Biological Systems MCAT Practice Exam

What is passive immunity?

1. Self-generated antibodies by the immune system

2. Received antibodies from another individual

3. Development of memory cells upon infection

4. Immune response triggered by vaccination

The correct answer is: Received antibodies from another individual

Passive immunity refers to the acquisition of antibodies produced by another individual's immune system, rather than the individual's own immune system generating those antibodies. This form of immunity can occur naturally, as seen when a mother transfers antibodies to her fetus through the placenta or through breast milk after birth. Alternatively, passive immunity can also be acquired artificially, such as through the administration of immunoglobulin therapy, where pre-formed antibodies are given to an individual to provide immediate protection against specific pathogens. The other options highlight different aspects of the immune system but do not accurately describe passive immunity. For instance, self-generated antibodies signify active immunity, where an individual's own immune response produces antibodies following exposure to an antigen. The development of memory cells upon infection is also indicative of active immunity, which allows for a quicker and more robust response in case of future exposure to the same pathogen. Additionally, triggering an immune response through vaccination involves the body’s active response, creating memory cells and producing antibodies, which is fundamentally different from passive immunity.