Unit Progress checks

Which of the following best describes the process that adds a monosaccharide to an existing polysaccharide?

A specific enzyme removes the hydrogen ( H ) from the monosaccharide and the hydroxide ( OH ) from the polysaccharide, creating a bond between the two and creating a water ( H2O ) molecule.

In vascular plants, water flows from root to leaf via specialized cells called xylem. Xylem cells are hollow cells stacked together like a straw. A student explains that evaporation of water from the leaf pulls water up from the roots through the xylem, as shown in Figure 1. Which statement describes how water is pulled up through the xylem to the leaves of the plant?

As water exits the leaf, hydrogen bonding between water molecules pulls more water up from below.

Figure 1 represents a segment of DNA. Radiation can damage the nucleotides in a DNA molecule. To repair some types of damage, a single nucleotide can be removed from a DNA molecule and replaced with an undamaged nucleotide. Which of the four labeled bonds in Figure 1 could be broken to remove and replace the cytosine nucleotide without affecting the biological information coded in the DNA molecule?

Bonds Y and Z at the same time

Which of the following would most likely occur if cattle lost the ability to maintain a colony of microorganisms in their digestive tract?

Cattle would no longer be able to use cellulose as a primary source of glucose.

A student wants to modify model 1 so that it represents an RNA double helix instead of a DNA double helix. Of the following possible changes, which would be most effective in making model 1 look more like RNA than DNA?

Changing the deoxyribose's to ribose's by adding −OH groups

Some viral infections can lead to the rupture of the lysosome membrane. Which prediction of the effect of this disruption of cellular compartmentalization is most likely correct?

Hydrolytic enzymes will be released, which will cause cell death.

Which of the following is common feature of the illustrated reactions showing the linking of monomers to form macromolecules?

Monomers are joined by a covalent bond, and a water molecule is produced.

Intravenous (IV) therapy is used for fluid replacement in instances of dehydration in humans and other animals. One type of IV fluid is essentially a saltwater solution. To determine the best concentration for therapy in people, a team of students is researching the effects of solutions of different salt concentrations on red blood cells. The following observations were made from three different red blood cell samples viewed under a microscope. 0.3% Saline (Cells swell) 0.9% Saline (Cells unchanged) 1.5% Saline (Cells shrink) The team wants to extend the research project. What should the team of students do next to obtain data that are more conclusive?

Repeat the process with other salt concentrations.

Which of the following describes a key difference among the 20 amino acids that are used to make proteins?

Some amino acids are hydrophobic.

A group of mutations, known as MT-ND1, have been identified in mitochondrial DNA. These mutations are associated with a number of debilitating diseases stemming from the production of nonfunctional proteins in the mitochondria. Which of the following cellular deficiencies would most likely be related to these MT-ND1 mutations?

The cell is unable to complete reactions related to electron transport and ATP production.

Different polysaccharides are used by plants for energy storage and structural support. The molecular structures for two common polysaccharides are shown in Figure 1. Starch is used by plants for energy storage, and cellulose provides structural support for cell walls. The monomer used to construct both molecules is glucose. Based the information provided, which of the following statements best describes why starch and cellulose provide different functions in plants?

The differences in the assembly and organization of the monomers of these two polymers result in different chemical properties.

The figure shows the results of an experiment to investigate the effects of an enriched CO2 environment on plant growth. Identical plants were separated into different groups and grown either in a standard CO2 environment (400 ppm CO2) or in an enriched CO2 environment (700 ppm CO2). Of the plants in each environment, half were grown under ideal conditions and half were grown under stressed conditions. Based on the figure, which statement best describes the observed relationship between atmospheric CO2 enrichment and plant growth under ideal and stressed conditions?

The increase in atmospheric CO2 resulted in a greater increase in plant growth under stressed conditions than under ideal conditions.

Gaucher disease is an inherited disorder in which cells of the body are unable to break down a particular type of lipid, resulting in a buildup of the lipid in some tissues and organs. Based on the information provided, Gaucher disease results most directly from a defect in the function of which of the following organelles?

The lysosome

Phosphorous (P) is an important nutrient for plant growth. Figure 1 shows Arabidopsis thaliana plants grown under phosphorus‐sufficient (left) and phosphorus‐starved (right) conditions for six weeks. Which of the following is the most likely reason for the difference in leaf growth?

The phosphorus-starved plant was unable to synthesize both the required nucleic acids and lipids, limiting growth.

A certain type of specialized cell contains an unusually large amount of rough endoplasmic reticulum (ER). Which of the following functions is this cell type most likely specialized to perform?

The production and secretion of proteins

A researcher claims that the incorporation of carbon dioxide into organic molecules during photosynthesis does not violate the second law of thermodynamics. Which of the following statements best helps justify the researcher's claim?

The total system that includes photosynthetic organisms and the Sun becomes less ordered over time.

Which of the following transport mechanisms will be affected most directly by a temporary shortage of ATP molecules inside the cell?

