Question

For each of the following feedback mechanisms, indicate whether it is an example if a negative or a positive feedback loop. Explain your reasoning.

a. A snowball rolling down a hill becomes larger and larger, making it roll faster and become larger still.
b. Iron is absorbed from digested foodstuffs through receptor-mediated pinocytosis in the small intestine. When iron concentrations in the blood rise above the set point, excess iron accumulates in the cells of the small intestine. This excess iron itself functions to suppress the futher active absorption.
c. Determined to earn an A in Human Physiology, you decide to seek help from a tutor. The tutor is helpful, but very expensive. In order to pay the tutor, you must start working nights, Working reduces your study time, and your grades fall in the course. Thus, you spend more time with the tutor, meaning you have to earn more money. As a result if working more, you decide to spend even more time with the tutor.
d. A decrease in set-point concentration for thyroid hormones results in a greater inhibitory signal from the thyroid gland (effector).
e. During the stage of a nerve impulse, sodium channels in the cell membrane are opened These opened channels allow sodium ions to diffuse into the cell, which in turn creates a slight change in voltage across the cell membrane. In response to this change in voltage, more sodium channels in the cell membrane are opened. This allows more sodium to diffuse into the cell and causes and even greater change in voltage across the membrane.

Answer 1

A . This is a positive feedback mechanism in which it is observed that the snowball increases in size with the bearing, thus the movement reinforces the size of the ball.

B .This is a negative feedback mechanism in which over time it is evident that iron levels in the body drop.

C . This is a negative feedback mechanism in which if more work is done at night the score will be decreased

D .This is also a negative feedback mechanism because when thyroid hormone levels drop, the hormone continues to decrease on its own.

E .This is a positive feedback mechanism in which sodium is observed as it passes through the cell membrane, making the process more active and causing more sodium to enter the cell.