OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What do platelets do when a blood vessel is damaged?

Increase white blood cell production
Transport nutrients
Initiate clotting at the injury site
Release antibodies

The correct answer is: Initiate clotting at the injury site

Platelets play a crucial role in the body's response to damaged blood vessels. When a blood vessel is injured, platelets immediately adhere to the exposed area and begin to aggregate, forming a temporary plug. This process is known as hemostasis, and it serves to prevent excessive bleeding. The platelets release various chemical signals that attract more platelets to the site, and they activate additional clotting factors in the blood, which work together to reinforce the platelet plug and eventually form a stable blood clot. This mechanism is essential for preventing blood loss and facilitating healing at the injury site. Other options do not relate directly to the immediate function of platelets in response to vascular damage. For instance, while increased production of white blood cells is part of the immune response, it does not directly relate to clotting. Transporting nutrients is primarily a function of red blood cells and plasma, not platelets. The release of antibodies pertains to the immune response against pathogens, which is separate from the clotting process.