AP Biology Unit 1 Multiple Choice

Which of the following correctly illustrates a dipeptide and an amino acid in the optimal position to form a tripeptide?

A

Which of the following best describes the structures of carbohydrates? A They only occur as disaccharides. B They occur as monomers, chains of monomers, and branched structures. C They only occur as long and branched structures. D They occur as chains of monomers that hydrogen bond with complementary chains of monomers.

B They occur as monomers, chains of monomers, and branched structures.

Ultraviolet (UV) radiation can damage DNA by breaking weak bonds. Which of the following best explains how this occurs? A UV radiation disrupts the double helix structure by breaking the covalent bonds between the nitrogenous base pairs. B UV radiation disrupts the double helix structure by breaking the hydrogen bonds between the nitrogenous base pairs. C UV radiation is able to break DNA strands in two by breaking covalent bonds between the sugar-phosphate backbone molecules. D UV radiation is able to break DNA strands in two by breaking hydrogen bonds between the sugar-phosphate backbone molecules.

B UV radiation disrupts the double helix structure by breaking the hydrogen bonds between the nitrogenous base pairs.

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?

D

High levels of certain plant nutrients in runoff can lead to rapid growth of algae (an algal bloom) in aquatic ecosystems. These algal blooms are generally followed by algal death and decomposition, which consumes large amounts of dissolved oxygen in the water and results in oxygen levels insufficient to support aerobic respiration. This process is known as eutrophication. The amount of algae present in a body of water can be estimated from the amount of chlorophyll a in a sample of the water. A researcher studying eutrophication collected samples at different times of the year in a freshwater ecosystem. The samples were analyzed for total nitrogen and chlorophyll a concentration (Figure 1) as well as total phosphorus and chlorophyll a concentration (Figure 2). Which of the following best explains how higher concentrations of nitrogen and phosphorus contribute to eutrophication? A An increase in the population of algae results in more nitrogen and phosphorus in the water, causing severe eutrophication. B Both bacteria and algae require nitrogen and phosphorus, so the algae must grow faster to compete with bacteria. C Nitrogen and phosphorus stimulate oxidative phosphorylation, which consumes the available oxygen in the water. D Algae require nitrogen and phosphorus to build macromolecules, so higher concentrations of these nutrients can result in algal blooms.

D Algae require nitrogen and phosphorus to build macromolecules, so higher concentrations of these nutrients can result in algal blooms.

Which of the following is most directly responsible for water's unique properties? A It contains oxygen atoms. B It contains hydrogen atoms. C It is an ionic compound. D It forms hydrogen bonds.

D It forms hydrogen bonds.

If 30% of the nucleotides in a single-stranded RNA molecule are adenine, then what percent are expected to be thymine? A 0% B 20% C 30% D 70%

A 0%

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? A As water exits the leaf, hydrogen bonding between water molecules pulls more water up from below. B As water exits the leaf, signals are sent to the roots to pump more water up to the leaves through the xylem by adhesion. C Evaporation from the leaf decreases the hydrogen bonds that form between the water molecules in the xylem, which helps the water molecules to be pulled up the xylem. D Evaporation of water from the leaf increases the hydrogen bonds that form between water molecules in the air, providing the energy for transport.

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

A common test for liver function involves sprinkling sulfur powder onto a sample of urine (mostly water with dissolved bodily waste). Sulfur powder sprinkled on a sample from an individual with impaired liver function will sink because the urine contains a high level of bile salts, while the sulfur powder sprinkled on normal urine samples will float. Which of the following best explains why bile salts cause the sulfur powder to sink? A Bile salts decrease the surface tension of the urine sample. B Bile salts increase the water potential of the urine. C Bile salts increase the density of the urine sample. D Bile salts decrease the strength of the covalent bonds within a water molecule.

A Bile salts decrease the surface tension of the urine sample.

