AP Bio - Practice Midterm

Which of the following describes the most likely location of cholesterol in an animal cell?

Embedded in the plasma membrane

The following questions refer to an experiment that is set up to determine the relative volume of O2 consumed by germinating and nongerminating (dry) pea seeds at two different temperatures. The change in volume is detected by using a respirometer over a given period of time. The data are given below. The rate of oxygen consumption in germinating pea seeds at 26ºC is Responses

0.05 mL / min

The figure above represents a rough endoplasmic reticulum. Which of the following best describes the role of the structure labeled Y?

Structure Y is the location where proteins are synthesized.

Which of the following best describes the hydrolysis of carbohydrates?

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

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?

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.

The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1 . Which of the following best describes how the amount of DNA in the cell changes during M phase?

The amount of DNA is halved as the cell divides into two daughter cells.

The following questions refer to the following diagram. For each phrase or sentence, select the labeled part to which it is most closely related. Each option may be used once, more than once, or not at all for each group. Site of conversion of chemical energy of glucose to ATP

A

The diagram above illustrates feedback control as exerted by the hormone thyroxine. Following surgical removal of the thyroid gland, the level of TSH in the blood will increase. Which of the following best explains this increase?

A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

Cancer can result from a variety of different mutational events. Which of the following is LEAST likely to result in the initiation of a cancerous tumor?

A defect in a cell-cycle checkpoint prevents a cell from entering the S phase.

A scientist determined the rate of an enzyme-catalyzed reaction by measuring the amount of product formed over time. The following curve was generated from the data collected. What is the most likely explanation for the change in the slope of the line between 3 and 5 minutes?

A large amount of the substrate had been consumed.

The graph above shows changes in glucagon and insulin secretions at different concentrations of blood glucose. Which of the following feedback mechanisms is best supported by the data?

A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released.

Figure 1 shows a model of how a channel protein influences the movement of a particle across a cell's plasma membrane. Figure 1. A section of a cell's plasma membrane, showing a channel protein and a concentration gradient across the membrane An investigator wants to understand whether a newly found membrane protein is involved in membrane transport of a certain particle. Which investigation will help determine whether the new membrane protein is a channel protein involved in membrane transport? Responses

Add more of the proteins to the plasma membrane and measure the rate of the particle movement.

*Long Paragraph* Based on the model of ferritin synthesis presented in Figure 2, which of the following describes the role of feedback on the control of intracellular iron levels?

An increase in iron levels activates synthesis of ferritin protein. Ferritin protein in turn binds iron, thereby decreasing both free iron levels and ferritin synthesis.

Which of the following best describes the numbered areas?

Areas 1 and 3 are polar, since the membrane molecules are aligned with water molecules.

The enzyme trypsin aids in protein digestion in the small intestine. The relative activity of trypsin at different pH values is shown in Figure 1. Which of the following statements best explains the activity levels of trypsin shown in Figure 1 ?

At extremely low pH values, trypsin is denatured and cannot function efficiently.

The following questions refer to the following diagram. For each phrase or sentence, select the labeled part to which it is most closely related. Each option may be used once, more than once, or not at all for each group. Site of glucose synthesis

B

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? Responses

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

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? Responses

DNA

Over 100 different types of G-protein-linked receptors have been observed in eukaryotes, including scent receptors in animals, mating-signal receptors in yeasts, and light-sensing proteins in vertebrates. The proton pumps of bacteria have protein structures similar to G-protein-linked receptors. Based on this information, which of the following scientific questions will best guide research on the evolution of G-protein-linked signal transduction?

Did the G-protein-linked signal transduction pathway in eukaryotes arise from a precursor in prokaryotes?

Which of the following claims is scientifically accurate and consistent with an observation that a decrease in lysosome production within a cell leads to a decline in mitochondrial activity?

Fewer lysosomes will be available to break down macromolecules to provide the necessary nutrients for cellular respiration.

Which of the following best describes the process by which gas from the atmosphere is obtained by plants and used to build lipids? Responses

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

A cell is treated with a drug that prevents the formation of new lysosomes. The cell continues to transcribe the genes that code for the hydrolytic enzymes that are normally found in lysosomes and continues to translate the mRNAs for those proteins on membrane-bound ribosomes. The hydrolytic enzymes are most likely to accumulate in which of the following cellular structures?

