AP Biology Unit 4 MCE

The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system?

After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels.

Trypsinogen is split by the enzyme enterokinase to form an activated molecules of the protease trypsin. Which of the following would confirm that the activation of trypsin in an example of how a positive feedback mechanism can amplify a biological process?

The trypsin produced by the reaction is capable of splitting and activating additional trypsinogen molecules.

The p53 protein regulates a cellular response to DNA damage. Based on the diagram above, which of the following best describes the role p53 in the response to DNA damage?

phosphorylated p53 stimulates transcription of p21, and the resulting p21 protein suppresses cell division until the DNA damage is repaired