Plants use a homeostatic system to regulate the osmolarity of the fluid in xylem. As the osmolarity of this fluid increases, the cells of the roots produce proteins that transport solutes through the cell membrane. These proteins actively transport solutes from the roots into the soil, decreasing the osmolarity of the cells. As the osmolarity of root cells decreases, water moves from these cells into the xylem via osmosis, decreasing the osmolarity of the fluid in the xylem. The top figure shows a set of linear relationships among three variables involved in regulating the osmolarity of fluid in the xylem. The bottom figure shows four path models, labeled A through D, that represent possible homeostatic systems that regulate the osmolarity of fluid in the xylem. The 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 sign above an arrow (+ or -) indicates whether the variables are positively or negatively related.  Which path model accurately describes the relationships among the three variables?

The figure shows a homeostatic system with four components labeled A, B, C, and “regulated variable.” Which component of a homeostatic system measures the value of a regulated variable?

Type 2 diabetes is a disease that rarely occurs in people under 40 years of age. However, some people have been known to develop this disease at an earlier age.  The set below contains the ages at which type 2 diabetes was diagnosed in 54 people. Each value is the age, in years, of a person who was diagnosed with the disease.   Age (years) =  [8, 9, 9, 9, 9, 9, 10, 10, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 16, 16, 17, 17, 17, 17, 17, 18, 18] What percentage of ages are less than 10 years?

The figure shows four frequency distributions, labeled A through D.  Which plot contains the frequency distribution that corresponds to a normal probability distribution with the smallest standard deviation?  

An organism must regulate the concentration 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.  Alcohol inhibits the release of vasopressin by nerve cells. Typically, a person who has not consumed alcohol has a concentration of vasopressin between 0.5 pg ml-1 and 2 pg ml-1, but a person who has ingested alcohol has a much lower concentration of vasopressin.  The figure shows a path model of the homeostatic system that regulates the osmolarity of blood. This model also describes the effect of alcohol on the concentration of vasopressin in blood. The 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.  Which concentration of alcohol in the blood would cause the osmolarity of the blood to increase by 11 mmol L-1?

The figure shows four containers of the same size. The purple dots represent molecules within each container.  The temperature in each container is identical. In which container would you expect to observe the most number of interactions between molecules?   

An organism must regulate the concentration 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. If the rate at which the kidneys excrete water decreases by 3.45 mL min-1, how would the osmolarity of blood change? The osmolarity would _______.

True or false? The value of π (pi) is a variable.

An enzyme called phosphofructokinase binds a substrate called fructose-6-phosphate (F6P) and catalyzes a reaction to form a product. The activity of this enzyme depends on the presence of a molecule called adenosine triphosphate, or ATP.  The figure shows the relationship between the concentration of F6P and the activity of enzymes, in either the presence or absence of ATP. The activity of enzymes was measured as the rate at which products were formed (also called the rate of reaction). ATP likely binds to ________ of the enzyme.

Thyroxine (T4) is a hormone that certain animals use to regulate the activity of cells. The production of T4 depends on the concentrations of two other hormones: thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH).  TRH comes from a part of the brain called the hypothalamus. This hormone can bind to receptors in another part of the brain, called the pituitary gland. Upon binding to a receptor, TRH activates a signaling pathway that causes a cell to release TSH.  The figure shows the signaling pathway that controls the production of T4. TSH binds to receptors in the thyroid gland, causing cells of this gland to produce T4. The production of T4 depends on an enzyme called thyroid peroxidase (TPO), which creates T4 by adding an iodide ion (I-) to a molecule.  A nonpolar structure enables T4 to diffuse through the phospholipid bilayer of any cell, including cells of the hypothalamus and the pituitary gland, where T4 inhibits the release of TRH and TSH, respectively. Choose the word or phrase that accurately completes the following sentence. When TSH binds to a receptor, the concentration of cAMP in a cell should ______.