U4L2: Feedback Systems

Figure 1 is a proposed model of the feedback system controlling erythrocyte (red blood cell) production.

Air is less dense at very high elevations, so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1, if a person travels from sea level to a high elevation location, which of the following correctly predicts the response to the decreased blood oxygen level?

• More erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes.

• More erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.

• Less erythropoietin will be secreted from the kidneys, decreasing production of erythrocytes.

• Less erythropoietin will be secreted from the kidneys, increasing production of erythrocytes.

True or false: Positive feedback mechanisms in biological systems serve to stabilize conditions by returning the system to a target set point.

• True

• False

Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following statements about the activity of platelets best explains a positive feedback mechanism?

• Activated platelets release chemicals that inhibit blood clot formation

• Activated platelets release signaling molecules that inhibit cell division in damaged tissue

• Activated platelets constrict the blood vessels, stopping blood flow

• Activated platelets release chemicals that activate more platelets