The transport of glucose molecules against a concentration gradient

As shown in the diagram, when environmental temperatures drop below freezing, a layer of ice typically forms on the surface of bodies of freshwater such as lakes and rivers. Which of the following best describes how the structure of ice benefits the organisms that live in the water below?

The water molecules in ice are farther apart than those in liquid water, so the ice floats, maintaining the warmer, denser water at the lake bottom.

A researcher claims that budding yeast are able to survive in different environments because they produce enzymes that allow them to use different molecules as sources of matter and energy. Which of the following statements best helps justify the researcher's claim by providing a relevant example?

Yeast cells produce invertase, which is an enzyme that catalyzes the conversion of the disaccharide sucrose into glucose and fructose.

European flycatchers feed caterpillars to their hatchlings. Graph 1 shows the average dates of hatching and fledging (leaving the nest), and the biomass of the caterpillars between early May (when flycatcher young hatch) and June (when fledging of young occurs). Based on the data, scientists claim that the reproductive behavior of European flycatchers is influenced by the availability of energy sources. Which of the following statements best justifies this claim?

Young European flycatchers hatch from eggs when caterpillar biomass is available for the young birds to consume and convert into energy for growth.

Researchers investigate the transport of a certain protein into cells by endocytosis. In an experiment, the researchers incubate the cells in the presence of the protein and measure the amount of the protein that is absorbed into the cells over a five-minute period. Based on their observations, what should the researchers do to further clarify how the availability of the protein outside the cells affects the rate of endocytosis of the protein?

Incubate the cells in the presence of several different concentrations of the protein.

Testosterone is a small steroid hormone that is important in cell signaling. Which of the following indicates where testosterone enters a cell and why it is able to cross at that point?

1, because testosterone is nonpolar and can diffuse through the membrane.

A researcher proposes a model to explain how enzyme-substrate interactions determine enzyme specificity. The model is based on the idea that substrate molecules form favorable interactions with the amino acid side chains in an enzyme's active site. Based on the model, which of the following statements best explains an enzyme's specificity for a particular substrate molecule?

A molecule with negative charges interacts with positively charged side chains in the enzyme's active site.

A researcher claims that a certain herbicide suppresses plant growth by inhibiting chloroplast function. To test the claim, the researcher treats isolated chloroplasts with increasing concentrations of the herbicide. The data from the experiment are presented in Table 1. Herbicide Concentration (μg/L) pH Difference across Thylakoid Membrane ATP Production 0 3.5 Very high 2 2.5 Moderate 8 0.5 Very low 32 0 Very low Which of the following statements best clarifies how the data support the researcher's claim?

ATP synthase activity depends on a proton gradient across the thylakoid membrane.

A study was conducted to understand the factors controlling the rate at which molecules or ions travel across cell membranes. An artificial membrane was created that was composed of a phospholipid bilayer only. The speed at which various substances crossed this membrane was measured. Some substances can pass through an actual cell membrane much faster than they passed through the artificial membrane in this study. Which of the following statements best explains this finding?

Actual cell membranes have a variety of proteins embedded in the membrane that are absent in the artificial membrane.

Which of the following best describes a structural similarity between the two molecules shown in Figure 1 that is relevant to their function?

Both molecules contain nucleotides that form base pairs with other nucleotides, which allows each molecule to act as a template in the synthesis of other nucleic acid molecules.

A magnesium sulfate solution taken orally can cause a net movement of water into the large intestine, which results from water molecules diffusing through aquaporins embedded in the cells of the intestinal lining. By which of the following mechanisms do the water molecules most likely move into the large intestine?

By passive transport from an area of low osmolarity to an area of high osmolarity

Aldosterone (a steroid hormone) is a small, nonpolar, hydrophobic molecule that enters a target cell by moving across the plasma membrane, down a concentration gradient. Based on the information presented, how does aldosterone most likely enter target cells?

By simple diffusion

The cell membrane is selectively permeable due to its structure. Thus, the internal environment of the cell is distinct from the external environment of the cell. One biologist hypothesizes that small nonpolar molecules readily pass through the membrane. Another biologist alternatively hypothesizes that these types of molecules require channel and transport proteins that are embedded in the membrane in order to move across the membrane. Which of the following data would best refute this alternative hypothesis?

CO2 and N2 movement in and out of cells is unaffected when membrane protein activity is blocked.

Some cells, such as intestinal cells, exchange a lot of material with their surroundings. The surface-to-volume ratio of these cells affects the efficiency of material exchange. The table provides measurements of four different eukaryotic cells. Cell 1 2 3 4 Total surface area (μm2) 40 60 80 100 Total volume (μm3) 20 10 30 20 Based on the data, which cell is likely to be most effective in the exchange of materials?

Cell 2

Researchers have proposed a model of chloroplast evolution. According to the model, chloroplasts evolved from a small prokaryotic organism that was engulfed by an ancestral eukaryote. The engulfed prokaryote then formed an endosymbiotic relationship with the eukaryotic host. Which of the following observations best supports the model?

