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AEPA Biology (NT305) study materials
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AEPA Biology (NT305) practice questions

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Question 1Scientific Inquiry and the Nature of Science

A student wants to determine whether fertilizer concentration affects the growth rate of bean plants. Which statement best describes the independent variable in this experiment?

  1. The concentration of fertilizer applied to the plants Correct answer.
  2. The average height of the plants at the end of the study
  3. The amount of water each plant receives
  4. The type of soil used in the pots

Explanation

The independent variable is the factor the experimenter deliberately manipulates, which here is fertilizer concentration. All other conditions, such as water and soil, are held constant as controlled variables. The measured outcome, plant height, is the dependent variable.

Question 2Scientific Inquiry and the Nature of Science

A researcher measures the mass of the same sample five times and obtains nearly identical values. Which aspect of the data does this most directly support?

  1. Validity of the experimental design
  2. Generalizability of the findings
  3. Statistical significance of the results
  4. Precision of the measurements Correct answer.

Explanation

Precision refers to how closely repeated measurements agree with one another. Consistently similar values indicate high precision regardless of whether the values are accurate. Accuracy and validity involve comparison to a true value or sound design, which repeated agreement alone cannot establish.

Question 3Scientific Inquiry and the Nature of Science

In a controlled experiment, a scientist includes a group that receives no treatment. What is the primary purpose of this group?

  1. To eliminate the need for repeated trials
  2. To increase the total sample size for statistical power
  3. To ensure that the dependent variable stays constant
  4. To provide a baseline for comparison with treated groups Correct answer.

Explanation

A control group establishes a baseline against which the effects of the treatment can be judged. Without it, observed changes cannot be confidently attributed to the independent variable. Control groups do not remove the need for replication or fix the dependent variable.

Question 4Scientific Inquiry and the Nature of Science

Which of the following is the best example of a testable scientific hypothesis?

  1. Photosynthesis is the most important process on Earth.
  2. Bean plants are the most beautiful plants to grow.
  3. Increasing light exposure increases the rate of photosynthesis in aquatic plants. Correct answer.
  4. Plants probably prefer classical music over silence.

Explanation

A testable hypothesis predicts a measurable relationship between variables that can be supported or refuted by observation. The light-and-photosynthesis statement predicts a measurable effect that can be tested. Statements about beauty or importance are value judgments that cannot be tested empirically.

Question 5Scientific Inquiry and the Nature of Science

A scientist reports that a new drug reduced symptoms in 60% of patients compared with 40% in a placebo group. Before accepting the conclusion, a reviewer should be most concerned with which feature of the study?

  1. The publication date of the study
  2. Whether the difference is statistically significant and the sample adequate Correct answer.
  3. The brand name of the drug tested
  4. The color of the pills given to each group

Explanation

A numerical difference between groups must be evaluated for statistical significance and adequate sample size before it can be attributed to the treatment. Without such analysis, the difference could reflect random variation. Cosmetic or bibliographic details are not central to the inference.

Question 6Scientific Inquiry and the Nature of Science

A student graphs data showing that as temperature increases from 10°C to 35°C, enzyme activity rises and then sharply falls. Which conclusion is best supported by this pattern?

  1. Enzyme activity is unaffected by temperature.
  2. Enzyme activity has an optimal temperature range. Correct answer.
  3. Enzyme activity decreases continuously with temperature.
  4. Enzyme activity increases continuously with temperature.

Explanation

A rise followed by a sharp decline indicates a peak, meaning the enzyme functions best within a particular temperature range. Beyond that range, denaturation or other effects reduce activity. Continuous increase or decrease would show a monotonic trend, which the data contradict.

Question 7Scientific Inquiry and the Nature of Science

Which practice most strengthens the reliability of experimental findings?

  1. Repeating the experiment multiple times and averaging results Correct answer.
  2. Using a single large trial without replication
  3. Changing the procedure between trials
  4. Reporting only the trials that support the hypothesis

Explanation

Replication reduces the influence of random variation and increases confidence that results are consistent. Averaging across repeated trials produces a more reliable estimate. Selectively reporting or altering procedures undermines reliability.