Which of the following best explains why a cell's plasma membrane is composed of two layers of phospholipids rather than just a single layer? A Having two oppositely oriented layers of phospholipids allows only the hydrophilic heads to interact with water inside and outside of the cell. B Having two oppositely oriented layers of phospholipids allows the hydrophilic heads to repel water both inside and outside of the cells. C Having two identically oriented layers of phospholipids gives cells more protection from the exterior environment than just a single layer would. D Having two identically oriented layers of phospholipids allows for the production of vacuoles while still maintaining a protective barrier.

A Having two oppositely oriented layers of phospholipids allows only the hydrophilic heads to interact with water inside and outside of the cell.

A typical bag of fertilizer contains high levels of nitrogen, phosphorus, and potassium but trace amounts of magnesium and calcium. Which of the following best matches the fertilizer component with the molecule in which it will be incorporated by organisms in the area? A Nitrogen will be incorporated into nucleic acids. B Phosphorus will be incorporated into amino acids. C Potassium will be incorporated into lipids. D Magnesium will be incorporated into carbohydrates.

A Nitrogen will be incorporated into nucleic acids.

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? A 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. B The new amino acid, valine, has replaced cysteine in the new protein. Since the number of amino acids has remained the same, there will be no change in the three-dimensional folding, or function, of the protein. C Since this is a linear section, it does not influence protein folding. Thus, there will be no change in protein structure or function. D Since the new amino acid is bounded on one side by an amino acid with a negatively charged R-group and by an amino acid on the other side with a positively charged R-group, the charges will balance and the protein will fold as usual.

A 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.

Which of the following statements best describes the different functions of starch and cellulose in plants? A The differences in the assembly and organization of the monomers of these two polymers result in different chemical properties. B Since starch and cellulose are composed of identical monomers, the cellular environment where they are located controls their function. C The monomers of cellulose are connected by covalent bonds, making it idea for structural support. D The monomers of starch are connected by ionic bonds, making it ideal for energy storage for plants.

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

A culture of Spirogyra (an autotrophic alga) is maintained in a water solution containing dissolved carbon dioxide and a source of phosphates but lacking nitrogen compounds. A researcher determines the rates of synthesis of several organic compounds found in the Spirogyra before and after several weeks in the water solution. Which of the following graphs best illustrates a likely result of the experiment?

B

Amylase is an enzyme that converts carbohydrate polymers into monomers. Glycogen synthase is one of the enzymes involved in converting carbohydrate monomers into polymers. Which of the following best explains the reactions of these enzymes? A Amylase aids in the removal of a water molecule to break covalent bonds whereas glycogen synthase aids in the addition of a water molecule to form covalent bonds. B Amylase aids in the addition of a water molecule to break covalent bonds whereas glycogen synthase aids in the removal of a water molecule to form covalent bonds. C Amylase aids in the addition of a water molecule to form covalent bonds whereas glycogen synthase aids in the removal of a water molecule to break covalent bonds. D Amylase aids in the removal of a water molecule to form covalent bonds whereas glycogen synthase aids in the addition of a water molecule to break covalent bonds.

B Amylase aids in the addition of a water molecule to break covalent bonds whereas glycogen synthase aids in the removal of a water molecule to form covalent bonds.

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? A Changing the sequence of the base pairs B Changing the deoxyriboses to riboses by adding −OH groups C Changing the shapes of the nitrogenous bases to match those shown in model 2 D Changing the sugar-phosphate backbone to a ribbon, as shown in model 3

B Changing the deoxyriboses to riboses by adding −OH groups

Which of the following statements best describes how organisms such as rabbits obtain the carbon necessary for building biological molecules? A Rabbits eat plants and use energy absorbed from the plants to make carbon atoms from electrons, protons, and neutrons in the air. B Rabbits eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules. C Rabbits eat plants and use water absorbed from the plants to hydrolyze CO2, which the rabbits breathe in from the air and use as a carbon source. D Rabbits eat plants and make carbon-containing molecules by using carbon atoms that the plants absorbed from the soil and stored in the cells of their leaves.

