Final answer:
The rhizosphere is the soil layer directly influenced by plant roots, enriched by root secretions, and inhabited by beneficial microorganisms such as rhizobia which assist in nutrient absorption. The correct option is B.
Step-by-step explanation:
The rhizosphere refers to the soil layer directly influenced by plant roots. This zone is characterized by the activity of root secretions and the presence of microorganisms that interact with the root system. Considered a dynamic and complex environment, the rhizosphere is crucial for nutrient cycling, as root secretions can influence the microbial population and, in turn, these microbes can aid the plant in obtaining nutrients.
An example of such interaction is with rhizobia, soil bacteria that enter a symbiotic relationship with leguminous plants, helping in nitrogen fixation within the rhizosphere. Moreover, the structure of roots, including root hairs, plays a significant role in increasing the surface area for absorption, thus actively affecting the interactions within the rhizosphere.
Root hairs are delicate structures that extend from the root epidermis, which increases the volume of soil the roots can influence for efficient water and nutrient uptake. Hence, B is the correct option.