Question 8Scientific Inquiry and the Nature of Science

A scientist's results contradict an established model. According to the nature of science, what is the most appropriate response?

  1. Ignore the results to avoid confusion in the field
  2. Immediately discard the entire model regardless of verification
  3. Reject the results because the model is well established
  4. Repeat and verify the findings, then consider revising the model if evidence holds Correct answer.

Explanation

Scientific knowledge is open to revision when evidence warrants it, but new results require verification before overturning established ideas. Replication and scrutiny determine whether the contradiction is genuine. Neither automatic rejection nor immediate abandonment reflects sound scientific practice.

Question 9Scientific Inquiry and the Nature of Science

A student claims that a hypothesis is proven true after one experiment supports it. Which statement best corrects this misconception?

  1. Hypotheses become laws after a single confirming experiment
  2. Supporting evidence strengthens a hypothesis but does not prove it absolutely Correct answer.
  3. A hypothesis is proven once it is published in a journal
  4. Hypotheses can never be tested by experiments

Explanation

In science, hypotheses are supported or refuted by evidence but are not proven with absolute certainty, since future evidence could conflict. Scientific conclusions are always provisional. Publication or a single experiment does not confer proof.

Question 10Scientific Inquiry and the Nature of Science

A researcher wants to test how pH affects enzyme activity while keeping temperature and substrate concentration constant. Why is holding these other factors constant important?

  1. It guarantees the results will be statistically significant
  2. It prevents the dependent variable from being measured
  3. It ensures any observed change is due to pH rather than other factors Correct answer.
  4. It eliminates the need for a control group

Explanation

Controlling other variables prevents confounding, so changes in the dependent variable can be attributed to the manipulated factor. This isolation of variables is central to experimental validity. It does not guarantee significance or replace a control group.

Question 11Scientific Inquiry and the Nature of Science

A data table shows a sample mean of 12.4 with a standard deviation of 0.3 for group A and a mean of 12.6 with a standard deviation of 4.1 for group B. Which interpretation is most reasonable?

  1. Group B's measurements are more consistent than group A's
  2. Both groups have identical variability
  3. Group A's measurements are more consistent than group B's Correct answer.
  4. Standard deviation cannot be compared between groups

Explanation

Standard deviation measures the spread of data around the mean; a smaller value indicates greater consistency. Group A's much smaller standard deviation shows its measurements cluster more tightly. The means are similar, but the variability differs markedly.

Question 12Scientific Inquiry and the Nature of Science

Which of the following best describes the role of peer review in scientific communication?

  1. It guarantees that published results are correct
  2. It determines which hypotheses are most popular
  3. It subjects findings to scrutiny by qualified experts before publication Correct answer.
  4. It replaces the need for experimental replication

Explanation

Peer review provides independent evaluation by experts who assess methodology, evidence, and interpretation before publication. It improves quality but does not guarantee correctness or replace replication. It is not a popularity contest.

Question 13Scientific Inquiry and the Nature of Science

A scientist uses a model to predict how a population will change over time. Which statement best describes a limitation of scientific models?

  1. Models simplify reality and may omit factors that affect outcomes Correct answer.
  2. Models are always exact copies of reality
  3. Models eliminate all uncertainty from conclusions
  4. Models cannot be used to make predictions

Explanation

Models necessarily simplify complex systems, so they may leave out variables that influence real outcomes. This simplification is useful but introduces limitations and uncertainty. Models are not exact copies and are specifically built to make predictions.

Question 14Scientific Inquiry and the Nature of Science

A graph plots plant growth against light intensity and shows a curve that rises steeply and then levels off. What does the leveling-off portion most likely indicate?