Chloroplasts and some prokaryotes share similar photosynthetic reactions.

A researcher claims that the initial rise of oxygen in Earth's early atmosphere, which occurred approximately 2.3 billion years ago, resulted from the metabolic activity of prokaryotic organisms. The claim is based on an interpretation of the geochemical and fossil evidence represented in Figure 1. Which of the following types of evidence will best support the researcher's claim?

Evidence that the cyanobacteria produced oxygen as a by-product of photosynthesis

Researchers investigated the effect of urea on the three-dimensional structure of a certain enzyme. The researchers dissolved the enzyme in an aqueous buffer solution and added urea to the solution. The enzyme did not appear to have a secondary or tertiary structure. The researchers carefully removed the urea from the solution and determined that the enzyme had the original secondary and tertiary structure again. Based on the results of the experiment, which of the following statements best predicts the effect of urea on the enzyme's function?

Function will be disrupted by adding the urea and regained by removing the urea.

Aminolevulinate dehydratase (ALAD) is an enzyme that relies on zinc as a coenzyme. A zinc ion binds to the ALAD active site, where it forms favorable interactions with the side chains of three amino acids. Researchers have found that substituting a lead ion for a zinc ion in the ALAD active site causes inhibition of ALAD. Which of the following statements best helps explain how the lead ion causes inhibition of ALAD?

It changes the three-dimensional structure of the active site so that ALAD is no longer compatible with its substrate.

In an experiment, researchers compared the growth of two different plants, plant X and plant Y. The researchers maintained the plants under nearly identical conditions and observed that plant X grew faster than plant Y. The researchers also observed that the inner mitochondrial membranes of plant X had more folds than did those of plant Y. Which of the following conclusions about increasing the number of folds in the inner mitochondrial membrane is best supported by the results of the experiment?

It increases the surface area available for ATP production, which results in faster cell growth.

Figure 1 shows a short segment of a double-stranded nucleic acid molecule. Which of the following statements is correct about the molecule shown in Figure 1 ?

It is DNA because of the nucleotides present.

Euglenids are single-cell eukaryotes that live in aquatic environments. The chloroplasts found inside euglenids are enveloped by three membranes, as represented in Figure 1. The inner membrane of euglenid chloroplasts resembles the thylakoid membrane. Which of the following claims about the origin of the euglenid chloroplast is best supported by the three-membrane structure of the envelope?

It originated from the incorporation of a photosynthetic prokaryote into a eukaryotic cell by two endosymbiotic events.

In an experiment, researchers provided a radiolabeled amino acid to living plant cells. After one hour, the researchers determined the amount of the radiolabeled amino acid that was in each of several subcellular compartments. The results of the experiment are represented in the table. RELATIVE AMOUNTS OF RADIOLABELED AMINO ACID: Nucleus 2.1, Mitochondria 2.7, Endoplasmic 1.9, Reticulum Cytosol 1 Which of the following conclusions about the radiolabeled amino acid is best supported by the results of the experiment?

It was mostly incorporated into proteins that regulate and manage metabolic reactions.

Pectinase is a protein that catalyzes the breakdown of pectic polysaccharides in plant cell walls. A researcher designs an experiment to investigate the effect of salinity on the ability of pectinase to lower the activation energy of the reaction involved. The design of the experiment is presented in Table 1. For each test tube, the researcher will measure the amount of product formed over 20 minutes. Test Tube Sodium Chloride Concentration (molar) Temperature (degrees C) Substrate Added Pectinase Added 1 0 23 Yes No 2 0 23 Yes Yes 3 0.5 23 Yes No 4 0.5 23 Yes Yes 5 1.0 23 Yes No 6 1.0 23 Yes Yes 7 1.5 23 Yes No 8 1.5 23 Yes Yes Which of the following statements best helps justify the inclusion of test tube 5 in the experiment?

It will act as a control for test tube 6 by showing the effect of the presence or absence of the enzyme.

A researcher designs an experiment to investigate whether soil bacteria trigger the synthesis of defense enzymes in plant roots. The design of the experiment is presented in Table 1. For each group in the experiment, the researcher will determine the average rate of change in the amount of defense enzymes in the roots of the seedlings. Group Number of Seedlings Type of Soil Treatment Solution 1 10 Sterile potting soil Contains actively reproducing soil bacteria 2 10 Sterile potting soil Contains heat-killed soil bacteria 3 10 Sterile potting soil Contains no soil bacteria Which of the following statements best helps justify the inclusion of group 2 as one of the controls in the experiment?

It will show whether the changes observed in group 1 depend on the metabolic activity of soil bacteria.

Which of the following observations best supports the claim that mitochondria evolved from once-free-living prokaryotic cells by the process of endocytosis?

Mitochondria are surrounded by a double membrane.

