A Level Biology Practice Exam

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Which of the following best describes platelets?

  1. Red blood cells with a nucleus

  2. Colorless disc-shaped cell fragments

  3. White blood cells

  4. Large nucleated cells

The correct answer is: Colorless disc-shaped cell fragments

Platelets are best described as colorless disc-shaped cell fragments. They play a crucial role in the process of hemostasis, which is the stopping of bleeding in the body. Platelets are derived from larger precursor cells called megakaryocytes found in the bone marrow. When these megakaryocytes break apart, they release small fragments into the bloodstream, which are the platelets. These fragments lack a nucleus, distinguishing them from red and white blood cells. Their primary function is to aggregate at sites of injury, activating the clotting cascade to form blood clots, which prevent excessive blood loss. Understanding the structure and role of platelets is essential for comprehending their significance in cardiovascular health and wound healing.

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