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Steroid hormones are insoluble in water; they are carried by transport proteins in the bloodstream of an organism.   Given that water is the most abundant molecule in blood, predict the chemical properties of the outer surface and interior of a transport protein that carries a steroid hormone.

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 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.  Which variable directly affects the activity of nerve cells in the “thirst center” of the hypothalamus?

Escribir. Una receta. Imagine that you attended a potluck party last weekend. Each person brought a dish to share, and yours was very popular! You’ve been asked to share how you made it. Write an email to your friend explaining how you made the dish. You need to write 5 sentences and your email should be in the past. (10 pts.)  á é í ó ú  Anoche….. para la fiesta de….. Primero….. Segundo…. Después…. Por último…. 

A company that makes athletic shoes wanted to design a running shoe for female marathon runners. To inform the design of this shoe, the company measured the body mass of 200 marathon runners. The plot shows the frequency distribution of body mass, as measured in kilograms (kg).  Which value is closest to the median of body mass?

Cortisol is a signaling molecule that regulates gene expression in the cells of a mammal.  Cortisol enters a cell and binds to a protein called a cortisol receptor. Binding of cortisol facilitates the phosphorylation of the cortisol receptor, which then can enter the nucleus and affect transcription.  The figure below shows a system of two genes whose transcription is regulated by cortisol. The IL10 gene codes for a protein called interleukin 10. The BGLAP gene codes for a protein called osteocalcin. A cortisol receptor can activate or repress the transcription of a gene by binding to a regulatory element. For example, a cortisol receptor activates transcription of the IL10 gene but represses transcription of the BGLAP gene.   When a person experiences stress, their adrenal gland releases cortisol, increasing the concentration of cortisol throughout the body. As a person sleeps, the concentration of cortisol in their blood decreases to nearly zero. After waking, the concentration of cortisol increases by four to seven times the concentration during sleep.   Complete the following sentence. During sleep, a cortisol receptor is _______ to be bound to the regulatory element of the IL10 gene.

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 protein is protein A?  

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. If the concentration of iodide ions (I-) in the thyroid gland decreases, the concentration of T4 in a cell of the thyroid gland 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 word or phrase accurately completes the following sentence? If the concentration of sodium ions (Na+) outside of a muscle cell increases, the rate at which calcium ions (Ca2+) are transported out of this cell would _______.

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

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. About 1 in 200 people have a genetic condition called Graves’ disease. A person with this condition produces an excess of proteins that bind to TSH receptors, activating more of these receptors than usual. The next figure shows four hypothetical relationships between the number of TSH receptors activated by proteins and the concentration of T4 in a cell, labeled A through D. Which relationship accurately describes the expected relationship in a patient with Graves’ disease?