationship.

In the relationship between honeybees and the flowering plants they visit, only the honeybee benefits.

The yucca plant and the yucca moth are mutualists. Which statement describes what each organism gets?

Dodder is a vine with no chlorophyll. It coils around a clover plant and pushes structures into the clover's stem. This is a parasitic relationship. Which statement describes what each plant gets?

In a field trial, aphid colonies tended by ants lost 8 percent of their aphids to predators, while untended colonies lost 45 percent. Ants with aphids nearby collected three times more sugar than ants without. What relationship do these results describe?

Puppies carrying intestinal roundworms gained 0.6 kg over four weeks, while worm-free littermates gained 1.8 kg. The worms grew and released eggs inside the intestine the whole time. What relationship do these data show?

Beetles carrying pseudoscorpions flew the same distances and lived as long as beetles without them. Pseudoscorpions that rode a beetle reached new fallen trees 200 m away, while those that walked traveled about 4 m. What relationship is this?

In night trials, bobtail squid carrying their glowing bacteria were caught by predators in 12 percent of trials, and squid without the bacteria in 61 percent. The bacteria grew to far higher numbers in the squid than in seawater. Name this relationship.

Moose calves carrying heavy winter tick loads lost large patches of hair, and 42 percent of them died before spring. Lightly infested calves had 6 percent mortality. The ticks fed on blood and produced eggs. What do these data show?

Sea cucumbers with emperor shrimp riding on them fed at the same rate and gained the same mass as sea cucumbers with no shrimp. The shrimp collected four times more food particles while riding than when moving on their own. Name this relationship.

A fig wasp crawls inside a fig, carrying pollen from the fig she hatched in, and pollinates the flowers there before laying her eggs. Her larvae develop inside some of those flowers. What is this relationship?

A clownfish shelters among the stinging tentacles of a sea anemone, which its mucus coating protects it from. The clownfish chases off butterflyfish that bite the anemone's tentacles. Which term names this relationship?

Bacteria living in the human large intestine feed on material the person cannot digest, and some of them make vitamin K, which the person absorbs and uses in blood clotting. How is this relationship classified?

Spanish moss hangs from the branches of a live oak and takes its water and minerals from rain and dust in the air. Oaks with and without it grow at the same rate. Why is this commensalism rather than parasitism?

A burrowing owl raises its young in a burrow that a prairie dog colony dug and later abandoned. The prairie dogs are not measurably affected. Why is this commensalism rather than mutualism?

Fleas live in a dog's coat, bite through the skin and feed on the dog's blood. The dog scratches constantly and can develop irritated, infected skin. Which term names this relationship?

Plasmodium is a single-celled organism that a mosquito bite delivers into a person's blood. It multiplies inside red blood cells and bursts them, and the person develops the fever and anemia of malaria. What relationship is this?

The fungus that causes athlete's foot grows in the dead outer layer of skin between a person's toes, digesting keratin there. The skin cracks, itches and can become infected by bacteria. How is this relationship classified?

A great horned owl seizes a rabbit, kills it and eats it within a few minutes. Why is this interaction classified as predation rather than parasitism?

Two species of frog in the same pond both feed on a limited supply of insects. When they live together, both species grow more slowly and produce fewer eggs than when either lives in the pond alone. Which term describes this interaction?

A tick stays attached to a deer and feeds on its blood for several days, then drops off. Why does a parasite like this tick usually not kill its host quickly?

On a rocky shore, two barnacle species settle on the same rock surface. Where they meet, one species grows over the other and crowds it off the lower rocks. Why is this competition rather than parasitism?