Biological Systems MCAT Practice Exam

What characteristic of capillaries aids in gas exchange?

1. Their thickness

2. They are lined with muscle

3. Walls are single cell thick

4. High pressure blood flow

The correct answer is: Walls are single cell thick

Capillaries are specialized blood vessels that play a crucial role in the exchange of gases, nutrients, and waste products between the blood and surrounding tissues. The characteristic that significantly aids in gas exchange is that the walls of capillaries are single cell thick. This thinness facilitates diffusion, allowing oxygen and carbon dioxide to move easily across the capillary walls. The single-cell thickness minimizes the distance that gases must travel, enhancing the efficiency of gas exchange. As blood flows through these narrow vessels, the proximity to tissue cells allows for rapid uptake of oxygen and release of carbon dioxide. This structural adaptation is vital for maintaining the body's homeostasis and ensuring that all cells receive adequate oxygen while removing carbon dioxide effectively. While factors such as the thickness of the vessel walls, the presence of muscle lining, and blood flow pressure do play roles in the circulation and distribution of blood, they do not specifically enhance the gas exchange process to the same extent as the thin walls of capillaries.