AP BIO CHAPTER 4 RETAKE

A person with diabetes mellitus is likely to have a deficiency or poor response to insulin. Elevation of blood glucose levels will typically lead to a concordant rise in insulin. However, in some of these patients, insulin is ineffective in its ability to regulate blood sugar levels. Which of the following is the unresponsive mechanism?

Negative Feedback

Observe the diagram below. Which of the following does this diagram represent?

This is a protein ligand since the molecule attaches to a receptor on the outside of the cell membrane.

Several sweet potatoes were cut into identical-sized cubes, weighed, and placed into open beakers with solutions of different sucrose (sugar) concentrations at 22 ∘ C. After 24 hours, the cubes were blot dried and weighed again. The percent mass change for each potato was determined and then graphed. Use the straight line on the graph to approximate the solute concentration (in M) of the sweet potato cells.

0.7

Many cells face serious difficulty living in a hypotonic environment and adapt in various ways to prevent cytolysis due to excessive water movement. Plant cell walls are one such adaptation to osmosis. By applying pressure in the form of turgor pressure on the inside of the wall, plants can prevent further movement into the plant and thus avoid cytolysis. A particular plant cell is placed in an open container of water containing a 0.75 M solution of sucrose at 20∘C. Calculate the turgor pressure required to allow the plant to be at equilibrium with the environment and prevent water entry into the plant cell.

18.26 bar

The sodium-potassium pump is essential to the repolarization of the neurons in our nervous system after an action potential. The pump works tirelessly to restore a − 70 mV gradient across our neurons in order to reset them to allow for more action potentials to occur. A diagram of the sodium-potassium pump at work is shown below. Based on the diagram, which of the following statements successfully describes the type of transport provided by the sodium-potassium pump?

Active Transport

A student filled three dialysis bags with different concentrations of a starch solution, and one bag was filled with distilled water. The bags were then placed in separate beakers of distilled water. Dialysis bags model the selective permeability of cell membranes and allow very small molecules, ions and water to pass through according to the surrounding concentration gradient. Starch is too large a molecule to pass through the dialysis membrane. The student massed the bags every five minutes to monitor the amount of mass gained or lost by each bag over the course of 30 minutes. The percent change in mass for each bag was calculated, and the data were plotted in the graph below: Which of the following lines on the graph would the student have obtained with the data from the bag with the most concentrated starch solution?

B

Eukaryotic cell membranes are considered to be fluid due to their ability to move and flow, and they are also considered to be mosaic because of the collection of glycolipids, glycoproteins, and cholesterols embedded within and throughout. Which of the following is NOT a way that components of the cell membrane maintain homeostasis?

Cytoskeletal filaments provide structural integrity and pathways for intracellular molecular movement.

Cells of the immune system rely on cell signaling in order to incite the immune response from all aspects of the body. These signals may increase the production of immune cells, aggregate macrophages, and divert the body's energy to fighting the pathogen. An example of this signaling is shown below. Which of the following cell signaling types BEST describes the interaction between the T-cell and the antigen-presenting cell?

Direct contact

When a pathogen enters the body, it is recognized by immune cells that then respond to the pathogen. Which of the following identifies the component of the pathogen's cell membrane most likely to be recognized by an immune cell?

Glycoproteins

Osmoregulation is essential to all organisms as it maintains homeostasis of the organism's water content. Osmoregulation in unicellular freshwater organisms like amoeba and paramecia involves an organelle called the contractile vacuole, which collects excess water as it accumulates in the cell and pumps it out. The graphs below plot contraction rate in contractile vacuoles vs. surrounding solution concentrations. Which of the following statements BEST explains the response when paramecia are placed in a beaker of distilled water to which a 5% NaCl solution is added dropwise?

Graph A illustrates the decrease in contraction rate that will occur as a result of negative feedback to the increase in surrounding solute concentration.

The fluid mosaic model of cell membranes describes the role of several components of the membrane. Which of the following BEST describes the role of cholesterol in the cell membrane?

It stabilizes the cell membrane.

A carrier protein transfers a solute across the phospholipid bilayer via facilitated diffusion and behaves much like an enzyme-substrate reaction. Which of the following is a distinction between the process by which an enzyme converts substrate to product and facilitated transport?

Solutes are able to undergo transport without chemical modification.

