Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

What role do red blood cells play in the circulatory system?

1. To digest food

2. To transport oxygen to tissues

3. To produce hormones

4. To protect against pathogens

The correct answer is: To transport oxygen to tissues

Red blood cells, or erythrocytes, play a crucial role in the circulatory system primarily by transporting oxygen from the lungs to various tissues throughout the body. This is made possible by the presence of hemoglobin, a protein contained within red blood cells that binds to oxygen molecules. When blood circulates through the lungs, red blood cells pick up oxygen during respiration. As these cells travel through the body's capillaries, they release the oxygen to the surrounding tissues, which is essential for cellular respiration and energy production in cells. Moreover, red blood cells also contribute to the transport of carbon dioxide, a waste product of metabolism, back to the lungs for exhalation. This dual role in gas exchange underscores their importance in maintaining the body's homeostasis and overall metabolic function. In contrast, other options reflect functions that are typically associated with different types of cells in the body: digestion is primarily the function of the digestive system, hormones are produced by the endocrine system, and protection against pathogens is mainly the role of white blood cells and the immune system.