Ontario Grade 9 Science Class Practice Exam 2025 - Free Grade 9 Science Practice Questions and Study Guide

The selection of red blood cells, white blood cells, platelets, and plasma as the primary components of blood is accurate and reflects the essential elements that make up blood and its functions within the body.

Red blood cells, also known as erythrocytes, are crucial for transporting oxygen from the lungs to the tissues and facilitating the return of carbon dioxide from the tissues back to the lungs. This function is vital for cellular respiration and energy production.

White blood cells, or leukocytes, play an important role in the immune system. They help defend the body against infections and foreign invaders, making them essential for maintaining health and wellness.

Platelets, or thrombocytes, are involved in blood clotting, which is necessary to stop bleeding when injuries occur. They aggregate at the site of a wound and work to form a clot, preventing excessive blood loss.

Plasma is the liquid portion of blood, constituting about 55% of its volume. It carries hormones, nutrients, waste products, and proteins throughout the body, facilitating essential biological processes.

Together, these components work synergistically to ensure the body operates effectively, thus confirming the correctness of selecting this option.