AP Biology test
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 OHOH 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 H2OH2O . D. A covalent bond is formed that replaces the hydrogen bond between the OHOH group and the HH atom.
C. A covalent bond is formed between a carbon atom and a nitrogen atom along with the formation of H2OH2O . Correct. Even though the water molecule that is produced is not shown in Figure 1, it shows the formation of the peptide bond and the missing HH and OHOH.
A small protein is composed of 110 amino acids linked together in a chain. As shown in Figure 1, the first and last five amino acids in the chain are hydrophobic (have nonpolar and uncharged R-groups), whereas the remaining 100 amino acids are hydrophilic (have charged or polar R-groups). The nature of the R-group determines if the amino acid is hydrophobic or hydrophilic. A mutation results in the production of a version of the small protein that is only 105 amino acids long, as shown in Figure 2. Five of the hydrophobic amino acids are missing from one end of the chain. Which of the following best depicts the tertiary structures of the two proteins in water? The diagrams in the options are not drawn to the same scale as those in Figure 1 and Figure 2.
A. Correct. The hydrophilic middle of the protein chain would be attracted to the water molecules, and the hydrophobic ends would be repelled. Hydrophobic portions of proteins in water tend to be found near the center of the tertiary structure, as far from the water as possible.
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 CO2CO2, 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. Correct. Rabbits break down the plant molecules to obtain the individual atoms or small molecules that can be built into larger, complex biological molecules.
Figure 1. Nucleic acid segments DNA and RNA are nucleic acids that can store biological information based on the sequence of their nucleotide monomers. Figure 1 shows a short segment of each of the two types of nucleic acids. 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′5′ to 3′3′ directionality, whereas an RNA molecule is composed of only one 5′5′ to 3′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. Correct. The backbones of DNA and RNA are composed of an alternating sugar and base. In DNA, the sugar is deoxyribose, whereas the sugar in RNA is 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). 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-SS-S bonds in the tertiary structure of the proteins. C. The change leads to decreased protein stability because of an increased number of S-SS-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-SS-S bonds in the tertiary structure of the proteins. Correct. An increased number of S-SS-S bonds are possible with the addition of more cysteine in the proteins. The S-SS-S covalent bonds should add more structural stability to the proteins.
Figure 1 represents a nucleic acid fragment that is made up of four nucleotides linked together in a chain. Figure 1. Nucleic acid fragment Which of the following characteristics of Figure 1 best shows that the fragment is RNA and not DNA? A. The 5′5′ to 3′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 Correct. RNA contains uracil, whereas DNA contains thymine.
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. Correct. The greater electronegativity of oxygen and nitrogen compared with hydrogen makes for unequal sharing of electrons, which results in partial negative charges associated with the oxygen and nitrogen atoms and partial positive charges associated with the hydrogen atoms in both molecules. The attraction between opposite charges results in the formation of the hydrogen bond represented in the figure.
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. Correct. Carbohydrates occur in many forms. Glucose is an example of a monomer, sucrose is a chain of two carbohydrate monomers, and starch is an example of a carbohydrate with a branched structure.
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. Correct. Palmitic acid is a saturated fatty acid. The absence of carbon-carbon double bonds in palmitic acid allows the molecules to pack closely together and form a solid at room temperature.
Figure 1 is a diagram of water molecules at the air-water interface at the surface of a pond. Figure 1. Alignment of water molecules at air-water interface 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. Correct. Hydrogen bonds form between water molecules due to the partial charges produced as a result of the polarity of the water molecule. The strength of the attraction between the water molecules allows organisms to walk across the surface without breaking the hydrogen bonds.
Polypeptides are continuously being formed and degraded. One of these processes is shown. Figure 1. Polypeptide reaction 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. Correct. The reaction shows the polypeptide being split into two smaller units with the addition of a hydroxide ion and a hydrogen ion from water. This facilitates the breaking of the bond holding the polypeptide together.
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 CFTRCFTR protein. B. It will affect the primary structure of the CFTRCFTR protein, but the other levels of protein structure will not be affected. C. It will affect the secondary and tertiary structures of the CFTRCFTR protein, but the primary structure will not be affected. D. It will affect the primary, secondary, and tertiary structures of the CFTRCFTR protein.
D. It will affect the primary, secondary, and tertiary structures of the CFTRCFTR protein. Correct. A change in the primary structure of the CFTRCFTR protein will lead to changes in the secondary and tertiary structures. As a result, the protein will not fold properly and will not function normally.
Which of the following conclusions is most clearly supported by the representations of nucleic acid #1 and nucleic acid #2 ? A. Nucleic acid #1#1 contains only purines, whereas nucleic acid #2#2 contains only pyrimidines. B. Nucleic acid #1#1 contains the sugar ribose, whereas nucleic acid #2#2 contains the sugar deoxyribose. C. Nucleic acid #1#1 contains positively charged phosphate groups, whereas nucleic acid #2#2 does not. D. Nucleic acid #1#1 contains adenine-thymine base pairs, whereas nucleic acid #2#2 does not.
D. Nucleic acid #1#1 contains adenine-thymine base pairs, whereas nucleic acid #2#2 does not Correct. The representation of nucleic acid #1#1 shows adenine-thymine base pairs, whereas the representation of nucleic acid #2#2 shows only uracil in the nucleotide chain and does not show any base pairing.
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. Correct. As shown in the figure, the ammonia molecules released by the fish are converted by the bacteria to nitrites and nitrates. The plants absorb the nitrates, which are nitrogen-containing nutrients that the plants use to make the amino acids and nucleotides needed for building proteins and nucleic acids.
Figure 1 represents a common process that occurs in organisms. Figure 1. Structural formula for a common biological reaction 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 Correct. This reaction combines two smaller amino acids to form a dipeptide (a step in the formation of a protein) with the release of water. The presence of nitrogen is consistent with both amino acids and proteins. The combining of smaller molecules to form a larger molecule with the release of water is a dehydration synthesis reaction.