A student studying osmosis prepares the experiment in the image below. Before placing the potato cores in their respective beakers, the student massed both potato samples. After 40 minutes, the student removes the potato cores and weighs them again. The student knows that potato cells are permeable to water. Which of the following results will the student MOST likely observe in the potato core from the water-only beaker?

The final mass of the potato increased.

In a grocery store, vegetables are often sprayed with water. When sprayed, vegetables look crisper to the consumer. Which of the following statements BEST explains why this occurs?

The vegetable cells take in water using passive transport due to the higher concentration of solute inside of the vegetable cell.

Intravenous (IV) fluids are used to maintain fluid balance, replace fluid losses, and treat electrolyte imbalances. In an experiment involving IV fluids and hydration, a researcher placed one drop of human blood into each of three separate vials, and the illustrations below represent what was observed when the three blood samples were viewed under a microscope: Which of the following provides a scientific question that the researcher was attempting to answer?

What is the maximum and minimum IV solution concentration that red blood cells can tolerate?

The regulation of glycogen metabolism results in a cascade of reactions that produce forms of glucose. Based on the model of a signal transduction pathway, which of the following is the role of cAMP in the glycogen metabolism pathway?

cAMP in a signal transduction pathway is to function as a second messenger to activate a cascade of proteins that signal a response.

Hormones are chemical messengers that travel via the bloodstream and trigger cellular responses in a wide variety of target cells. The diagrams below illustrate the main difference in signaling pathways between steroid and protein hormones. This indicates that the cell signaling pathway of steroid hormones differs from the pathway of protein hormones in that steroids

pass freely through the cell membrane and travel into the nucleus, which results in enzyme activation and transcription. Protein hormones bind to membrane receptors and initiate a transduction pathway, which results in a series of enzyme activations, ending in a response in the nucleus.

A cross-country athlete has just come into the emergency room with severe dehydration. A doctor must decide what type of solution to pump into her veins so that she survives. The choices are pure water, 0.9% saline, and 1.8% saline. The doctor does not remember which solution is which, so she treats blood samples that she has placed on microscope slides with each solution and observes what occurs. Blood cells are approximately 0.9% saline. Which of the following solutions should be chosen to rehydrate the athlete?

0.9% saline

Pheromones are air-born chemicals that are sensed through olfaction. In deer, females release a sexually attractive pheromone during mating season that is sensed by male deer. Which of the following explains why only certain cells in the male deer receive pheromone signals, while the pheromones are exposed to all cells in the male deer?

Only certain cells in the male (particularly cells involved in the sex response) have receptors that bind to the female deer pheromone.

Refer to the diagram below. Which of the following identifies a potential cellular response in Step 3?

Binding of transcription factor dimer to DNA.

Gas exchange between the capillaries and the alveoli in the lungs is essential to the process of cellular respiration in the cell. The plasma membranes of both the alveoli and the capillary are important to ensuring that oxygen and carbon dioxide are transported in the appropriate direction. Which of the following statements successfully describes the direction in which oxygen and carbon dioxide move between the capillary and the lungs as well as the type of movement that this represents?

Oxygen enters the blood and carbon dioxide enters the lungs through simple diffusion.

Plants are very susceptible to changes in water content. Angiosperms have developed numerous mechanisms to help maintain water balance and homeostasis. One structure that plays an important part in this is guard cells. These unique cells respond to turgor pressure by opening and closing to release water, as seen below. Which of the following statements BEST describes the position of the guard cells if the plant is lacking water?

The guard cells will be flaccid and closed due to low turgor pressure.

Aquaporins are integral proteins of the plasma membrane whose role is to allow the passage of water molecules down its concentration gradient. Recent observations have shown an interesting arrangement of charged amino acid residues along the inner surface of the channel, resulting in the entry of water via its oxygen then flipping to lead with its hydrogens half way through the channel. How might this explain aquaporin's specificity for water and not cations or protons?

Water, being a small polar molecule, is able to interact with both negative and positive residues in the channel.

Several sweet potatoes were cut into identically sized cubes, weighed, and placed into open beakers with solutions of different sucrose (sugar) concentrations at 22∘C. After 24 hours, the cubes were blot dried and weighed again. The percent mass change of each potato was then determined and graphed. Use the straight line on the graph to calculate the water potential (in bars bars) of the sweet potato cells.