B Rabbits eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules.

A student analyzed a viral genome and found that the genome had the following nucleotide composition. • 28% adenine • 20% thymine • 35% cytosine • 17% guanine Which of the following best describes the structure of the viral genome? A Double-stranded DNA B Single-stranded DNA C Double-stranded RNA D Single-stranded RNA

B Single-stranded DNA

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 on Figure 1, which of the following best compares the atomic structures of starch and cellulose? A Starch is composed of carbon, hydrogen, and oxygen, while cellulose also contains nitrogen. B Starch and cellulose are composed of repeating glucose monomers; however, in cellulose every other glucose monomer is rotated 180 degrees. C Starch is composed of monomers that each have a CH2OH group, while cellulose only has a CH2OH group on every other monomer. D Starch and cellulose are composed of identical monomers and therefore have identical structures.

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

DNA and RNA are nucleic acids that can store biological information based on the sequence of their nucleotide monomers. Which of the following best describes a structural difference between DNA and RNA? A DNA contains four types of nitrogenous bases, whereas RNA contains only two types of nitrogenous bases. B The backbone of DNA contains deoxyribose, whereas the backbone of RNA contains ribose. C A DNA molecule is composed of two parallel strands with the same 5′ to 3′ directionality, whereas an RNA molecule is composed of only one 5′ to 3′ strand. D Phosphate groups provide rigidity to DNA, but RNA is flexible and contains no phosphate groups.

B The backbone of DNA contains deoxyribose, whereas the backbone of RNA contains ribose.

Researchers compared similar proteins from related organisms in different habitats. They found that the proteins from organisms living in harsh environments had a greater number of cysteine amino acids than did proteins from organisms not living in harsh environments. The structure of cysteine is shown. Bonds can form between the sulfur atom of different cysteine amino acids (S-S bonds). Figure 1. Chemical structure of cysteine Which of the following best describes the effect of a greater number of cysteine amino acids on the stability of the proteins? A The change has no effect on the stability of the protein because only one type of amino acid is involved. B The change leads to increased protein stability because of an increased number of S-S bonds in the tertiary structure of the proteins. C The change leads to decreased protein stability because of an increased number of S-S bonds in the tertiary structure of the proteins. D The change leads to increased protein stability only when the added cysteine amino acids are next to other cysteine amino acids in the primary structure.

B The change leads to increased protein stability because of an increased number of S-S bonds in the tertiary structure of the proteins.

Figure 1 represents a nucleic acid fragment that is made up of four nucleotides linked together in a chain. Which of the following characteristics of Figure 1 best shows that the fragment is RNA and not DNA? A The 5′ to 3′ orientation of the nucleotide chain B The identity of each nitrogenous base C The charges on the phosphate groups D The type of bond linking the nucleotides together

B The identity of each nitrogenous base

Which of the following best describes how amino acids affect the tertiary structure of a protein? A The number of amino acids determines the tertiary structure of the protein. B The interactions of the different R-groups with other R-groups and with their environment determine the tertiary structure of the protein. C The R-group of the last amino acid that is added to a growing polypeptide chain determines the next amino acid that is added to the chain. D The sequence of the amino acids in the polypeptide chain determines the protein's primary structure but has no effect on its tertiary structure.

B The interactions of the different R-groups with other R-groups and with their environment determine the tertiary structure of the protein.

Water and ammonia interact to form hydrogen bonds, as represented in the figure. Which statement best helps explain the formation of the hydrogen bond represented in the figure? A The oxygen has a partial positive charge, and the nitrogen has a partial negative charge. B The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge. C The hydrogen attached to the oxygen has a partial negative charge, and the nitrogen also has a partial negative charge. D The nitrogen has a partial positive charge, and the hydrogen attached to the oxygen also has a partial positive charge.

B The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge.

