An оrgаnism must regulаte the cоncentrаtiоn of solutes in its body fluids, called osmolarity. An extreme change in osmolarity will alter the diffusion of water through cell membranes, potentially disrupting the functions of cells. In a healthy human, a homeostatic system ensures that the osmolarity of blood stays within a certain range. When the osmolarity increases, nerve cells in the hypothalamus detect the diffusion of water through channel proteins in their membranes (osmosis). These channels activate a signaling pathway that causes a nerve cell to secrete a hormone called vasopressin. A molecule of vasopressin can bind to receptors in the membranes of kidney cells, causing the kidneys to excrete less water as urine. Over time, the osmolarity of blood returns back to its expected range. The figure shows a path model of the homeostatic system that regulates the osmolarity of blood. This regulated variable is represented by a dashed box. Other variables are represented by a solid black box. An arrow connecting one box to another indicates a relationship between two variables. The value above each arrow indicates the slope of the linear relationship between the variables connected by the arrow. In the model above, which units describe the slope of the linear relationship between the osmolarity of blood and the activity of channel proteins in the hypothalamus?
The tоp figure shоws а pаth mоdel of the homeostаtic system that regulates the osmolarity of blood. This regulated variable is represented by a dashed box. Other variables are represented by solid black boxes. An arrow connecting one box to another indicates a relationship between two variables. The sign above an arrow (+ or -) indicates whether the variables are related positively or negatively. The bottom figure is a set of plots. Which plot above shows the relationship between the osmolarity of blood (independent variable) and the activity of channel proteins (dependent variable)?