Compare and contrast the operation of negative and positive feedback mechanisms in maintaining homeostasis. Provide two examples of variables controlled by negative feedback mechanisms and one example of a process regulated by a positive feedback mechanism.

Calcium levels in Mr. Gallariani's blood are dropping to dangerously low levels. The hormone PTH is released and soon blood calcium levels begin to rise. Shortly after, PTH release slows. Is this an example of a positive or negative feedback mechanism? What is the initial stimulus? What is the result?

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Living organisms react to changes in their environment known as stimuli.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Homeostasis is the condition of having a dynamic equilibrium of the internal environment.