BIO PPCS

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?

Phosphorus is used to make nucleic acids and certain lipids. Without phosphorus atoms, nucleic acids and lipids cannot be made for the plant to use for growth

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

Without the enzyme BB produced by microorganisms in their digestive tract, cellulose would pass through the digestive tract without being digested.

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.

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

A specific enzyme removes the hydrogen (HH) from the monosaccharide and the hydroxide (OHOH) from the polysaccharide, creating a bond between the two and creating a water (H2OH2O) molecule.

Which of the following statements best describes the different functions of starch and cellulose in plants?

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

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

Based on the figure, which statement best describes the observed relationship between atmospheric CO2CO2 enrichment and plant growth under ideal and stressed conditions?

The increase in atmospheric CO2CO2 resulted in a greater increase in plant growth under stressed conditions than under ideal conditions.

Figure 1 represents a segment of DNADNA. Radiation can damage the nucleotides in a DNADNA molecule. To repair some types of damage, a single nucleotide can be removed from a DNADNA 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 DNADNA molecule?

Bonds Y and Z at the same time

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

Changing the deoxyriboses to riboses by adding −OH−OH group

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

The linear sequence of the base pairs

As shown in Figure 1, an amino acid must have which of the following properties in order to be incorporated into a polypeptide?

An R-groupR-group that is compatible with the R-groupR-group of the last amino acid incorporated

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 DNADNA because of the nucleotides present.

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

Some amino acids are hydrophobic.

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.

Water molecules are polar covalent molecules. There is a partial negative charge near the oxygen atom and partial positive charges near the hydrogen atoms due to the uneven distribution of electrons between the atoms, which results in the formation of hydrogen bonds between water molecules. The polarity of water molecules contributes to many properties of water that are important for biological processes.

Which of the following models best demonstrates the arrangement of hydrogen bonds between adjacent water molecules?

The hydrogen bonds between these water molecules correctly show the attractive force between the hydrogen atom of one water molecule and the oxygen atom of the adjacent water 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.

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.

The three-membrane structure of the chloroplast envelope best supports the claim presented in this answer choice. The three-membrane structure most likely resulted from two endosymbiotic events, with the middle membrane originating from the first event and the outer membrane originating from the second event.

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.

Lysosomes digest food particles brought into a cell by endocytosis. After a vesicle containing food particles fuses with a lysosome, H+H+ ions are transported into the lysosome from the cytosol. This significantly lowers the pHpH 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+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+H+ ions.

Since the pHpH of the lysosome has to become lower than that of the cytosol, active transport is needed to move H+H+ ions into the lysosome, against the H+H+ ion concentration gradient, to activate the enzymes.

Hereditary spherocytosis (HS)(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 7.2μm7.2μm, and the average diameter of red blood cells in a person with HSHS was found to be 6.7μm6.7μm. The normal red blood cell has an average surface area of 136μm2136μm2 and an average volume of 91μm391μm3.

Which of the following provides an accurate calculation of the surface area to volume ratio of an HSHS 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 0.890.89, and the cells are less efficient at transferring oxygen

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.

Chloroplasts and some prokaryotes share similar photosynthetic reactions.

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.

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.

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?

CO2CO2 and N2N2 movement in and out of cells is unaffected when membrane protein activity is blocked.

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 ATP use by the plasma membrane. Compare the graphs of these two treatments to the original graph.

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

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

The transport of glucose molecules against a concentration gradient

A certain type of specialized cell contains an unusually large amount of rough endoplasmic reticulum (ER)(ER).

Which of the following functions is this cell type most likely specialized to perform?

The production and secretion of proteins

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.

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.

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.

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

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.

Based on the data, which cell is likely to be most effective in the exchange of materials?

Cell 2

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

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

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.

The figure shows a representation of a protein embedded in a cell membrane. The numbers indicate different structural regions of the protein.

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.

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.

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 because aldersterone can enter a cell by moving across the plasma membrane and moving down the concentration gradient.

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.

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.

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.

Which of the following cellular deficiencies would most likely be related to mutations in mitochondrial proteins?

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

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?

lysosome

Intravenous (IV)(IV) therapy is used for fluid replacement in instances of dehydration in humans and other animals. One type of IVIV 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.

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.

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.

Based on Figure 1, which of the following statements best predicts the effect that a change from a moderately acidic environment (pHpH near 6) to a basic environment will have on peroxidase activity?

Peroxidase activity will decrease

Which of the following actions will provide a negative control for the investigation?

Repeating the experiment using heat-denatured peroxidase

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.

Aminolevulinate dehydratase (ALAD) is an enzyme that relies on zinc as a cofactor. 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.

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.

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.