  1. Light intensity no longer limits growth at high levels Correct answer.
  2. The data are invalid because the curve is not straight
  3. Growth is independent of light at low intensities
  4. Plant growth decreases as light increases

Explanation

A plateau indicates that some other factor becomes limiting once light is abundant, so additional light no longer increases growth. This reflects a limiting-factor relationship. A straight line is not required for valid data.

Question 15Scientific Inquiry and the Nature of Science

A scientist measures the length of a beetle as 3.2 cm using a ruler marked in millimeters. Another scientist measures the same beetle as 3.4 cm. This discrepancy most likely reflects a problem with which aspect of measurement?

  1. The independent variable
  2. Precision only
  3. Accuracy and measurement technique Correct answer.
  4. The hypothesis being tested

Explanation

A ruler marked in millimeters should allow readings to within about 0.1 cm, so a 0.2 cm difference suggests inaccuracy or inconsistent technique rather than random precision limits. Accuracy concerns closeness to the true value. Hypothesis and independent variable are conceptual, not measurement issues.

Question 16Scientific Inquiry and the Nature of Science

Which statement best explains why scientists use the metric system and standardized units in reporting data?

  1. It removes the need for statistical analysis
  2. It makes all measurements perfectly accurate
  3. It makes results easier to compare and reproduce across studies Correct answer.
  4. It guarantees that experiments will succeed

Explanation

Standardized units allow researchers worldwide to interpret, compare, and reproduce one another's results. This supports communication and verification in science. Standardization does not ensure success, accuracy, or replace statistics.

Question 17Scientific Inquiry and the Nature of Science

A student reads that a correlation exists between ice cream sales and drowning incidents. What is the most scientifically sound interpretation?

  1. Both variables may be influenced by a third factor such as warm weather Correct answer.
  2. Drowning causes increased ice cream sales
  3. The correlation proves a causal relationship
  4. Eating ice cream causes drowning

Explanation

Correlation does not establish causation; both variables can be driven by a common factor such as seasonal warmth. A plausible confounding variable explains the association. Causal claims require controlled evidence, not correlation alone.

Question 18Scientific Inquiry and the Nature of Science

A scientist designs an experiment to test a hypothesis and obtains results that do not support it. What is the most appropriate next step in the scientific process?

  1. Alter the data so they support the hypothesis
  2. Report the results as if they supported the hypothesis
  3. Revise the hypothesis or design a new experiment based on the findings Correct answer.
  4. Abandon the field of study entirely

Explanation

Unexpected results are valuable and should prompt revision of the hypothesis or refinement of the experimental design. Science advances through testing and revising ideas. Misrepresenting or altering data is scientific misconduct.

Question 19Scientific Inquiry and the Nature of Science

In a study, participants are randomly assigned to treatment and control groups. What is the main benefit of random assignment?

  1. It reduces bias by distributing unknown variables evenly across groups Correct answer.
  2. It ensures the treatment is effective
  3. It eliminates the need for a control group
  4. It guarantees the sample represents the whole population

Explanation

Random assignment helps distribute both known and unknown confounding variables evenly among groups, reducing systematic bias. It does not guarantee effectiveness or representativeness. A control group remains essential.

Question 20Scientific Inquiry and the Nature of Science

A study finds that a new fertilizer increases crop yield by 5% with a p-value of 0.04. Which interpretation is most appropriate?

  1. The fertilizer has no effect on yield
  2. The p-value proves the fertilizer will work on every farm
  3. The result is statistically significant at the conventional 0.05 level Correct answer.
  4. The 5% increase is definitely caused by chance

Explanation

A p-value of 0.04 is below the conventional 0.05 threshold, indicating the observed difference is unlikely to be due to chance alone. This supports statistical significance but does not guarantee universal applicability. It does not prove the effect is due to chance or that there is no effect.

Question 21Scientific Inquiry and the Nature of Science

A researcher studying bird migration tags 40 birds and tracks them for one season. Which factor most limits the ability to generalize the findings to all birds of that species?

