What would happen if an organism does not have a functional immune system?

An organism lacking a functional immune system would experience a significant vulnerability to infections. The immune system is responsible for identifying and combating pathogens such as bacteria, viruses, fungi, and parasites. Without an effective immune response, the organism would struggle to defend itself against these harmful invaders. This would lead to an increased likelihood of infections, which can be severe and potentially life-threatening.

In contrast, the other options suggest outcomes that are not aligned with the role of the immune system. Thriving in any environment, being resilient to diseases, or having enhanced recovery from illness would imply a level of health and resistance that the absence of a functioning immune system would compromise. Thus, the inability to mount an immune response makes the organism highly susceptible to various infections and diseases.