Researchers investigated the influence of environmental pH on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different pH. The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at 23°C. The results of the experiment are represented in Figure 1. The figure presents a line graph in the coordinate plane. The horizontal axis is labeled p H, and the numbers 0 through 14, in increments of 2, are indicated. The vertical axis is labeled Relative Activity, and no numbers are indicated along it, although the axis ends in an arrowhead. The line begins at the point p H 0 with 0 relative activity, and moves horizontally to the right to p H 1 and 0 relative activity. The line then slants upwards and to the right at a constant rate until p H 2, then slants sharply upwards and to the right at a fairly constant rate until its peak at p H 5. The line then slants sharply downwards and to the right at a constant rate until p H 6, where the relative activity is half that of the peak. The line continues to slant sharply downwards and to the right at a constant rate until p H 7, where the relative activity is one tenth that of the peak. The line then slants less sharply downwards, and to the right at a constant rate until p H 9, where the relative activity is almost 0. The line then slants slightly downwards and to the right at an extremely low constant rate until p H 12 and p H 14, where relative activity drops to 0. Figure 1. The effect of pH on peroxidase activity Based on Figure 1, which of the following statements best predicts the effect that a change from a moderately acidic environment (pH near 6) to a basic environment will have on peroxidase activity?

Peroxidase activity will decrease.

Based on the figure, which of the following statements best describes the relationship between regions 1 and 2 of the protein?

Region 1 is hydrophilic because it interacts with an aqueous environment, whereas region 2 is hydrophobic because it interacts with the interior of the membrane.

Researchers investigated the influence of environmental pH on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different pH. The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at 23°C. The results of the experiment are represented in Figure 1. The figure presents a line graph in the coordinate plane. The horizontal axis is labeled p H, and the numbers 0 through 14, in increments of 2, are indicated. The vertical axis is labeled Relative Activity, and no numbers are indicated along it, although the axis ends in an arrowhead. The line begins at the point p H 0 with 0 relative activity, and moves horizontally to the right to p H 1 and 0 relative activity. The line then slants upwards and to the right at a constant rate until p H 2, then slants sharply upwards and to the right at a fairly constant rate until its peak at p H 5. The line then slants sharply downwards and to the right at a constant rate until p H 6, where the relative activity is half that of the peak. The line continues to slant sharply downwards and to the right at a constant rate until p H 7, where the relative activity is one tenth that of the peak. The line then slants less sharply downwards, and to the right at a constant rate until p H 9, where the relative activity is almost 0. The line then slants slightly downwards and to the right at an extremely low constant rate until p H 12 and p H 14, where relative activity drops to 0. Figure 1. The effect of pH on peroxidase activity Which of the following actions will provide a negative control for the investigation?

Repeating the experiment using heat-denatured peroxidase

A researcher claims that genetic variation provides organisms with the ability to survive and reproduce in different environments. To support the claim, the researcher makes the following observation: bacteria that contain plasmids (small DNA molecules) are resistant to a wider range of antibiotics than are bacteria that contain no plasmids. Which of the following statements best establishes a connection between the observation and the researcher's claim?

Some plasmids contain antibiotic resistance genes

Different polysaccharides are used by plants for energy storage and structural support. The molecular structures for two common polysaccharides are shown in Figure 1. Starch is used by plants for energy storage, and cellulose provides structural support for cell walls. The monomer used to construct both molecules is glucose. A study determined the effect of two different digestive enzymes, A and B, on these two polysaccharides. Table 1 presents the data from the study. Mammals do not produce digestive enzyme B. However, sheep and cattle are two types of mammals that contain microorganisms in their digestive tract that produce enzyme B. Based on Figure 1, which of the following best compares the atomic structures of starch and cellulose?

Starch and cellulose are composed of repeating glucose monomers; however, in cellulose every other glucose monomer is rotated 180 degrees.

A student designs an experiment to investigate the influence of temperature on enzyme function. The student's plan is presented in Table 1. Test Tube Substrate Added Enzyme Added Temperature (°C) 1 Yes No 10 2 Yes Yes 10 3 Yes No 20 4 Yes Yes 20 5 Yes No 30 6 Yes Yes 30 7 Yes No 40 8 Yes Yes 40 Which test tubes are controls in the experiment?

Test tubes 1, 3, 5, and 7

Some membrane proteins help maintain the concentrations of ions inside a cell by transporting the ions across the cell's plasma membrane. Other membrane proteins form pores in the plasma membrane through which the ions can diffuse. A model showing the influence of membrane proteins on the movement of sodium (Na+) and potassium (K+) ions across a plasma membrane is presented in Figure 1. Based on the model presented in Figure 1, which of the following changes will most likely result from a depletion of available ATP stores inside the cell?

The Na+ concentration inside the cell will increase.

Figure 1 shows three amino acids that are part of a polypeptide chain. Figure 2 shows the same section of the chain after a mutation has occurred. How might this change affect the structure and function of the protein?

The R-group of the new amino acid, valine, has different chemical properties than the R-group of cysteine. This will cause the protein to misfold and not function properly in the cell.

