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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 the movements of hydrogen ions (H+), potassium ions (K+), sucrose molecules, and calcium ions (Ca2+) through a cell membrane. The relative concentrations of each ion (high or low) are provided. From left to right, the proteins are labeled A, B, C and D. What type of membrane protein is protein A?  

The 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. True or false? Upon binding insulin, an insulin receptor can directly phosphorylate a molecule of IRS. 

A cell responds to two types of signaling molecules. Estrogen is a signaling molecule that binds to an intracellular receptor known as an estrogen receptor (ER), ultimately causing gene expression. Insulin-like growth factor 1 (IGF-1) is a signaling molecule that binds to a membrane receptor (IGF-1R). Upon binding to IGF-1R, a molecule of IGF-1 activates a signaling pathway that can phosphorylate ER, enhancing the rate of gene expression caused by estrogen alone. The top figure shows the integration of the two signaling pathways. The bottom figure shows the rates of gene expression in a cell under four conditions, labeled 1 through 4.   In which condition was the cell most likely to be exposed to neither estrogen nor IGF-1?

The figure shows the permeability of a phospholipid bilayer for five molecules, named molecule A through molecule E. All of these molecules are the same size. Which molecule is likely the most hydrophilic? 

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?  

Gramática I. Oraciones. Complete each sentence with the correct forms of the verbs in parentheses. ¡OJO! Be sure to include the correct indirect object pronoun with each verb. (6×2=12) 1. Al señor López______ _________ (importar) comer sano. 2. A ti y a mí ___ ____ ____ _____ (apetecer) una sopa de pollo. 3. A usted _______ _________ (encantar) los tamales de queso con chile. 4. ¿A ti _______ ____________ (parecer) importante comprar frutas y verduras de productores locales? 5. A Eduardo y a Ana _______ _________ (gustar) la pizza napolitana. 6. A mí no _______ _________ (apetecer) los huevos rancheros.

Escuchar. Picadillo. César is describing one of his favorite dishes. Listen to what he says about it and then complete the sentences based on what you hear. (6×2=12) á é í ó ú ñ   1. El ingrediente principal del picadillo es la _____ de res picada. 2. Otros ingredientes incluyen ______  , ajo, pimientos, tomates y un poco de vinagre. 3. La abuela de César no le añade (add) ________ al picadillo porque a su familia no le gusta el sabor dulce. 4. Según la receta clásica, se sirve el picadillo con plátanos y ________. 5. Si quieres cocinar la versión “a caballo”, hay que sustituir el arroz por ________y añadir (add) _______ fritos. 6. A César le __________ el picadillo clásico de su abuela.

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 number of minutes in one hour is a variable.