Unit 1: The Chemistry of Life
Which of the following best describes the formation of the bond shown in Figure 1?
A covalent bond is formed between a carbon atom and a nitrogen atom along with the formation of 𝐻2𝑂
Which of the following statements best describes how organisms such as rabbits obtain the carbon necessary for building biological molecules?
Rabbits eat plants and break down plant molecules to obtain carbon and other atoms that they rearrange into new carbon-containing molecules
Humans produce sweat as a cooling mechanism to maintain a stable internal temperature. Which of the following best explains how the properties of water contribute to this physiological process?
The high heat of vaporization of water allows the body to remove excess heat through a phase change of water from liquid to gas
Which of the following best describes the structures of carbohydrates?
They occur as monomers, chains of monomers, and branched structures
If 30% of the nucleotides in a single-stranded RNA molecule are adenine, then what percent are expected to be thymine?
0%
Which of the following best explains how higher concentrations of nitrogen and phosphorous contribute to eutrophication?
Algae require nitrogen and phosphorous to build macromolecules, so higher concentrations of these nutrients can result in algal blooms.
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?
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 bond
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?
DNA
A researcher measured the temperature at which two different samples of double-stranded DNA denature (separate into single strands). Sample 1 denatured at a significantly lower temperature than sample 2 did. Based on the data, the researcher claims that the DNA in sample 2 is composed of a higher percentage of guanine and cytosine than the DNA in sample 1 is. Which of the following best supports the researcher's claim?
Guanine-cytosine pairs denature at a higher temperature because they have more hydrogen bonds between them than adenine-thymine pairs do
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?
Having two oppositely oriented layers of phospholipids allows only the hydrophilic heads to interact with water inside and outside of the cell.
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?
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
Which of the following is responsible for the cohesive property of water?
Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule
Which of the following is most directly responsible for water's unique properties?
It forms hydrogen bonds
Which of the following best explains how the extensive folding of the inner mitochondrial membrane benefits a eukaryotic cell
It increases the area available for proteins involved in energy transfer.
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?
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?
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?
Nucleic acid #1 contains adenine-thymine base pairs, whereas nucleic acid #2 does not
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?
Palmitic acid, because the absence of carbon-carbon double bonds allows the molecules to pack closely together
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 ofthe following statements best describes how molecules released by the fish become nutrients for the plants?
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
DNA and RNA are nucleic acids that can store biological information based on the sequence of their nucleotide monomers. The figure above 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?
The backbone of DNA contains deoxyribose, whereas the backbone of RNA contains ribose
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?
The carbohydrates have different properties because they have different arrangements of carbon, hydrogen and oxygen atom
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−𝑆𝑏𝑜𝑛𝑑𝑠. The structure of cysteine is shown to the right. Which of the following best describes the effect of a greater number of cysteine amino acids on the stability of the proteins?
The change leads to increased protein stability because of an increased number of S-S bonds in the tertiary structure of the protein
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 phosphorous and chlorophyll a concentration (Figure 2). Which of the following was the dependent variable in the researcher's study?
The concentration of chlorophyll a
Which of the following describes the relationship between the amount of chlorophyll a in a water sample and the concentration of nitrogen in that sample?
The concentrations of nitrogen and chlorophyll a are directly correlated
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.The observed difference between the groups most likely resulted from the ability of the seedlings to produce which of the following monomers?
The diagram showing an amino acid and a nucleic acid
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 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 ofthe 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 with the hydrophobic amino acids hiding in the middle of the protein surrounded by the hydrophilic amino acids
Figure 1 represents a common process that occurs in organisms.Which of the following is an accurate description of the process shown in Figure 1?
The formation of a covalent peptide bond in a dehydration synthesis reaction.
The figure below represents a nucleic acid fragment that is made up of four nucleotides linked together in a chain. Which of the following characteristics of the figure best shows that the fragment is RNA and not DNA?
The identity of each nitrogenous bas
Which of the following best describes how amino acids affect the tertiary structure of a protein?
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
The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge
Two groups of students attempted to re-create the primitive atmospheric conditions of early Earth using the apparatus represented below. Each group ran the experiment with different gas mixtures in the apparatus. Which of the following statements best justifies the claim that the conditions in at least one of the experiments could generate the molecular building blocks essential for life?
The nitrogen 𝑁2gas and ammonia 𝑁𝐻3gas in experiment 1 could provide the elemental nitrogen required for the formation of amino acids
Ultraviolet (UV) radiation can damage DNA by breaking weak bonds. Which of the following best explains how this occurs?
UV radiation disrupts the double helix structure by breaking the hydrogen bonds between the nitrogenous base pairs
The synthesis of protein or carbohydrate polymers always produces which ofthe following as a byproduct?
Water
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?
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.
