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The figure shows two boxes containing chemical structures. The box on the top contains the structure of an amino acid called lysine. The box on the bottom contains the structure of four other amino acids, labeled A through D. In both boxes, the R group of each amino acid is highlighted. Which amino acid has an R group that can bond with the R group of lysine? 

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). Which statement could explain the effect of ATP on the activity of this enzyme?

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 _______.

Muscle cells require calcium ions (Ca2+) to contract. When the concentration of calcium in the intracellular fluid decreases, a muscle cell relaxes. When the concentration of calcium in the cytoplasm increases, a muscle cell contracts.  To prevent unwanted contraction, a muscle cell stores most of its Ca2+ in a specialized compartment within the cell, called an organelle. An organelle has its own membrane, similar in structure to the membrane that surrounds the cell. The concentration of Ca2+ in the intracellular fluid depends on the activity of transport proteins in the cell’s membrane and organelle’s membrane. The figures show a system of transport proteins that regulate the movement of Ca2+ in a cell. The top figure illustrates the function of the transport proteins in this system. The lower left-hand portion of the bottom figure shows a muscle cell as the concentration of calcium in the intracellular fluid decreases, leading to relaxation. The lower right-hand portion of the bottom figure shows a muscle cell as the concentration of calcium in the intracellular fluid increases, leading to contraction. Which phrase accurately completes the following sentence? If the number of Na+/Ca2+ antiporters in the cell membrane increases, the concentration of ________ inside the cell would increase.

The top figure shows a signaling pathway for a signaling molecule called insulin, which binds to an insulin receptor. In the figure, phosphorylation of a protein by a kinase is represented by a “P” in a yellow circle.  The bottom figure shows three relationships (labeled A through C) between the time after a cell was exposed to insulin and the concentration of phosphorylated AKT in that cell. The fourth relationship, labeled “typical negative feedback,” illustrates the change in the concentration of phosphorylated AKT in a typical cell.     Imagine a cell that has been exposed to a drug that inhibits the activity of S6K proteins. Which relationships illustrate a potential pattern of change in this cell? 

The top figure shows a signaling pathway for a signaling molecule called insulin, which binds to an insulin receptor. In the figure, phosphorylation of a protein by a kinase is represented by a “P” in a yellow circle. The bottom figure shows four relationships (labeled A through D) between the time after a cell was exposed to insulin and the concentration of phosphorylated AKT in that cell.  Which relationship illustrates the negative feedback that occurs in the signaling pathway activated by insulin?

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 ______.

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.  Doctors recorded the ages at which type 2 diabetes was diagnosed in 54 young people. The data are represented in the frequency distribution below. The top figure shows a frequency distribution of the data and the bottom figure shows four probability distributions, labeled A through D. Which plot represents the normal probability distribution that best fits the data?

The figure shows four scatter plots, labeled A through D.  show the same data, but each plot shows a different linear model of these data (red line). The axes are scaled the same for all plots.  Which plot shows the best linear model of the data?

An organism must regulate the concentration of solutes in its body fluids, also referred to as 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 a person becomes dehydrated, their osmolarity increases. When the osmolarity increases, nerve cells in the hypothalamus detect the diffusion of water, also known as osmosis, through channel proteins in their membranes. These channels activate a signaling pathway that causes a nerve cell to communicate with other nerve cells located in the “thirst center” of the hypothalamus. The activity of these nerve cells affect a person’s behavior, causing them to seek out and ingest water. The top figure shows a path model of the homeostatic system that regulates the osmolarity of blood. This regulated variable is represented in the bottom figure 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 positively or negatively related.  Which component in this model is most likely a sensor?