Final answer:
The invasion protein in nitrogen-fixing symbionts is critical for facilitating the successful infection of host plant roots leading to nodule formation and nitrogen fixation, which is essential for converting atmospheric nitrogen to a usable form for plants, improving crop yields and agricultural production. Option b is correct.
Step-by-step explanation:
In the context of nitrogen-fixing symbionts, the invasion protein is responsible for facilitating the entry of symbiotic bacteria into plant root cells, which leads to the formation of nodules where nitrogen fixation takes place. Nitrogenase, the enzyme that fixes nitrogen, is inactivated by oxygen; therefore, nodules provide an oxygen-free environment essential for the process.
Nitrogen fixation is critical as it converts atmospheric nitrogen into ammonia, a form that plants can use. Using this natural process, plants gain access to an endless supply of nitrogen, enhancing agricultural production as nitrogen is necessary for the formation of nucleotides and proteins, thus improving crop yields and helping plants to compete with weeds.