A polypeptide is polymer of amino acids held together by peptide bonds. The process of dehydration synthesis creates these peptide bonds, as shown in Figure 1. As shown in Figure 1, an amino acid must have which of the following properties in order to be incorporated into a polypeptide?

The ability to form a covalent bond with both its NH2 group and its COOH group

Acetylcholinesterase (AChE) is a protein that catalyzes the conversion of acetylcholine to acetate and choline. When the concentration of AChE in an aqueous solution is held constant, the rate of the reaction catalyzed by AChE increases with increasing concentrations of substrate. At low concentrations of acetylcholine, a small increase in the substrate concentration results in a large increase in the reaction rate. At high concentrations of acetylcholine, however, a large increase in the substrate concentration results in only a small increase in the reaction rate. Which of the following statements correctly explains the observed effect of the acetylcholine concentration on the rate of the enzyme-catalyzed reaction?

The active site of AChE is specific for acetylcholine, and only one substrate molecule can occupy the active site at a time.

Phycobiliproteins are a complex of accessory pigments and proteins found in cyanobacteria but not in green algae. A researcher claims that the phycobiliprotein pigments in cyanobacteria allow the cyanobacteria to survive in certain aquatic niches better than green algae can. Which of the following statements best justifies the researcher's claim?

The additional pigments absorb light at wavelengths that green algae cannot absorb; this may allow cyanobacteria to capture more light energy for photosynthesis than green algae can in certain areas.

In an experiment, a researcher prepares a reaction mixture by dissolving a substance in a buffered solution. The substance is the substrate of a certain enzyme. The researcher adds a small amount of the enzyme to the reaction mixture and measures the amount of product that is formed over time. The data are represented in Figure 1. The figure presents the graph of a curve in the first quadrant of the coordinate plane. The horizontal axis is labeled Time, and no numbers are indicated along it. The vertical axis is labeled Amount of Product, and no numbers are indicated along it. Both axes end with arrowheads. The curve begins at the intersection of the 2 axes, then moves upwards and to the right at about a 45 degree angle. The curve then levels off, becoming approximately horizontal as it moves to the right. A point indicated about two thirds of the way along the horizontal region of the curve is labeled Add More Substrate. Figure 1. The amount of product formed by an enzyme-catalyzed reaction over time Which of the following best predicts the immediate result of adding more substrate to the reaction mixture at the point indicated by the arrow in Figure 1?

The amount of product will increase until the reaction reaches its equilibrium point or until the substrate is used up by the reaction.

Researchers investigated the influence of environmental pH on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different pH. The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at 23°C. The results of the experiment are represented in Figure 1. The figure presents a line graph in the coordinate plane. The horizontal axis is labeled p H, and the numbers 0 through 14, in increments of 2, are indicated. The vertical axis is labeled Relative Activity, and no numbers are indicated along it, although the axis ends in an arrowhead. The line begins at the point p H 0 with 0 relative activity, and moves horizontally to the right to p H 1 and 0 relative activity. The line then slants upwards and to the right at a constant rate until p H 2, then slants sharply upwards and to the right at a fairly constant rate until its peak at p H 5. The line then slants sharply downwards and to the right at a constant rate until p H 6, where the relative activity is half that of the peak. The line continues to slant sharply downwards and to the right at a constant rate until p H 7, where the relative activity is one tenth that of the peak. The line then slants less sharply downwards, and to the right at a constant rate until p H 9, where the relative activity is almost 0. The line then slants slightly downwards and to the right at an extremely low constant rate until p H 12 and p H 14, where relative activity drops to 0. Figure 1. The effect of pH on peroxidase activity One of the researchers proposes using oxygen gas production to measure reaction rates. Which of the following statements best justifies the use of the proposed modification as a way of creating an appropriate control for the investigation?

The experiment can be repeated without guaiacol, which will reveal the effect of guaiacol on the reaction rates.

A student is using dialysis bags to model the effects of changing solute concentrations on cells. The student places one dialysis bag that contains 25 mL of distilled water into each of two beakers that are filled with 200 mL of distilled water. (Figure 1). The membrane of each dialysis bag membrane contains pores that allow small solutes such as monoatomic ions to pass through but are too small for anything larger to pass. After 30 minutes, 5 mL of a concentrated solution of albumin (a medium-sized, water-soluble protein) is added to one of the two beakers. Nothing is added to the other beaker. After two more hours at room temperature, the mass of each bag is determined. There is no change in the mass of the dialysis bag in the beaker to which no albumin was added. Which of the graphs below best represents the predicted change in mass over time of the dialysis bag in the beaker to which albumin was added? Which of the graphs below best represents the predicted change in mass over time of the dialysis bag in the beaker to which albumin was added?