  1. The small sample size and single-season duration Correct answer.
  2. The use of tags to identify individual birds
  3. The decision to record migration dates
  4. The choice to study a migratory species

Explanation

Generalizability depends on sample size and how representative the sample and time period are. A small sample over one season may not capture variation across years or populations. Tagging and recording dates are standard methods, not limitations.

Question 22Scientific Inquiry and the Nature of Science

Two scientists interpret the same data set differently. According to the nature of science, what best explains this situation?

  1. Data interpretation involves assumptions and reasoning that can legitimately differ Correct answer.
  2. One scientist must be committing fraud
  3. Scientific data are always ambiguous and meaningless
  4. Only one interpretation can ever be valid, and it is determined by majority vote

Explanation

Interpretation of data draws on assumptions, models, and reasoning that can lead competent scientists to different conclusions. Such disagreement is resolved through further evidence and scrutiny, not by assuming misconduct. Data are not meaningless simply because interpretations differ.

Question 23Scientific Inquiry and the Nature of Science

A scientist wants to determine whether a treatment causes a change, but cannot randomly assign subjects for ethical reasons. Which approach best strengthens a causal inference from observational data?

  1. Controlling for confounding variables through statistical methods and matching Correct answer.
  2. Reporting results without any comparison group
  3. Collecting more subjective opinions about the treatment
  4. Removing all data that do not fit the expected pattern

Explanation

When randomization is impossible, statistical control and matching on confounding variables help approximate a fair comparison. This reduces alternative explanations for observed effects. Subjective opinions, data removal, and lack of comparison weaken inference.

Question 24Scientific Inquiry and the Nature of Science

A textbook presents a scientific theory. Which statement best reflects the scientific meaning of 'theory'?

  1. A guess that has not been tested
  2. A well-substantiated explanation supported by extensive evidence Correct answer.
  3. A hypothesis that failed testing
  4. A temporary opinion held by a single scientist

Explanation

In science, a theory is a well-supported explanatory framework built from extensive evidence and repeated testing. It is far stronger than a guess or opinion. A failed hypothesis is discarded, not elevated to theory.

Question 25Scientific Inquiry and the Nature of Science

A student records temperature readings of 20°C, 20°C, 20°C, and 20°C using a thermometer that is consistently 2°C too high. Which statement best describes these measurements?

  1. They are precise but not accurate Correct answer.
  2. They are neither precise nor accurate
  3. They are both accurate and precise
  4. They are accurate but not precise

Explanation

The readings agree closely with each other, indicating high precision, but the consistent 2°C offset means they deviate from the true value, indicating low accuracy. Precision and accuracy are independent qualities. Systematic error affects accuracy, not necessarily precision.

Question 26Scientific Inquiry and the Nature of Science

In a controlled experiment, which variable is deliberately changed by the researcher?

  1. Control variable
  2. Independent variable Correct answer.
  3. Dependent variable
  4. Confounding variable

Explanation

The independent variable is the factor that the experimenter manipulates to observe its effect. The dependent variable is the response that is measured, while control variables are kept constant to prevent confounding.

Question 27Scientific Inquiry and the Nature of Science

A student wants to determine the effect of light intensity on the rate of photosynthesis in Elodea. Which is the most appropriate dependent variable?

  1. The wattage of the light bulb used
  2. The distance of the light source from the plant
  3. The temperature of the water bath
  4. The number of oxygen bubbles produced per minute Correct answer.

Explanation

The dependent variable is the response that is measured, which in this case is the rate of photosynthesis, often estimated by counting oxygen bubbles. The other options are either the independent variable or controlled variables.

Question 28Scientific Inquiry and the Nature of Science

Which of the following best describes a scientific hypothesis?

  1. A proven fact that cannot be challenged
  2. A final conclusion drawn from an experiment
  3. A broad explanation supported by extensive evidence
  4. A testable explanation for an observation Correct answer.

Explanation

A hypothesis is a proposed, testable explanation for a phenomenon that can be supported or refuted by experimentation. It is not a proven fact, a conclusion, or a broad theory.

