The schematic graph below represents the nullclines (solid curves) and a few selected trajectories (dotted curves) for a system composed of two proteins (X and Y) with a complex regulatory behavior. According to the graph, indicate whether each of the following statements is (Y) or is not (N) acceptable. Your answer would be a four-letter string composed of letters Y and N only, e.g. YYYY.

( ) The system is bistable.
( ) There are three steady states in the system.
( ) The system contains positive feedback.
( ) The system contains delayed negative feedback.

Question

The schematic graph below represents the nullclines (solid curves) and a few selected trajectories (dotted curves) for a system composed of two proteins (X and Y) with a complex regulatory behavior. According to the graph, indicate whether each of the following statements is (Y) or is not (N) acceptable. Your answer would be a four-letter string composed of letters Y and N only, e.g. YYYY.
  
( )	The system is bistable.
( )	There are three steady states in the system.
( )	The system contains positive feedback.
( )	The system contains delayed negative feedback.

Quizplus · Accepted Answer

The spiral trajectories represent oscillations (resulting from delayed negative feedback) as the system approaches one of the two stable nodes. The steady state in the middle is unstable.

The Schematic Graph Below Represents the Nullclines (Solid Curves) and a Few