A mutation in the gene coding for a single-polypeptide enzyme results in the substitution of the amino acid serine, which has a polar R group, by the amino acid phenylalanine, which has a nonpolar R group. When researchers test the catalysis of the normal enzyme and the mutated enzyme, they find that the mutated enzyme has much lower activity than the normal enzyme does. Which of the following most likely explains how the amino acid substitution has resulted in decreased catalytic activity by the mutated enzyme? A The substitution decreased the mass of the enzyme so that the mutated enzyme binds more weakly to the substrate than the normal enzyme does. B The substitution altered the secondary and tertiary structure of the enzyme so that the mutated enzyme folds into a different shape than the normal enzyme does. C The substitution caused many copies of the mutated enzyme to cluster together and compete for substrate to bind. D The substitution caused the directionality of the enzyme to change such that the amino terminus of the normal enzyme has become the carboxy terminus of the mutated enzyme.

B The substitution altered the secondary and tertiary structure of the enzyme so that the mutated enzyme folds into a different shape than the normal enzyme does.

Students investigated the effect of light on the carbon cycle in aquatic ecosystems by performing the controlled experiment summarized below. The students placed equal amounts of water ( pH 7.0 ) from a large aquarium in glass beakers. The students transferred aquatic plants from the aquarium to several of the beakers, and then they placed equal numbers of the beakers in the light or the dark (Figure 1: groups I and II ). Similarly, the students transferred goldfish from the same aquarium to other beakers, and then they placed equal numbers of those beakers in the light or dark (Figure 1: groups III and IV ). Finally, the students placed an equal number of beakers containing water only in the light or dark (Figure 1: groups V and VI ). After exposing the samples to light or dark for one hour, the students recorded the pH of the water in each beaker. Carbon dioxide dissolved in water will lower the pH of an aqueous solution. In the experiment, the students used changes in pH to monitor changes in the amount of carbon dioxide in the water. For each treatment group, the students calculated the mean pH and standard error, as documented in the table below. Which of the following graphs is the most appropriate representation of the experimental results documented in the table?

B- answer with bar graph

Students conducted a controlled experiment to investigate whether sawdust provides enough nutrients to support plant growth. The students separated ten nearly identical sunflower seedlings into two groups. They grew the seedlings in the first group in potting soil and the seedlings in the second group in sawdust composed mostly of cellulose. After twenty days, the students recorded observations about the seedlings in each group. The students' observations are presented in the table. Treatment Group Mean Seedling Height Observations Seedlings in potting soil 18.5 cm The leaves have a dark green color and are normal in size. Seedlings in sawdust 4.8 cm The leaves have a grayish color and are small in size. The observed differences between the groups most likely resulted from differences in the ability of the seedlings to produce which of the following monomers?

C

Which of the following best describes the formation of the bond shown in Figure 1 ? A An ionic bond is formed between a carbon atom of one amino acid and the nitrogen atom of the other amino acid. B An ionic bond is formed when the negative charge of an OH group is balanced by the positive charge of a hydrogen ion. C A covalent bond is formed between a carbon atom and a nitrogen atom along with the formation of H2O . D A covalent bond is formed that replaces the hydrogen bond between the OH group and the H atom.

C A covalent bond is formed between a carbon atom and a nitrogen atom along with the formation of H2O .

Which of the following best describes the process that adds a monosaccharide to an existing polysaccharide? A The monosaccharide is completely broken down by a specific enzyme and then the atoms are reorganized and made into a polysaccharide. B Ionic bonds are formed between adjacent carbon atoms of the monosaccharide and the polysaccharide by adding water (H2O) and a specific enzyme. C 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. D A specific enzyme removes two hydroxides (OH), one from the monosaccharide, and one from the polysaccharide, creating a bond between the two monosaccharides and creating a hydrogen peroxide (H2O2) molecule.

C 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.