Question 29Scientific Inquiry and the Nature of Science

A scientist measures the mass of a sample three times and obtains 12.1 g, 12.2 g, and 12.1 g. The true mass is 15.0 g. Which statement best describes the measurements?

  1. They are both accurate and precise
  2. They are neither accurate nor precise
  3. They are accurate but not precise
  4. They are precise but not accurate Correct answer.

Explanation

Precision refers to how close repeated measurements are to each other, while accuracy refers to how close a measurement is to the true value. Here the measurements are close together (precise) but far from the true value (not accurate).

Question 30Scientific Inquiry and the Nature of Science

A scientist conducts an experiment and finds that a new drug significantly reduces blood pressure compared to a placebo. However, the study only included 10 participants. What is the most appropriate conclusion?

  1. The drug is proven effective and should be prescribed immediately
  2. The experiment should be discarded because the sample is too small
  3. The results are promising but need replication with a larger sample Correct answer.
  4. The results are invalid because the sample size was not random

Explanation

A small sample size increases the risk that the results are due to chance, so the findings are preliminary and require replication with a larger, more representative sample before strong conclusions can be drawn. The other options are either premature or overly dismissive.

Question 31Scientific Inquiry and the Nature of Science

Which of the following is the best example of a scientific model?

  1. A hypothesis that plants grow faster with fertilizer
  2. A law that states energy is conserved
  3. A theory that explains the origin of the universe
  4. A computer simulation predicting hurricane paths Correct answer.

Explanation

A scientific model is a simplified representation of a system used to make predictions or explain phenomena; a computer simulation is a common type of model. Laws, hypotheses, and theories are different kinds of scientific knowledge.

Question 32Scientific Inquiry and the Nature of Science

In an experiment, the control group is used to

  1. test the hypothesis directly
  2. provide a baseline for comparison Correct answer.
  3. eliminate all variables
  4. increase the sample size

Explanation

The control group serves as a standard against which the experimental group is compared, helping to isolate the effect of the independent variable. It does not test the hypothesis directly nor eliminate all variables.

Question 33Scientific Inquiry and the Nature of Science

A scientist wants to test the effect of a new fertilizer on plant growth. She plants 20 seeds in each of two groups: one group receives fertilizer, the other does not. All other conditions are kept identical. What is the independent variable?

  1. The type of soil used
  2. The amount of water given
  3. The presence or absence of fertilizer Correct answer.
  4. The height of the plants after four weeks

Explanation

The independent variable is the factor that is deliberately manipulated, which is whether fertilizer is applied. Plant height is the dependent variable, and soil type and water are controlled variables.

Question 34Scientific Inquiry and the Nature of Science

A student claims that because a hypothesis is supported by one experiment, it is now a scientific theory. Which statement best explains why this claim is incorrect?

  1. A hypothesis can never become a theory
  2. A theory is a broad explanation supported by many lines of evidence, not a single experiment Correct answer.
  3. A theory is a guess, while a hypothesis is a proven fact
  4. A theory is only valid if it cannot be tested

Explanation

In science, a theory is a well-substantiated explanation of some aspect of the natural world that is supported by a large body of evidence. A single experiment can support a hypothesis but is not sufficient to establish a theory.

Question 35Scientific Inquiry and the Nature of Science

A scientist uses a model to predict the spread of an invasive species. Which statement best describes a limitation of this model?

  1. The model simplifies complex ecological interactions and may not account for all variables Correct answer.
  2. Models are only useful if they are perfect representations of reality
  3. The model is limited because it cannot be tested
  4. The model is based on mathematical equations and therefore cannot be accurate

Explanation

Models are simplifications of reality and therefore may omit factors that could affect the outcome. This simplification is a limitation but also a necessary feature of modeling.

Question 36Scientific Inquiry and the Nature of Science

A student notices that a plant placed near a window grows toward the light. Which of the following would be the most appropriate first step in a scientific investigation of this observation?

