Answer: Commensalism is a type of symbiotic relationship in which one organism benefits from the relationship, while the other organism is neither harmed nor benefited. Some examples of commensalism relationships are:
A. A blood tick attaching to a dog: This is not an example of commensalism, because the tick benefits from the relationship by feeding on the dog's blood, while the dog is harmed by the tick's feeding. This is more accurately described as a parasitic relationship.
B. Two spiders weaving webs at two different corners of a garden: This is not an example of commensalism, because there is no relationship between the two spiders. They are simply occupying different areas of the same habitat.
C. A bear finding a den that used to belong to another, now-deceased bear: This could potentially be an example of commensalism, depending on the circumstances. If the bear benefits from using the den without harming the previous inhabitant or the den itself, then it could be considered commensalism. However, if the bear causes damage to the den or takes over the den and prevents the previous inhabitant from using it, then it would not be considered commensalism.
D. An orchid growing on tree bark: This could potentially be an example of commensalism, depending on the circumstances. If the orchid benefits from growing on the tree bark without harming the tree, then it could be considered commensalism. However, if the orchid causes damage to the tree or takes resources from the tree, then it would not be considered commensalism.
Overall, commensalism relationships involve one organism benefiting from the relationship without causing harm or providing benefit to the other organism.