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? A Bond X only B Bond W only C Bonds Y and Z at the same time D Bonds W and Z at the same time

C Bonds Y and Z at the same time

Figure 1. Molecule 1 represents RNA, and molecule 2 represents DNA. Which of the following best describes a structural similarity between the two molecules shown in Figure 1 that is relevant to their function? A Both molecules are composed of the same four nucleotides, which allows each molecule to be produced from the same pool of available nucleotides. B Both molecules are composed of the same type of five-carbon sugar, which allows each molecule to act as a building block for the production of polysaccharides. C 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. D Both molecules contain nitrogenous bases and phosphate groups, which allows each molecule to be used as a monomer in the synthesis of proteins and lipids.

C 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.

Bacteriophages are viruses that infect bacteria. In an experiment, bacteriophages were labeled with either radioactive phosphorus or radioactive sulfur. The labeled bacteriophages were incubated with bacteria for a brief amount of time and then removed. The infected bacteria cells were found to contain significant amounts of radioactive phosphorus but not radioactive sulfur. Based on the results of the experiment, which of the following types of molecules did the bacteriophages most likely inject into the bacteria cells? A Simple carbohydrate B Amino acid C DNA D Polypeptide

C DNA

Which of the following best describes the process by which gas from the atmosphere is obtained by plants and used to build lipids? A Gas is fixed by plants as part of the sulfur cycle. B Gas is fixed by plants as part of the nitrogen cycle. C Gas is directly obtained by plants as part of the carbon cycle. D Gas is directly obtained by plants as part of the magnesium cycle.

C Gas is directly obtained by plants as part of the carbon cycle.

Which of the following is responsible for the cohesive property of water? A Hydrogen bonds between the oxygen atoms of two adjacent water molecules B Covalent bonds between the hydrogen atoms of two adjacent water molecules C Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule D Covalent bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule E Hydrogen bonds between water molecules and other types of molecules

C Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule

Which of the following is common feature of the illustrated reactions showing the linking of monomers to form macromolecules? A Two identical monomers are joined by a covalent bond. B Two different monomers are joined by a covalent bond. C Monomers are joined by a covalent bond, and a water molecule is produced. D Monomers are joined by ionic bonds, and a water molecule is produced.

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

The molecular structures of linoleic acid and palmitic acid, two naturally occurring substances, are shown in the figure. Based on the molecular structures shown in the figure, which molecule is likely to be solid at room temperature? A Linoleic acid, because the absence of carbon-carbon double bonds allows the molecules to pack closely together. B Linoleic acid, because the presence of carbon-carbon double bonds prevents the molecules from packing closely together. C Palmitic acid, because the absence of carbon-carbon double bonds allows the molecules to pack closely together. D Palmitic acid, because the presence of carbon-carbon double bonds prevents the molecules from packing closely together.

C Palmitic acid, because the absence of carbon-carbon double bonds allows the molecules to pack closely together.

The sequences for two short fragments of DNA are shown above. Which of the following is one way in which these two segments would differ? A Segment 1 would not code for mRNA because both strands have T, a base not found in RNA. B Segment 1 would be more soluble in water than segment 2 because it has more phosphate groups. C Segment 1 would become denatured at a lower temperature than would segment 2 because A-T base pairs have two hydrogen bonds whereas G-C base pairs have three. D Segment 1 must be from a prokaryote because it has predominantly A-T base pairs.

C Segment 1 would become denatured at a lower temperature than would segment 2 because A-T base pairs have two hydrogen bonds whereas G-C base pairs have three.

Which of the following describes a key difference among the 20 amino acids that are used to make proteins? A Only some amino acids have an R-group. B Only some amino acids have a carboxyl group (COOH). C Some amino acids are hydrophobic. D Some amino acids contain the element phosphorus.

C Some amino acids are hydrophobic.

Which of the following best describes the hydrolysis of carbohydrates? A The removal of a water molecule breaks a covalent bond between sugar monomers. B The removal of a water molecule forms a covalent bond between sugar monomers. C The addition of a water molecule breaks a covalent bond between sugar monomers. D The addition of a water molecule forms a covalent bond between sugar monomers.

