Bistability in a Biological System Can Be Accompanied by Hysteresis

Multiple Choice

Bistability in a biological system can be accompanied by hysteresis. Consider switchlike cellular responses to a signal molecule, as shown in the following graphs. In each graph, the solid curve corresponds to the change in cellular response when the signal concentration is being increased over time, whereas the dashed curve corresponds to the change when the signal concentration is being decreased. Which graph do you think corresponds to a system with a greater degree of hysteresis? What mechanism is responsible for this behavior?

A) Graph A; negative feedback
B) Graph A; positive feedback
C) Graph B; negative feedback
D) Graph B; positive feedback