Blog

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 figure shows the chemical structure of an amino acid. The R group is highlighted with a blue box. True or false? The R group of this amino acid is hydrophobic.

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? 

The figure shows a phospholipid. Regions X and Y have unique structures and functions. The table contains four potential combinations of chemical properties to describe Region X and Region Y. Potential Combinations Combination Region X Region Y    A hydrophobic, charged, polar hydrophobic, charged, nonpolar    B hydrophobic, charged, polar hydrophillic, uncharged, nonpolar    C hydrophilic, charged, polar hydrophobic, uncharged, nonpolar    D hydrophilic, uncharged, nonpolar hydrophobic, charged, polar Which combination of chemical properties applies to Region X and Region Y?  

A biologist wanted to know the number of insects that occur in a square meter of land. They counted insects on 20 plots, each having an area of 1 m2. The following set of numbers represents the number of insects on these plots:  Number of insects = [150, 150, 162, 168, 171, 171, 182, 184, 188, 199, 199, 199, 220, 220, 228, 228, 232, 244, 253, 253] Use this sample to answer the following question.   What is the relative frequency of the value 199?

The figure shows four frequency distributions, labeled A through D.  Which plot contains the frequency distribution that is best described by a normal probability distribution with a mean of 80?

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 probability distribution of body mass, as measured in kilograms (kg).    Which value is more than one standard deviation greater than the mean body mass? 

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.  Complete the following sentence. If a person has ingested alcohol, the osmolarity of the blood would ______.

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?

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?