C The addition of a water molecule breaks a covalent bond between sugar monomers.

The carbohydrates glucose, galactose, and fructose have the same chemical formula (C6H12O6) but different structural formulas, as represented in the figure. Which of the following statements about glucose, galactose, and fructose is most likely true? A The carbohydrates have the same properties because they have the same number of carbon, hydrogen, and oxygen atoms. B The carbohydrates have the same properties because they each have a single carbon-oxygen double bond. C The carbohydrates have different properties because they have different arrangements of carbon, hydrogen, and oxygen atoms. D The carbohydrates have different properties because they have different numbers of carbon-carbon bonds.

C The carbohydrates have different properties because they have different arrangements of carbon, hydrogen, and oxygen atoms.

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? A The increase in atmospheric CO2 had no observable effect on plant growth under either ideal or stressed conditions. B The increase in atmospheric CO2 resulted in a greater increase in plant growth under ideal conditions than under stressed conditions. C The increase in atmospheric CO2 resulted in a greater increase in plant growth under stressed conditions than under ideal conditions. D The increase in atmospheric CO2 resulted in an inhibition of plant growth under both ideal and stressed conditions.

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

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? A The phosphorus-starved plant was unable to synthesize both the required proteins and lipids, limiting growth. B The phosphorus-starved plant was unable to synthesize both the required proteins and carbohydrates, limiting growth. C The phosphorus-starved plant was unable to synthesize both the required nucleic acids and lipids, limiting growth. D The phosphorus-starved plant was unable to synthesize both the required carbohydrates and nucleic acids, limiting growth.

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

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? A The water molecules in ice are closer together than those in liquid water, so the ice prevents the passage of air to the water, maintaining a constant gas mixture in the water. B The water molecules in ice are closer together than those in liquid water, so the ice forms a barrier that protects the organisms in the water from the freezing air temperatures. C 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. D The water molecules in ice are farther apart than those in liquid water, so the ice floats, preventing the escape of gases from the liquid water.

C 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.

Which of the following would most likely occur if cattle lost the ability to maintain a colony of microorganisms in their digestive tract? A Cattle would no longer be able to synthesize cellulose. B Cattle would have to convert cellulose to starch before digesting it. C Cattle would have to start producing enzyme B without the help of the bacteria. D Cattle would no longer be able to use cellulose as a primary source of glucose.

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

Figure 1 is a diagram of water molecules at the air-water interface at the surface of a pond. Based on Figure 1, which of the following best describes how the properties of water at an air-water interface enable an insect to walk on the water's surface? A Covalent bonds between water molecules and the air above provide cohesion, which causes tiny bubbles to form under the feet of the insect. B Ionic bonds between molecules at the surface of the water provide an electric charge, which attracts the feet of the insect, keeping it on the surface. C Polar covalent bonds between molecules at the surface of the water provide adhesion, which supports the weight of the insect. D Hydrogen bonds between molecules at the surface of the water provide surface tension, which allows the water surface to deform but not break under the insect.

D Hydrogen bonds between molecules at the surface of the water provide surface tension, which allows the water surface to deform but not break under the insect.

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 ? A It is RNA because of the relative direction of the two strands. B It is RNA because of the number of different nucleotides found in the molecule. C It is DNA because of the nature of the hydrogen bonds between guanine and cytosine. D It is DNA because of the nucleotides present.

D It is DNA because of the nucleotides present.

Polypeptides are continuously being formed and degraded. One of these processes is shown. Which statement is the most accurate description of the reaction shown in Figure 1? A It represents monomers linked by dehydration synthesis. B It represents a polypeptide chain that folds to form the tertiary structure. C It represents a polypeptide chain that is denatured into the primary structure. D It represents a polypeptide chain that is broken down through a hydrolysis reaction.

D It represents a polypeptide chain that is broken down through a hydrolysis reaction.