The figure presents a graph in the coordinate plane. The horizontal axis is labeled Time, in minutes, and the numbers 0 through 150, in increments of 30, are indicated. The vertical axis is labeled Relative Mass of Dialysis Bag. The axis has an arrowhead at the top end, and no numbers are indicated along it. The graphed line begins at 0 minutes, about halfway up the vertical axis, and extends horizontally to the right until 30 minutes. A label indicates Albumin Added at 30 minutes. The graphed line starts to move downward and to the right at 30 minutes until it ends at 150 minutes, just above the horizontal axis.

Two competing hypotheses exist regarding the cell membrane structure. One hypothesis states that membrane structure is static and membrane components throughout the bilayer are rigidly bound. Alternatively, the other hypothesis states that cell membranes are a fluid mosaic in which membrane components may drift within the bilayer around the surface of the cell. An experiment is set up in which membrane proteins of two different cells are fluorescently labeled with two different colors and then fused as shown in Figure 1. Which of the following results, one hour after membrane fusion, best supports the alternative hypothesis that the cell membrane is a fluid mosaic?

The figure presents a model of a cell. The membrane of the cell has both grey proteins and black proteins embedded in it. The grey proteins and black proteins are distributed throughout the cell membrane, and are not concentrated in particular areas.

Which feature of model 1 best illustrates how biological information is coded in a DNA molecule?

The linear sequence of the base pairs

Lysosomes digest food particles brought into a cell by endocytosis. After a vesicle containing food particles fuses with a lysosome, H+ ions are transported into the lysosome from the cytosol. This significantly lowers the pH of the lysosome relative to the cytosol and activates the enzymes that digest the particles. Which of the following best predicts what will happen to the lysosomal enzymes if the proteins that transport H+ ions from the cytosol into the lysosome are damaged?

The lysosomal enzymes will not become active, since there will be no active transport of H+ ions.

Stomata are pores on the surfaces of the leaves and stems of plants that regulate gas exchange between the plants and the atmosphere. Researchers found that the stomata density on the leaves of a species of plant change as the concentration of CO2 in the atmosphere changes. When grown at 350 ppm CO2 the plant has an average density of 300 stomata per mm2, but when grown at 400 ppm CO2 the plant has an average density of 250 stomata per mm2. Which of the following best describes how the ratio of the density of stomata (stomata per mm2) per CO2 concentration (ppm CO2) changes as the CO2 concentration increases?

The ratio decreases from 0.86 to 0.63 , because fewer stomata are needed at higher CO2 concentrations.

Hereditary spherocytosis (HS) is a disorder of red blood cells that causes the cells to be smaller and spherical instead of having the usual flattened, biconcave shape. The average diameter of normal red blood cells is 7.2μm, and the average diameter of red blood cells in a person with HS was found to be 6.7μm. The normal red blood cell has an average surface area of 136μm2 and an average volume of 91μm3. Which of the following provides an accurate calculation of the surface area to volume ratio of an HS red blood cell, as well as a prediction of its effect on the efficient transferring of oxygen compared to a normal red blood cell?

The ratio is 0.89 , and the cells are less efficient at transferring oxygen.

A scientist is studying the various prokaryotic and eukaryotic species found floating in a sample of water taken from a marine ecosystem. Which cellular component will be found in the widest range of organisms in the sample?

The ribosome, since all organisms need to synthesize proteins.

Brown fat is a type of fat tissue found in hibernating mammals. Inside the mitochondria of these fat tissue cells, these mammals have an uncoupling protein embedded in the inner mitochondrial membrane. This uncoupling protein allows hydrogen ions to leak from the intermembrane space back into the mitochondrial matrix. Figure 1 shows details of the processes in the inner mitochondrial membrane. Which of the following statements provides reasoning that supports the claim that brown fatty tissue keeps an animal warm?

The uncoupling protein in this tissue reduces the proton gradient across the membrane and thus produces heat to warm the animal without ATP production

Researchers conducted an experiment to investigate the effects of a valinomycin treatment on skeletal muscle cells. Valinomycin is a naturally occurring substance that can be used as a drug. The results of the experiment are presented in the table. Relative Rates of ATP Production Time after Treatment Untreated Cells Valinomycin-Treated Cells 5 minutes 1.0 0.3 10 minutes 7.7 2.7 Which of the following claims about the effects of the valinomycin treatment is best supported by the data presented in the table?

The valinomycin treatment caused a decrease in the activity of the mitochondria.

Certain bacteria can use both ethyl alcohol and acetate as sources of nutrients. In an experiment where both nutrients are available to a bacterial population, the following results were obtained and graphed. What additional procedure would best help determine whether these movements are due to active transport or to passive transport?

Use two additional treatments, one containing only ethyl alcohol and one containing only acetate. Include a substance known to block ATPATP use by the plasma membrane. Compare the graphs of these two treatments to the original graph.

