EOC Biology STAAR prep
Four common relationships between organisms are listed in the box. Which statements best describe these relationships?

A. Relationships 1 and 4 are examples of mutualism. Relationship 2 is an example of commensalism. Relationship 3 is an example of parasitism.
B. Relationships 1, 2, and 4 are examples of mutualism. Relationship 3 is an example of parasitism.
C. Relationship 1 is an example of commensalism. Relationships 2 and 4 are examples of mutualism. Relationship 3 is an example of predation.
D. Relationships 1 and 2 are examples of commensalism. Relationships 3 and 4 are examples of mutualism.
Please explain, I don't want just an answer.

The correct answer is option B

Species interactions are categorized based on their reciprocal effects (the effects that the interaction has on each species/individual involved).

1. Bees pollinate plants as they move from flower to flower collecting pollen.

This is a mutualistic relationship because the both species involved in this interaction benefit from the interaction. The bee benefits because it obtains nectar which is provided by the plant. The plant benefits because the bee carries the plants pollen to other plants, allowing the plant to reproduce.

2. Green algae grow on the backs of spider crabs living in shallow water.

This is another example of a mutualistic relationship because both species involved in this interaction benefit from the interaction. The spider crab benefits from the camouflage that the algal growth provides, while the algae benefits from the protection from predators provided by the spider crab.

3. Fleas living on skin of dogs and obtaining nutrients from dogs blood.

This is a parasitic relationship because one of the species benefits from the interaction while the other species in negatively impacted by the interaction. The flea benefits from the nutrients obtained from the dogs blood while the dog is negatively impacted by the fleas presence (loss of blood, discomfort).

4. Nitrogen-fixing bacteria obtain nutrients from host plants and use the nitrogen to supply host plants with nitrogen.

This is an example of mutualism because both species in this interaction are benefitting from the interaction. The nitrogen fixing bacteria benefit by receiving nutrients from the host plant while the host plant is benefitting from receiving nitrogen from the bacteria.

Feel free to comment and ask any additional questions.