Biological Systems MCAT Practice Exam 2025 – The Comprehensive All-in-One Guide for Exam Success!

The sympathetic nervous system plays a vital role in preparing the body for "fight or flight" responses during stressful situations. This system is activated in times of stress and triggers several physiological changes that enhance the body's ability to respond to threats.

Increasing heart rate and respiratory rate is a key characteristic of the sympathetic nervous system activation. By elevating heart rate, the system ensures that more oxygen-rich blood is pumped to muscles and vital organs, thereby preparing the body for rapid movement and heightened alertness. Simultaneously, an increase in respiratory rate allows for greater oxygen intake, ensuring that the body is well-oxygenated to sustain energy needs during potentially high-stress scenarios.

The other options, while they describe different aspects of human physiology, do not accurately reflect the role of the sympathetic nervous system during stress. For example, a "rest and digest" response is associated with the parasympathetic nervous system, which promotes relaxation and energy conservation rather than the heightened activity seen in stressful situations. Similarly, the sympathetic nervous system does not promote energy conservation; rather, it activates metabolic processes to provide the necessary energy for action. Lastly, the system actually increases blood flow to muscles to prepare for physical exertion, contrasting with the claim that it would reduce blood flow