Beetroot cells contain a family of dark red pigments called betalains. The selectively permeable nature of the beetroot cells keeps the internal environment of the cell separate from the external environment of the cell. Researchers are interested in determining whether the selective permeability of beetroot cells is due to the cell membrane or if it is due to the cell wall. Exposure to cellulase is known to damage the structure of the cell wall. An experiment is set up in which beetroot cells are placed in an aqueous solution with cellulase and in one without cellulase. Which of the following results best refutes the alternative hypothesis that selective permeability is a consequence of the cell wall?

When beetroot cells are placed in a solution with cellulase, the solution remains clear.

Catalase is an enzyme found in yeast cells that facilitates the chemical breakdown of hydrogen peroxide to water and oxygen gas. An experiment was conducted to determine the effect of pH on catalase function. Five buffer solutions of varying pH (2, 4, 6, 8, and 10) were prepared and added to separate test tubes. Hydrogen peroxide (H2O2) was added to each test tube. Yeast was added, and the reactions were timed. After 1 minute the amount of oxygen gas released was determined by measuring the foam layer produced in each test tube. Figure 1 illustrates the experimental setup. A set of five additional test tubes were prepared and used as controls. Which of the following best describes the contents expected to be contained in one of the five control test tubes?

pH 4 buffer solution and hydrogen peroxide only

Scientists are testing substance L to determine how it enters mammalian cells in a culture. The cells maintain a 120 millimolar (mM) intracellular concentration of substance L . The scientists determined the rate of entry of substance L into the cells at various external concentrations of substance L (10 to 100 mM) in culture medium (Table 1). (a) Identify the most likely mode of transport across the membrane for substance L. Explain how information provided helps determine the most likely mode of transport. (b) On the axes provided, construct an appropriately labeled line graph with correct scale and units to illustrate the data in Table 1. The figure presents a grid with 10 by 10 axes. (c) Determine the external concentration of substance L that will result in one-half of the maximal entry rate. (d) Predict the likely effect on the ability of substance L to enter the cells if substance L is attached to a large protein instead of free in the culture.

a) The response indicates that substance L most likely crosses the membrane by active transport. The response indicates that the cells maintain an intracellular concentration of 120 mM , which is always greater than the concentration of substance L in the culture medium. b) N/A c)The response indicates that the external concentration of substance L that will result in one-half of the maximal entry rate is between 31 mM and 34 mM . d)The response indicates that substance L will be unable to enter the cells if it is attached to a large protein OR the response indicates that substance L will be unable to enter the cells if it is attached to a large protein unless there is a specific cell membrane receptor for the protein.

Figure 1 represents a plasma membrane and molecules present on either side. (a) Describe the biological need for cells to be surrounded by a membrane that is selectively permeable for different materials. (b) Explain how the model shows selective permeability of the membrane to specific ions. (c) Describe the characteristics of the phospholipid bilayer that permit small hydrophobic lipid molecules to pass directly across the membrane. (d) Based on the model, explain whether the molecules shown crossing the membrane require energy to do so.

a)The response indicates that a cell membrane separates the internal environment of the cell from the external environment OR that a cell membrane that is selectively permeable can help to regulate what molecules move between the differing environments inside and outside of a cell. b)The response indicates that a membrane channel protein is selective for a specific kind of ion because only one of the two kinds of ion represented can pass through the channel. The response also indicates that ions cannot simply cross directly between the phospholipids of the membrane (although a small lipid-soluble molecule can). c)The response indicates that the interior of a phospholipid bilayer is hydrophobic, which allows small hydrophobic molecules to diffuse across the membrane. d)The response does not indicate that energy is not required for the substances to cross the membrane because the substances are being passively transported from a region of higher concentration to a region of lower concentration.

Enolase is an enzyme that catalyzes one reaction in glycolysis in all organisms that carry out this process. The amino acid sequence of enolase is similar but not identical in the organisms. Researchers purified enolase from Saccharomyces cerevisiae, a single-celled eukaryotic yeast that grows best at 37°C, and from Chloroflexus aurantiacus, a bacterium that grows best at the much higher temperature of 55°C. The researchers compared the activity of purified enolase from the two organisms by measuring the rate of the reaction in the presence of varying concentrations of substrate and a constant amount of each enzyme at both 37°C and 55°C. (a) Depending on the organism, the optimal pH for enolase to catalyze its reaction is between 6.5 and 8.0. Describe how a pH below or above this range is likely to affect enolase and its catalytic ability. (b) Identify the appropriate negative control the researchers most likely used when measuring the reaction rate in the presence of each organism's enolase. (c) The researchers predict that for any particular concentration of substrate, the C. aurantiacus enolase-catalyzed reaction is more rapid at 55°C than at 37°C. Provide reasoning to justify the researchers' prediction.

a)The response indicates that a pH below or above this range will most likely cause enolase to denature/change its shape and be less efficient or unable to catalyze the reaction. b) The response indicates that the appropriate negative control is to measure the reaction rate (at the varying substrate concentrations) without any enzyme present. c)The response indicates that the enolase has a more stable/functional/correct/normal protein structure at the higher temperature of 55°C than at 37°C because the enzyme is from an organism that is adapted to growth at 55°C .

