**Text:**When human tissue, such as skin or a blood vessel, is torn or cut, the cells in the damaged region secrete a signal that activates specialized blood cells called platelets in the vicinity. As the platelets come in contact with one another, they begin to form a clot and release additional chemical signals to attract more platelets as well as other clotting factors until the bleeding is stopped.Which of the following correctly **describes** the feedback mechanism illustrated by the activation of the platelets?**Options:**A. It is an example of positive feedback because the initial activation of the platelets causes the activation of additional platelets.B. It is an example of negative feedback because the initial activation of the platelets is caused by a harmful stimulus.C. It is an example of positive feedback because the ultimate result of initial platelet activation causes the bleeding to stop.D. It is an example of negative feedback because the initial activation of the platelets causes the additional activation of different clotting factors.

Platelets is the constituent of blood cells other than red blood cells and white blood cells. These help in blood clotting.C. It is an example of positive feedback because the ultimate result of initial platelets activation causes the bleeding to stop. Explanation- The above example is of positive feedback because the initial signal causes the release of platelets that cause the release of additional platelets and clotting factors, the result of both these factors were to form the clot and stop the bleeding. Blood platelets and various clotting factors help in the formation of a cascade of reactions which ultimatly cause the blood clot. ADP, TxA2 functions as a positive-feedback mediator during platelet activation. Explanation for wrong answers- First option is incorrect as it is an example of positive feedback but this activates both platelets and clotting factors. Second option is incorrect as it is not an example of negative feedback because at the end the number of platelets and clotting factors are increased. Last options in correct as it is not an example of negative feedback.