AP Classroom Biology Unit 3

Based on Table 1, which of the following best explains the difference in water potential between certain solutions and the grapes?

Grape soda and NaCl have a lower water potential because these two solutions caused the grape to lose water.

Which of the following best describes the role of water in photosynthesis?

Water molecules donate electrons to the electron transport chain.

Tarui disease is an inherited disorder that is caused by mutations in PFKM, the gene that encodes a subunit of phosphofructokinase, an enzyme in the glycolysis pathway. Individuals with Tarui disease produce little or no functional phosphofructokinase in skeletal muscle cells. Based on Figure 1, which of the following best explains why a low carbohydrate diet is recommended for those with Tarui disease?

Carbohydrate metabolism requires all the reactions of glycolysis, and amino acids and fatty acids do not.

An increase in the concentration of protons in the cytosol will most likely have which of the following effects on glycolysis?

Glycolytic enzymes will denature as a result of the increased H+concentration.

A researcher claims that the synthesis of ATP from ADP and inorganic phosphate (Pi) is essential to cellular function.

ATP hydrolysis is an energy-releasing reaction that is often coupled with reactions that require an input of energy.

Which of the following claims is best supported by the experimental results?

Light is required for the electron transport chain to transfer electrons.

Alcohol dehydrogenase (ADH) is an enzyme that aids in the decomposition of ethyl alcohol (C2H5OH) into nontoxic substances. Methyl alcohol acts as a competitive inhibitor of ethyl alcohol by competing for the same active site on ADH. When attached to ADH, methyl alcohol is converted to formaldehyde, which is toxic in the body.

Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant?

Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

Which of the following actions will provide the most appropriate negative control for the experiment?

Repeating the experiment with denatured enzymes

On average, more ATP can be produced from an NADH molecule than can be produced from a molecule of FADH2. Based on Figure 1, which of the following best explains the difference in ATP production between these two molecules?

The electrons of FADH2 are transferred through three complexes of the electron transport chain whereas those of NADH are transferred through all four complexes.

The enzyme hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, which is an important step in glycolysis. The reaction involves the transfer of a phosphate group from ATP to glucose.

Either a glucose molecule or a water molecule can fit in the active site of hexokinase. The presence of a water molecule in hexokinase’s active site would result in the hydrolysis of ATP to ADP instead of the conversion of glucose to glucose-6-phosphate.

Which of the following statements best helps explain the reaction specificity of hexokinase?

Glucose has the right shape and charge to cause hexokinase to undergo a structural change needed for catalysis, whereas water does not.

A researcher claims that increased atmospheric carbon dioxide levels cause increased growth rates in plants.

Which of the following statements best supports the researcher’s claim?

Atmospheric carbon dioxide is the raw material for photosynthesis, which plants rely on for producing sugars and other organic compounds.

Which of the following best describes the data in Figure 1 ?

At a concentration above μ10 μM, drug X reduces melanoma cell survival.

A researcher has identified a compound that reverses the effect of drug X. Based on Figure 3, which of the following best explains how the compound acts in the pathway to reverse the effects of drug X?

c

A researcher designs an experiment to investigate the effect of environmental temperature on the function of an enzyme. For each trial included in the experiment, the researcher will add the enzyme and its substrate to an aqueous buffer solution and then measure the amount of product formed over 20 minutes.

Which of the following must remain the same for all trials of this experiment?

The initial concentration of the substrate

Which of the following statements best explains the processes of passive and active transport?

Passive transport is the net movement of substances down a concentration gradient that does not require metabolic energy. Active transport is the movement of substances up a concentration gradient that requires energy.

A researcher proposes a model of an enzyme-catalyzed reaction in which a reactant is converted to a product. The model is based on the idea that the reactant passes through a transition state within the enzyme-substrate complex before the reactant is converted to the product.

Which of the following statements best helps explain how the enzyme speeds up the reaction?