-17.2

Water potential is the tendency of water to move from one area to another, often due to osmosis. Osmosis occurs when there is solute that cannot cross a semi-permeable membrane such as the plasma membrane or the cell wall, forcing free water to move instead. A plant cell with Ψ P ΨP of 2 bars and an internal solute concentration of 0.3 M is submerged in an open container of 1M NaCl dissolved in water at 25∘C. (Assume the solute within the plant is starch, which does not ionize.) Calculate which water potential value determines the net movement of water.

-49.53 bar

Cells communicate in order to spur a variety of processes. There are many types of communication that cells rely on depending on the situation of the signal and the intended result. Regardless of the signaling type, the process results in a signal transduction cascade, as shown below. Which of the following statements provides the BEST example of a local signaling event?

A bacterial cell sends signaling molecules to bacteria in the nearby vicinity in order to maintain the population size.

Alzheimer's Disease (also called Alzheimer's Dementia) is a neurodegenerative disorder that predominantly affects individuals who are sixty-five years and older (though it is not limited exclusively to this age group). This disorder is characterized by anatomical and physiological changes to the brain that can produce symptoms such as mood changes, loss of memory, loss of language ability, etc. The changes in the brain of an individual with Alzheimer's disease can be seen in the image below. The image on the left depicts a normal brain, and the image on the right depicts the brain of an Alzheimer's patient. While the exact reason these changes take place is unknown, the physiological reasons behind the changes have been well documented. The two primary causes are the buildup of Tau protein tangles and Beta-Amyloid plaques. Tau proteins are generally found surrounding the microtubule structures of neurons. As the Tau proteins detach from the microtubules, not only do the microtubules depolymerize, thus exposing the neurons and causing them to be susceptible to damage, but the Tau proteins clump together, forming tangles (as seen in the image below) as well. The other cause of Alzheimer's Disease, Beta-Amyloid proteins plaques, are sections of integral cell membrane proteins (called Amyloid Precursor Proteins, or APP) that are often used in the signal transduction process. Many times, to stimulate signal transduction, a phosphorylation cascade is initiated. When APP in a normal patient is phosphorylated, intracellular signaling takes place. When the APP is phosphorylated in an individual who is predisposed to Alzheimer's Disease, the phosphorylation triggers an enzyme to snip off a portion known as Beta-Amyloid Protein (as seen below). The effects of this are two-fold. First, the neuron becomes incapable of performing basic signal transduction activities that may be crucial to the functioning of the brain. Second, the snippets of Beta-Amyloid protein form a mass known as a plaque that can further disrupt brain function. With respect to Tau proteins, which of the following off-label medications could potentially be useful to at least partially treat the effects of the Tau protein aspect of Alzheimer's Disease?

A drug that is predominantly used to prevent the recurrence of cancer.

Cell membranes are usually referred to as being "selectively permeable." This is due to the fact that they are able to determine which molecules are allowed into and out of the cell as well as the means by which they do so. Which of the following statements describes the use of a protein channel that would use active transport as a means to pass molecules through the membrane?

A proton pump uses ATP energy to move molecules from an area of low concentration inside the cell to an area of high concentration outside of the cell.

Adrenaline (also known as epinephrine) is a signaling molecule that can have multiple effects on cells depending on the type of receptor to which it binds. Many times, adrenaline is associated with "fight or flight" responses, implying that this molecule readies the body to survive during life-threatening events. Though the original precursor for adrenaline synthesis is the amino acid L-Tyrosine, an intermediate metabolite of L-Tyrosine is the neurotransmitter called dopamine. Dopamine is then converted into adrenaline through the use of the enzymes Dopamine β-hydroxylase and Phenylethanolamine N-Methyltransferase, as seen in the diagram below. Which of the following offers the MOST accurate prediction of what would happen to adrenaline levels if an individual's dopamine levels were higher than normal?

Adrenaline levels would stay the same as before.

Glucose is an important source of energy for all living organisms; however, the movement of glucose is a one-way process. For example, eating a candy bar increases the concentration of glucose in the gut. Through active transport, the glucose is transported into the intestinal cells and into the bloodstream. Which of the following predicts what would happen if glucose moved by facilitated diffusion instead?

