Biology STAAR Practice Test 2026 - Free State of Texas Assessments of Academic Readiness Practice Questions and Study Guide

Red blood cells are responsible for carrying oxygen throughout the body. They contain a protein called hemoglobin, which binds to oxygen molecules in the lungs and transports them to tissues and organs that require oxygen for various metabolic processes. The structure of red blood cells, which are biconcave discs, increases their surface area for efficient gas exchange, making them highly effective for this function.

In contrast, platelets play a crucial role in blood clotting, helping to prevent bleeding; white blood cells are primarily involved in the immune response, defending the body against infections; while plasma cells are more specialized cells that produce antibodies and are involved in the immune response as well. Thus, red blood cells are uniquely adapted for the oxygen transport function within the circulatory system.