Golgi complex

Many human cells can be stimulated to divide by hormonelike growth factors that bind to receptor proteins (R) on the plasma membrane and trigger an internal signal-transduction cascade. In many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. Contact inhibition occurs when proteins called cell adhesion molecules (CAMs) interact, causing them to change shape so that the growth-factor signaling proteins that normally associate with CAMs are replaced by another protein, called M. Both pathways are depicted in the figures below. Which of the following statements accurately uses the information presented to support the hypothesis that interruption of M function in a single body cell can result in cancer?

Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells.

Which of the following is responsible for the cohesive property of water? Responses

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

The following questions refer to an experiment that is set up to determine the relative volume of O2 consumed by germinating and nongerminating (dry) pea seeds at two different temperatures. The change in volume is detected by using a respirometer over a given period of time. The data are given below. Which of the following conclusions is best supported by the data?

In pea seeds an increase in temperature results in an increase in oxygen consumption.

A model of the plasma membrane showing several biological molecules, including a transmembrane protein, is shown in Figure 1. Which statement best explains why correct protein folding is critical in the transmembrane protein shown above? Responses

Interactions of the hydrophobic and hydrophilic amino acids help to anchor the protein in the membrane.

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? Responses

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 function of which of the following organelles directly requires oxygen?

Mitochondrion

The manner in which several different ions and molecules move through a cell membrane is shown in the diagram above. For each ion or molecule, the relative concentration on each side of the membrane is indicated. Which of the following accurately describes one of the movements taking place? Responses

Na+ transport out of the cell requires ATP hydrolysis.

Figure 1. Activity levels of two digestive enzymes over a range of pH 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? Responses

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

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.

Which of the following can be used to determine the rate of enzyme-catalyzed reactions?

Rate of disappearance of the substrate

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 differences between the groups most likely resulted from differences in the ability of the seedlings to produce which of the following monomers?

Sawdust will not provide sufficient amounts of nitrogen and phosphorus, resulting in the seedlings having a reduced ability to produce both of the monomers shown (amino acids and nucleotides). (C)

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 atoms.

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.

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

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? Responses

The high heat of vaporization of water allows the body to remove excess heat through a phase change of water from liquid to gas.

The model below shows the structure of a portion of a plasma membrane in an animal cell. Which statement best explains the orientation of the phospholipid molecules in this model?

The hydrophilic phosphate groups of the phospholipid molecules are attracted to the aqueous internal and external environments.

Muscle cells have high ATP demands. Which of the following is a scientific claim about how the structure of the mitochondria in muscle cells should be different than it is in other cells because of the high energy demands of mitochondria?

The inner membrane of the mitochondria in muscle cells should have more folds to increase the surface area, allowing more ATP to be synthesized.

Figure 1. Change in the relative concentration of product over time 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? Responses

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

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.

A mutation in the upland cotton plant causes the development of chloroplasts with a single outer membrane and no internal membranes. Which of the following would most likely be observed in chloroplasts of cotton plants with this mutation? Responses

They would be unable to generate the ATP and NADPH needed to make sugars, because these processes occur on membranes within the chloroplast.

*Long Paragraph* Based on the model of ferritin synthesis presented in Figure 2, which of the following best describes the mechanism whereby iron most likely regulates ferritin production?

Translation occurs under high intracellular iron concentration when the IRP-iron complex dissociates from ferritin mRNA, permitting ribosomes access to the ferritin coding region.

The synthesis of protein or carbohydrate polymers always produces which of the following as a byproduct?

Water

Simple diffusion and facilitated diffusion are related in that both Responses A

depend on a concentration gradient

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students' results are shown in graph 1. If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be Responses

lower than the level at pH 9

A scientist determined the rate of an enzyme-catalyzed reaction by measuring the amount of product formed over time. The following curve was generated from the data collected. The rate of the reaction could also be determined by

measuring the change in the amount of substrate

The organelle that is a major producer of ATP and is found in both heterotrophs and autotrophs is the Responses

mitochondrion