As the gut empties, the concentration gradient changes and glucose would flow back into the gut. Energy reserves in the body would be depleted and probably result in death.

A student filled one dialysis bag with 0.1 M starch solution, and a second bag was filled with distilled water. The bags were then placed in separate beakers of 0.1 M starch solution. Dialysis bags model the selective permeability of cell membranes and allow very small molecules, ions and water to pass through according to the surrounding concentration gradient. Starch is too large a molecule to pass through the dialysis membrane. The student massed the bags every five minutes to monitor the amount of mass gained or lost by each bag over the course of 30 minutes. The percent change in mass for each bag was calculated and the data were plotted in the graph below: Which of the following lines on the graph would the student have obtained with the data from the bag containing a 0.1 M starch solution?

C

Like animals, plants also have hormones that are used for many signaling purposes. Perhaps the most famous plant hormone is ethylene, which participates in many plant processes. The most well-known of these is fruit ripening — signaling from the ethylene gas in a neighboring ripe banana is what causes a nearby avocado to ripen, for instance. The ethylene receptors signal in the absence of ethylene. These receptors activate the CTR1 protein kinase, which in turn suppresses the function of the protein EIN2. When ethylene does bind to its receptor, changes in the receptor's shape reduce the ability of CTR1 to supress EIN2. The result is the freeing of EIN2 to move into the nucleus and eventually allowing downstream transcription factors to accumulate in the nucleus. This ultimately allows the cell to regulate gene expression in response to the presence of ethylene. Which of the following phenotypes might one expect to observe in a plant that has a mutation in CTR1 such that it cannot be suppressed by the ethylene receptor?

CTR1 is usually active in the absence of ethylene. Because this mutation prevents the inactivation of CTR1 by ethylene, the activity of CTR1 continues regardless of the presence of ethylene and continuously prevents downstream transcription from taking place.

The cell membrane of a eukaryotic cell is selectively permeable, meaning that it allows some substances to cross it more easily than others. Which of the following substances are able to easily cross the cell membrane?

Carbon dioxide and oxygen gas.

An oak tree is growing in central New Hampshire. To survive, the plasma membranes of its cells must maintain a certain level of fluidity so as to allow the diffusion of various materials into and out of the cells. As the temperatures fluctuate from very hot to very cold between summer and winter, which of the following enables the tree to maintain appropriately permeable cell membranes?

Cells can add phospholipids with saturated fatty acid tails during hot weather.

In mammals, including humans, nitric oxide (NO) is an important cellular signaling molecule involved in many physiological processes. Research into its function led to the 1998 Nobel Prize for discovering its role in cardiovascular function. One specific role of nitric oxide in cardiac function is the dilation of blood vessels, a process called vasodilation. Vasodilation of the arteries lowers blood pressure and decreases the force that the heart muscle needs to exert to pump blood. The cell signaling mechanism begins when NO diffuses into the smooth muscle cells of the blood vessel and activates Guanylate Cyclase which, in turn, stimulates the Guanylate Cyclase to generate cyclic GMP (guanosine monophosphate) from Guanosine Triphosphate (GTP). Protein Kinase G phosphorylates several proteins that regulate calcium concentrations and, in this case, causes alterations in thin and thick muscle filaments that result in smooth muscle relaxation. This signaling mechanism is illustrated below: Signal transduction pathways are composed of a complex series of biochemical reactions and can be initiated two different ways. Which of the following statements BEST explains the primary function of each molecule involved in nitric oxide cell signaling?

Cyclic GMP is the second messenger that results in amplification of the signal via a phosphorylation cascade. The cellular response is smooth muscle relaxation.

A student filled three dialysis bags with different concentrations of a starch solution, and one bag was filled with distilled water. The bags were then placed in separate beakers of a 3.0 M starch solution. Dialysis bags model the selective permeability of cell membranes and allow very small molecules, ions and water to pass through according to the surrounding concentration gradient. Starch is too large a molecule to pass through the dialysis membrane. The student massed the bags every five minutes to monitor the amount of mass gained or lost by each bag over the course of 30 minutes. The percent change in mass for each bag was calculated, and the data were plotted in the graph below: Which of the following lines on the graph would the student have obtained with the data from the bag containing distilled water?

