A Level Biology Practice Exam

What defines natural active immunity?

1. It results from vaccinations against pathogens

2. It occurs when the body produces antibodies in response to an infection

3. It is permanently developed and cannot be lost

4. It is an immediate response without memory cells involved

The correct answer is: It occurs when the body produces antibodies in response to an infection

Natural active immunity is characterized by the body's ability to produce its own antibodies in response to an infection. This happens when a pathogen enters the body, triggering the immune system to recognize the foreign invader and mount a defense, which includes the production of specific antibodies to combat the infection. This process also typically leads to the generation of memory cells that will help the body respond more effectively if the same pathogen is encountered in the future. Other options, such as those related to vaccinations, pertain to artificially acquired immunity rather than natural immunity. The notion of permanent development is not entirely accurate, as immunity can wane over time. Additionally, an immediate response without memory cells does not reflect the typical function of natural active immunity, which involves a delayed response as the immune system learns and remembers the pathogen for future defenses.