Essential Knowledge 2.C.1

Organisms use feedback mechanisms to maintain their internal environments and respond to external environmental changes.

Negative feedback mechanisms maintain dynamic homeostasis for a particular condition (variable) by regulating physiological processes, returning the changing condition back to its target set point.

Examples

• Operons in gene regulation
• Temperature regulation in animals
• Plant responses to water limitations)

Positive feedback mechanisms amplify responses and processes in biological organisms. The variable initiating the response is moved farther away from the initial set-point. Amplification occurs when the stimulus is further activated which, in turn, initiates an additional response that produces system change.

Examples:

• Lactation in mammals
• Onset of labor in childbirth
• Ripening of fruit

Alteration in the mechanisms of feedback often results in deleterious consequences.

Examples:

• Diabetes mellitus in response to decreased insulin
• Dehydration in response to decreased antidiuretic hormone (ADH)
• Grave's disease (hyperthyroidism)
• Blood clotting

Students should be able to:

LO 2.15 Justify a claim made about the effect(s) on a biological system at the molecular, physiological or organismal level when given a scenario in which one or more components within a negative regulatory system is altered.

LO 2.16 Connect how organisms use negative feedback to maintain their internal environments.

LO 2.17 Evaluate data that show the effect(s) of changes in concentrations of key molecules on negative feedback mechanisms.

LO 2.18 Make predictions about how organisms use negative feedback mechanisms to maintain their internal environments.

LO 2.19 Make predictions about how positive feedback mechanisms amplify activities and processes in organisms based on scientific theories and models.

LO 2.20 Justify that that positive feedback mechanisms amplify responses in organisms.