D

Ethylene gas is a plant hormone that regulates plant growth, development and response to environmental stress. It is produced from leaves,​ roots, stems, flowers and fruits, and it plays a major role in fruit ripening, flowering and abscission (the natural shedding of leaves, flowers and fruits). The biosynthesis of ethylene in plant cells occurs in a two-step biochemical pathway illustrated in Figure 2 below: Atta-Aly, Brecht and Huber (2000) researched ethylene feedback mechanisms in tomato and strawberry fruit tissues. Their studies revealed that immature fruit had a reduced concentration of ACC when exposed to ethylene gas, but ethylene application on mature fruit increased ACC oxidase (ACO) activity. Which of the following statements BEST explains how different plant tissues respond to ethylene gas?

Ethylene gas serves as a negative feedback signal in immature fruit and a positive feedback signal in mature fruit.

The human circulatory system uses blood as a medium for transporting nutrients and assisting with the removal of metabolic waste. Human blood contains red blood cells (erythrocytes) and white blood cells (leukocytes) suspended in a medium of plasma. While erythrocytes primarily distribute oxygen ( O 2) and remove carbon dioxide (CO2), erythrocytes must also transport solutes (e.g., organic and inorganic molecules) and water across their cell membrane. The translocation of molecules and ions across the cell's membrane ensure proper functioning of the cell. Plasma membranes are selectively permeable barriers that regulate chemical traffic using an array of transport mechanisms. Which of the following correctly describes the transport mechanism that the plasma membrane of erythrocytes utilize when regulating the movement of solutes or water?

Glucose is transported across the erythrocyte plasma membrane via a type of passive transport called facilitated diffusion.

Two key factors affect the genetic expression that ultimately determines an embryonic cell's fate, cytoplasmic segregation and external induction of neighboring stem cells. External induction is prevalent in vertebrate embryonic development. During the 1980s, a genus of closely studied amphibians, Xenopus, the clawed frogs, provided evidence of a major induction event to a group of biologists. They were able to witness the interaction between mesodermal and ectodermal layers in neural cell formation, soon followed by the activation of sodium pumps. Induction involves the release of inducer molecules from designated inducting anchor tissue to nearby responding tissue that then experiences a shift in cell differentiation. Inducer reception on the responding, or precursor cells, triggers a series of steps that direct a stem cell's new fate. During the Xenopus tissue induction experiments, biologists performed molecular assays in order to extract and identify molecular evidence of neural-specific gene transcripts. This was used to verify differentiation by induction was successful. Which of the following steps in cell induction would directly yield gene transcripts relevant to nerve cell properties?

Following induction, initiation of signal transduction cascade events inside a precursor cell results in the transcription of genes important for differentiated nerve cells.

The presence of ethylene gas causes fruits to ripen. As the fruit ripens, it produces increasing amounts of ethylene. An investigator placed fruit samples in sealed containers as shown in the table and left them for three days. At the end of the time period, the investigator used iodine to test for the presence of starch. Which of the following lists these in order from highest to lowest starch content?

Group 3, Group 2, Group 1.

During development, an embryo goes through millions of cell divisions controlled by a number of different types of chemical signals. Once differentiation of the cells has occurred, the organism will begin to take on the form of the eventual species being created. Once the basic pattern of the organism has been established, morphogenesis will continue and includes apoptosis. Apoptosis is the intentional destruction of a cell, as seen in the image below. Which of the following BEST describes the need for apoptosis for the development of human toes?

If apoptosis did not occur, humans would have webbed feet with no distinct digits.

Communication between bacteria cells is called quorum sensing, which allows certain bacteria to coordinate their gene expression according to the density of nearby bacteria cells. Bacteria that use quorum sensing produce signaling molecules called autoinducers that bind to specific receptors within the same species of bacteria. Reception of the autoinducer activates transcription of certain genes, including those for autoinducer synthesis, as illustrated in the figure below. Vibrio fisheri is a species of bioluminescent bacteria that produce light when their population density is high. In this case, the autoinducer is N-acylhomoserine lactone (AHL) and its receptor protein called LuxR. Which of the following statements is a valid scientific explanation for the absence of bioluminescence in low-density populations of Vibrio fisheri?

In small populations, diffusion of the autoinducer, AHL, reduces its concentration in the surroundings, so LuxR is not activated and gene expression for bioluminescence in Vibrio fisheri does not occur.

