A Level Biology Practice Exam

What defines a symbiotic relationship?

1. One organism feeds off another without benefit

2. Complete independence between organisms

3. Two organisms coexisting for mutual benefit

4. Competition between species for resources

The correct answer is: Two organisms coexisting for mutual benefit

A symbiotic relationship is characterized by the interaction between two different organisms that live together in close physical proximity, often to the benefit of both. In a mutualistic symbiotic relationship, both organisms derive benefits that contribute to their survival, growth, or reproduction. For example, in the mutualism between bees and flowering plants, bees obtain nectar for food while simultaneously helping plants with pollination, enhancing the plants' reproductive success. The other options describe different types of interactions that do not define a symbiotic relationship. One organism feeding off another without benefit indicates parasitism but does not reflect the nature of mutual cooperation found in a symbiotic relationship. Complete independence between organisms refers to a situation where they do not interact in any way, which is contrary to the essence of symbiosis. Finally, competition between species for resources points to an antagonistic interaction, where organisms vie for the same resources, again lacking the mutual benefit aspect inherent in symbiotic relationships.