The enzyme’s active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction.

The fact that each line on the graph rises from left to right means that

larger fish consume more oxygen than smaller fish at all four temperatures

Trypsin and pepsin are enzymes that function in different areas of the digestive tract. One functions in the stomach, where the pH is between 1.5 and 3.5, while the other functions in the small intestines, where the pH is between 6 and 8.

Based on Figure 1, which of the following best describes where each enzyme functions?

Pepsin works in the stomach because the optimal pH for pepsin is acidic.

Which of the following outcomes will most likely result from the irreversible binding of GDP to the G protein?

The intracellular concentration of glycogen will increase.

Which of the following best explains the connection between energy, growth, and the maintenance of an ordered system in the experiment?

Energy input from light is required for the grass to grow and maintain an ordered structure.

Which of the following questions can best be answered by the diagram?

Does the addition of an enzyme reduce the activation energy required for a reaction?

Which of the following best describes the cellular location where pyruvate dehydrogenase is most likely active?

The mitochondrial matrix

The maximum production rate of acetyl-CoA under condition 1 is closest to which of the following?

1 micromole/sec

According to the results of this experiment, germination of tobacco seeds during the first week is

increased by exposure to light

Which of the following statements best justifies the inclusion of test tube V as a control in the experiment?

It will show the color change that occurs in the absence of enzyme activity.

Pyruvate kinase, a key enzyme in the glycolysis pathway, is inhibited by the amino acid alanine. The ability of alanine to inhibit the enzyme is not affected by increasing the concentration of substrate.

Which of the following best explains the mechanism by which alanine inhibits pyruvate kinase activity?

Alanine binds to an allosteric site of the enzyme, changing the shape of the enzyme’s active site.

Based on the data in Figure 1, which of the following most likely represents the change in energy that occurs when ATP hydrolysis is coupled with the phosphorylation of a substrate?

Line 1 represents ATP hydrolysis, and line 4 represents phosphorylation of a substrate.

Figure 1 shows the amount of product produced in an enzyme-catalyzed reaction over five minutes. Which of the following best explains how the rate of the reaction changes over time?

The rate decreases because the ratio of product to substrate increases.

Which of the following statements about the rate of CO2 fixation in the two types of plants is supported by the data shown in the figures?

At 21% O2, plant type 2 has a lower rate of CO2 fixation than plant type 1 does in both types of soil.

In addition to the pigments commonly associated with photosynthesis, a certain photosynthetic species contains two additional pigment types.

Which of the following best supports the claim that this species is better adapted to environmental changes than other photosynthetic species are?

The additional pigments allow the species containing them to harvest energy from wavelengths of light that the other photosynthetic species cannot use.

A researcher is investigating the effects of a chemical that makes thylakoid membranes permeable to hydrogen ions (H+). Which of the following is the most likely direct effect of adding the chemical to plant cells?

The chloroplasts will generate less ATP.

Which of the following statements best helps explain the reaction specificity of an enzyme?

The shape and charge of the substrates are compatible with the active site of the enzyme.

Newborn babies and hibernating animals contain a large amount of brown adipose (fat) tissue (BAT). Certain proteins in the BAT cells increase the permeability of the inner mitochondrial membrane to protons, disrupting the proton gradient.

Which of the following best predicts the effect of disrupting the proton gradient in BAT?

Electron transport and oxidative phosphorylation will be decoupled, generating more heat but less ATP.

The figures can best assist in answering which of the following questions?

Do electron transport chains create a gradient so that ATP synthase can generate ATP molecules?

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?

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

After a search of nucleotide sequence databases, researchers identified an IRE in the 5¢ untranslated region of a gene encoding aconitase, an enzyme involved in the Krebs cycle. Which of the following pieces of experimental evidence best supports the claim that the synthesis of aconitase is controlled by a mechanism similar to ferritin regulation?

The relative amount of aconitase protein increases in the presence of high levels of iron.