The main components which make up the lipid bilayer of the cell membrane and contain hydrophobic and hydrophilic regions lead to important properties of cell membranes, including selective permeability. Which of the following components indicated creates the unique hydrophobic and hydrophilic regions of the cell?

Phospholipids, which contain hydrophobic fatty acid tails.

In mammals, including humans, nitric oxide (NO) is an important cellular signaling molecule involved in many physiological processes. Research into its function led to the 1998 Nobel Prize for discovering its role in cardiovascular function. One specific role of nitric oxide in cardiac function is the dilation of blood vessels, a process called vasodilation. Vasodilation of the arteries lowers blood pressure and decreases the force that the heart muscle needs to exert to pump blood. The cell signaling mechanism begins when NO diffuses into the smooth muscle cells of the blood vessel and activates guanylate cyclase which, in turn, stimulates the guanylate cyclase to generate cyclic GMP (guanosine monophosphate) from guanosine triphosphate (GTP). Protein Kinase G phosphorylates several proteins that regulate calcium concentrations and, in this case, causes alterations in thin and thick muscle filaments that results in smooth muscle relaxation. This signaling mechanism is illustrated below: Research published by Gustafsson, Persson, and Moncada (1990) found that nitric oxide production in the lungs decreases immediately under acute hypoxia (low oxygen), which causes the pulmonary blood vessels to constrict. This, in turn, limits oxygen delivery to the lungs, heart, red blood cells and mitochondria. A study published in the journal Nature (Beall et al., 2001) examined chronically hypoxic, high-altitude populations of Tibetans and Bolivian Aymara, two countries almost halfway across the world from one other, and found that exhaled levels of nitric oxide were unusually high relative to a low-altitude reference sample from the United States. Which of the following is a likely conclusion that can be made with these findings?

Populations living at high altitudes have an adaptive mechanism to offset hypoxia since the elevated levels of nitric oxide in the lungs dilates pulmonary blood vessels, which increases oxygen delivery to the lungs, blood, and cells of the body.

Molecules use a variety of transport methods to enter and exit the cell depending on their polarity, concentration gradient, and size. Certain molecules may be able to use more than one transport method. Which of the following statements provides an accurate example of how one molecule may utilize multiple transport methods?

Sodium utilizes active transport with the sodium-potassium pump and facilitated diffusion with sodium channels.

Cancer is not a contagious disease; instead, it is an error in cellular regulation. Which of the following explains why cancer can spread so quickly throughout a living organism?

Some cancer cells can produce their own growth factor to pass cell cycle checkpoints.

Plants have tiny little projections from their roots called root hairs. These are labeled h in the image below. These specialized structures increase the surface area in order to increase the amount of water and nutrients that can be absorbed. In the colder months of the American Northeast, salt trucks will often be seen on the roads. Their purpose is to spread salt across the road surface to prevent icy road conditions. Often, there are plants lining these roads. Which of the following statements BEST predicts how the plants will be impacted by the increased amount of salt in the soil due to the salt trucks?

The added salt to the soil will make the solute concentration outside the plant greater than that inside the plant. As a result, water will not enter through the root hairs, and the plant will shrivel.

The signal transduction pathway is a form of cell communication. The regulation of glycogen metabolism functions via a signal transduction pathway and results in a cascade of reactions that are triggered by several hormones that promote the production of glucose. Which of the following provides an explanation for why the kidney is involved in the glycogen pathway?

The adrenal glands rest on top of the kidneys and contain epinephrine. Epinephrine signals a fight-or-flight response, which stimulates the liver to produce glucose.

Scientists in a lab are planning an experiment in order to determine what molecules can and cannot enter the plasma membrane. The group chooses two molecules that are frequently transported across the membrane. They radioactively tag potassium ions with fluorescent pink dye. Oxygen is radioactively tagged with fluorescent blue dye. The scientists infuse a colony of cells with both oxygen and potassium in an environment that only supports simple diffusion and wait 5 minutes in order to allow transport to occur. Scientists then observed the solution in order to determine the ending locations of oxygen and potassium. Which of the following statements BEST describes the predicted results of the experiment explained above?

The cell colonies would appear blue, and the solution surrounding the cells would appear purple.

