A An initial increase in cell-wall loosening at the root tip activates auxin transporter relocalization that increases local auxin and loosening; the response causes cell-wall loosening at the root tip to decrease back toward its starting level.
B An initial increase in cell-wall loosening at the root tip activates auxin transporter relocalization that increases local auxin and loosening; the response causes cell-wall loosening at the root tip to increase further.
C An initial increase in cell-wall loosening at the root tip and auxin transporter relocalization that increases local auxin and loosening are both shown, but the response changes only an unrelated output.
D The response is shown as turning off before it can affect cell-wall loosening at the root tip, so the original variable does not move farther from its start.