White blood cells called B cells produce proteins that can be used for the treatment of certain illnesses. However, these B cells do not live for very long on their own. To keep the B cells growing for a long time in laboratories, scientists fuse the B cells with cancer cells (fused B-cancer cells) that do grow for a very long time. The particular cancer cells used for the fusion are treated with chemicals that make them unable to produce the nitrogenous bases adenine and guanine, but the B cells with which they are fused do produce these nitrogenous bases. The scientists grow the large fused B-cancer cells in a growth medium that contains necessary nutrients for the cells and includes a source of carbon. (a) Describe the role of carbon in biological systems. (b) The membranes of both B cells and the cancer cells are largely composed of phospholipids. Explain how, when the membranes are fused, the polar parts of the phospholipids from one cell will interact with the phospholipids from the other cell and how the nonpolar parts of the phospholipids from one cell will interact with the phospholipids from the other cell. (c) Make a claim about the most immediate effect on the fused B-cancer cells if the fused cells are transferred to a growth medium that lacks a source of nitrogen. (d) Provide reasoning with evidence based on the composition of biological macromolecules to support your claim.

a)The response indicates that carbon is used to build biological macromolecules such as carbohydrates, proteins, nucleic acids, and lipids. b)The response indicates that the polar part of the phospholipids from one cell will align or interact with the polar parts of the phospholipids from the other cell, and nonpolar parts of the phospholipids from one cell will align or interact with nonpolar parts of the phospholipids from the other cell. c)The response indicates that the cells will die OR that they will be unable to synthesize DNA and RNA/nucleic acids/nucleotides and amino acids/polypeptides/proteins. d)The response indicates that nucleic acids ( DNA , RNA , or nucleotides) and amino acids (polypeptides, or proteins) contain nitrogen.

Researchers studied the relationship between glucose concentration, oxygen level, and ATP production in one type of mammalian cell. Cells were isolated and cultured in growth medium containing either 1.5⁢mM glucose or 25 mM glucose and at oxygen levels that varied from 0% to 21%. The researchers determined the concentration of ATP per cell under the different conditions. The ATP concentrations are shown as relative to the maximum ATP concentration obtained when cells were cultured in the presence of 25 mM glucose and 21% oxygen, standard culture conditions. The data are shown in Table 1. (a) Describe the role of oxygen in cellular respiration. (b) Using the template, construct an appropriately labeled graph to represent the data in Table 1. The figure presents an empty 25 by 15 grid. (c) Describe the relationship between the concentration of glucose in the culture medium and the ATP concentration in the cells. (d) In a further experiment, the researchers add a compound to the cell growth medium that both binds and releases protons (H+) and also passes through lipid membranes. Predict the effect of this added compound on ATP production by the cells. Justify your prediction.

a)The response indicates that oxygen is the terminal acceptor of electrons that have passed through the electron transport chain. b)N/A c)The response indicates that the concentration of glucose appears to have little or no effect on the ATP concentration in the cells. d) The response indicates that the amount of ATP produced will decrease OR that no ATP will be produced. The response does not indicate that the compound is more likely to bind protons where the protons are in greater concentration, in the intermembrane space. It also does not indicate that if the compound then carries the protons across the inner membrane to the matrix, there will no longer be a proton concentration/pH/electrochemical gradient across the inner membrane, and protons will not flow through and power the ATP synthase enzymes.

Scientists are studying the structure and function of Receptor X, a single-polypeptide protein that is found in the membrane around certain types of cells. Receptor X contains no alpha-helices or beta sheets. A specific molecule outside the cells is recognized and bound by Receptor X. The binding of the molecule to Receptor X causes the cells to have a particular response. To study the structure and function of Receptor X, the scientists are altering the sequence of small sections of the receptor. Both the normal sequence of a five‑amino acid section of Receptor X and an altered sequence that contains two amino acid substitutions are shown in Figure 1. (a) Identify the process used to form the covalent peptide bonds that join amino acids into a polypeptide. (b) The change in the amino acid sequence illustrated in Figure 1 caused a change in the shape of Receptor X. Based on the R groups of the original and substituted amino acids, explain why Receptor X changed shape. (c) Using the template below that represents the four levels of protein structure, place an X on each level that is expected to be altered as a result of the amino acid substitutions shown in Figure 1. d) Explain how the amino acid substitution shown in Figure 1 is most likely to affect the function of Receptor X.

a)The response indicates that the process that joins amino acids into a polypeptide is a dehydration synthesis OR a condensation reaction. b)The response indicates that two amino acids with charged or ionic or hydrophilic R-groups were replaced by two amino acids with uncharged or nonpolar or hydrophobic R-groups. c) The response indicates primary structure and tertiary structure. d)The response indicates that because function is determined by shape, the function of receptor X is likely to change OR the structural change might alter the binding of the molecule to receptor X OR the structural change might alter the ability of receptor X to cause a cellular response.