Question

1. Indicate which of the following best illustrates the concept of positive feedback? The concept of negative feedback? Make sure to justify your answer.

1. An increase in the concentration of H+ in blood causes an increase in H+ excretion in the urine.

2. An increase in the carbon dioxide concentration of the blood stimulates breathing, which increases the rate at which carbon dioxide is eliminated from the body.

3. Contractions of the uterus push the fetus against the cervix, which triggers release of oxytocin into the bloodstream. Oxytocin then stimulates stronger contractions of the uterus.

Answer 1

Negative feedback mechanism: It responds to the change detected and produces an effect opposite to the change detected.The system reacts in such a way to arrest the change or reverse the direction of change.

The first two given conditions are examples of negative feedback mechanism.

An increase in H+ concentration in the blood causes the excretion of H+ through urine and hence lowering the H+ concentration in the blood.

An increase in Carbondioxide concentration in the blood stimulates breathing ,which increases the rate at which Carbondioxide is eliminated from the body.

In both the cases an effect opposite to the change detected is produced.

Positive feedback mechanism:It responds to the change detected and produces an effect in the direction of the change detected i.e, it enhances the change.The system reacts in such a way as to increase the intensity of the change in the same direction.

Ex: Contraction if the uterus pushes the fetus againts the cervix,which triggers release of oxytocin into the blood stream.Oxytocin then stimulates stronger contractions of the uterus.