As shown in the image, a series of enzymes catalyze the reaction that changes Molecule A into Molecule C. Presence of Molecule C competitively inhibits the actions of Enzyme A. Which of the following is the MOST likely result of the presence of large amounts of Molecule C?

The concentration of Molecule B will decrease

The plasma membrane provides protection to the cell and controls what can and cannot enter and exit the cell. The plasma membrane is made up of phospholipids, shown in the figure below. Based on the figure above, which of the following BEST explains how the chemical structure of a phospholipid contributes to selective permeability?

The hydrophobic tails prevent large quantities of water from entering the cell without a transport protein, whereas the tails allow large quantities of oxygen and carbon dioxide to enter.

To determine which apple variety, McIntosh or Honeycrisp, has a higher osmolarity, 24 24 uniform apple cores were made from each type. Three of each variety were initially massed and placed in beakers filled with 100 mL 100 mL of the respective solutions of sucrose:0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M. They were left overnight and massed again the following day. The graph below shows the percent change in mass of the cylinders in each solution of sucrose. Which of the following describes the intracellular osmotic potential of the Honeycrisp apple compared to the McIntosh apple?

The intracellular osmotic potential of the Honeycrisp apple compared to the McIntosh apple is hypertonic.

Cell membranes are usually referred to as being "selectively permeable." This is due to the fact that they are able to determine what molecules are allowed into and out of the cell as well as the means in which they do so. Which of the following would be an appropriate explanation for how the cell membrane has these selectively permeable properties?

The phospholipid bilayer is comprised of lipids that are hydrophilic at one end and hydrophobic at the other. Large, polar molecules are not allowed through the bilayer, but small polar and non-polar molecules are.

In humans, kidneys function to remove metabolic waste materials and other toxins from the blood stream while simultaneously recovering key electrolytes and water from the filtrate. The functional cells of the kidney are called nephrons. Portions of the nephron called the Loops of Henle create a concentration gradient within the kidney for the purposes of osmoregulation. Which of the following is a structural difference between cells of the descending Loop of Henle and cells of the ascending Loop of Henle that aids in conservation of water?

The plasma membranes of cells in the ascending loop have fewer aquaporins than do the plasma membranes of cells in the descending loop.

Potato cells typically have an osmolarity between 0.4 M and 0.46 M. Potato cores with an osmolarity of 0.5 M are placed in a 1.0 M solution of sucrose water overnight. Which of the following BEST predicts the result of the above protocol?

The potato cores will lose mass.

Molecules are able to pass through the plasma membrane using a number of different transport methods. The concentration gradient, chemistry of the molecule, and amount of molecule all determine the method of transport most frequently taken. The figure below shows one method of cell transport. Based on the figure, which of the following statements accurately describes the method of transport and the evidence that contributes to that identification?

The transport method shown is facilitated diffusion because the molecules in the diagram are moving from a high concentration to a low concentration without the use of energy and with the help of a channel protein.

Cell communication is important for the appropriate coordination of systems in all multicellular organisms. There are four major types of cell signaling, as seen below. This does not include synaptic signaling, which occurs between neurons and uses neurotransmitters. Which of the following statements BEST describes why this feature is conserved in all animals?

There needs to be a way for signals to be received by some cells and not by others. Some signals will be able to pass through the cells while others will not. This specificity has led to diversity.

Ethylene gas is a plant hormone that regulates plant growth, development and response to environmental stress. It is produced from leaves,​ roots, stems, flowers and fruits, and it plays a major role in fruit ripening, flowering and abscission (the natural shedding of leaves, flowers, and fruits). Like many hormones, ethylene functions via an intracellular signal transduction pathway, illustrated in Figure 1 below: In the absence of ethylene gas, a receptor protein activates the CTR1 protein kinase, which represses EIN2 function. Recent studies with plants genetically engineered to have reduced gene expression of an ethylene receptor (Tieman et al., 1999) showed an increase in ethylene sensitivity, including accelerated fruit ripening and flower aging. Which of the following statements BEST explains how the ethylene response is regulated in plants?

This pathway involves negative regulation by ethylene receptor proteins (3) because CTR1 (5) actively represses the release of EIN2 (6) in the absence of ethylene (1), but the response is activated when ethylene (1) is present or when the number of ethylene receptors (3) is reduced.