The CFTR protein is made up of 1,480 amino acids linked together in a chain. Some humans produce a version of the CFTR protein in which phenylalanine (an amino acid) has been deleted from position 508 of the amino acid chain. Which of the following best predicts how the amino acid deletion will affect the structure of the CFTR protein? A It will have no observable effect on the structure of the CFTR protein. B It will affect the primary structure of the CFTR protein, but the other levels of protein structure will not be affected. C It will affect the secondary and tertiary structures of the CFTR protein, but the primary structure will not be affected. D It will affect the primary, secondary, and tertiary structures of the CFTR protein.

D It will affect the primary, secondary, and tertiary structures of the CFTR protein.

Which of the following conclusions is most clearly supported by the representations of nucleic acid #1 and nucleic acid #2 ? A Nucleic acid #1 contains only purines, whereas nucleic acid #2 contains only pyrimidines. B Nucleic acid #1 contains the sugar ribose, whereas nucleic acid #2 contains the sugar deoxyribose. C Nucleic acid #1 contains positively charged phosphate groups, whereas nucleic acid #2 does not. D Nucleic acid #1 contains adenine-thymine base pairs, whereas nucleic acid #2 does not.

D Nucleic acid #1 contains adenine-thymine base pairs, whereas nucleic acid #2 does not.

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? A The ability to remain stable in the presence of water molecules B An R-group that is compatible with the R-group of the last amino acid incorporated C A central carbon atom that reacts with a nitrogen atom to form the peptide bond D The ability to form a covalent bond with both its NH2 group and its COOH group

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

The figure shows a model of the exchange of matter between the organisms that live together in an aquarium. The model includes matter exchange between plants, fish, and bacteria. The bacteria are represented as rod-shaped organisms living in the gravel at the bottom of the aquarium. Which of the following statements best describes how molecules released by the fish become nutrients for the plants? A The carbon dioxide molecules released by the fish are converted by the bacteria to oxygen atoms, which are used by the plants to make water molecules. B The oxygen molecules released by the fish are converted by the bacteria to ammonia molecules, which are used by the plants to make lipids and fatty acids. C The nitrites released by the fish are converted by the bacteria to carbon dioxide molecules, which are used by the plants to make carbohydrates. D The ammonia molecules released by the fish are converted by the bacteria to nitrates, which are used by the plants to make proteins and nucleic acids.

D The ammonia molecules released by the fish are converted by the bacteria to nitrates, which are used by the plants to make proteins and nucleic acids.

Which of the following is an accurate description of the process shown in Figure 1 ? A The linking of amino acids with an ionic bond as an initial step in the protein synthesis process B The formation of a more complex carbohydrate with the covalent bonding of two simple sugars C The hydrolysis of amino acids with the breaking of covalent bonds with the release of water D The formation of a covalent peptide bond in a dehydration synthesis reaction

D The formation of a covalent peptide bond in a dehydration synthesis reaction

Which feature of model 1 best illustrates how biological information is coded in a DNA molecule? A The 5′ and 3′ labels at the ends of each strand B The labeling of the hydrogen bonds between base pairs C The lines connecting sugars and phosphate groups that represent covalent bonds D The linear sequence of the base pairs

D The linear sequence of the base pairs

The diagram shows how water can adhere to the xylem in the stems of plants, which contributes to water movement in the plant. Which of the following best explains how water is able to move upward from the roots of a plant, through its xylem in the stem, and out to the leaves? A Water is polar, and the walls of the xylem are nonpolar. Water molecules have the ability to form hydrogen bonds with one another but not with the xylem walls. B Water is nonpolar, and the walls of the xylem are polar. Water molecules are able to form hydrogen bonds with the xylem walls, and they are pulled up the xylem. C Water and the xylem are both nonpolar. Water molecules have the ability to form hydrogen bonds with one another but not with the xylem walls. D Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.

D Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.

The synthesis of protein or carbohydrate polymers always produces which of the following as a byproduct? A ATP B Oxygen C Carbon dioxide D Urea E Water

E Water