  1. Conclude that plants always grow toward light
  2. Research the effect of light on plant growth in scientific literature
  3. Design an experiment with multiple variables
  4. Formulate a testable hypothesis about light direction and plant growth Correct answer.

Explanation

The scientific process typically begins with observations that lead to questions and then to testable hypotheses. While literature research is valuable, formulating a hypothesis is a direct first step after making an observation.

Question 37Scientific Inquiry and the Nature of Science

Which of the following best describes the role of a control group in an experiment?

  1. It allows the researcher to test multiple hypotheses simultaneously
  2. It ensures that all variables are kept constant
  3. It provides a standard for comparison to isolate the effect of the independent variable Correct answer.
  4. It increases the reliability of the results by increasing sample size

Explanation

The control group is essential for comparison; it is treated identically to the experimental group except for the independent variable, allowing researchers to attribute differences to that variable.

Question 38Scientific Inquiry and the Nature of Science

A scientist performs an experiment and obtains a p-value of 0.03. Which interpretation is most appropriate?

  1. There is a 97% probability that the alternative hypothesis is true
  2. The results are not statistically significant at the 0.05 level
  3. There is a 3% probability that the null hypothesis is true
  4. There is a 3% probability of obtaining results at least as extreme as those observed if the null hypothesis is true Correct answer.

Explanation

A p-value indicates the probability of observing data as extreme as, or more extreme than, the actual data, assuming the null hypothesis is true. It is not the probability that the null hypothesis is true or that the alternative is true.

Question 39Scientific Inquiry and the Nature of Science

A researcher wants to determine whether a new teaching method improves test scores. She randomly assigns students to either the new method or the traditional method. Which of the following is the most important reason for random assignment?

  1. To ensure that the results can be generalized to all students
  2. To minimize preexisting differences between groups Correct answer.
  3. To increase the statistical power of the study
  4. To control the independent variable

Explanation

Random assignment helps ensure that the groups are comparable at the start of the experiment by distributing confounding variables evenly, reducing bias. It does not guarantee generalizability or directly control the independent variable.

Question 40Scientific Inquiry and the Nature of Science

A scientist is studying the effect of temperature on the rate of a chemical reaction. She measures the rate at five temperatures: 10°C, 20°C, 30°C, 40°C, and 50°C. Which type of graph is most appropriate for displaying these data?

  1. A bar graph with temperature on the x-axis and reaction rate on the y-axis
  2. A line graph with temperature on the x-axis and reaction rate on the y-axis Correct answer.
  3. A pie chart showing the proportion of reaction at each temperature
  4. A scatter plot with reaction rate on the x-axis and temperature on the y-axis

Explanation

A line graph is best for showing how a continuous variable (reaction rate) changes in response to another continuous variable (temperature). Bar graphs are better for categorical data, pie charts show parts of a whole, and a scatter plot is used to show the relationship between two variables but typically without connecting points.

Question 41Cell Biology and Biochemistry

Which organelle is the primary site of ATP production in a eukaryotic cell?

  1. Mitochondrion Correct answer.
  2. Lysosome
  3. Ribosome
  4. Golgi apparatus

Explanation

Oxidative phosphorylation takes place on the inner mitochondrial membrane, where the electron transport chain builds the proton gradient that drives ATP synthase. Other organelles listed perform sorting, digestion, or protein synthesis rather than bulk ATP generation.

Question 42Cell Biology and Biochemistry

A polypeptide is synthesized on a free ribosome in the cytosol. Where will this protein most likely function?

  1. In the endoplasmic reticulum lumen
  2. In the lysosomal lumen
  3. In the cytosol Correct answer.
  4. Outside the plasma membrane

Explanation

Proteins translated on free ribosomes lack a signal peptide that would direct them into the secretory pathway, so they typically fold and function in the cytosol. Proteins destined for the lumen of the ER, lysosomes, or secretion are made on rough ER ribosomes.

Question 43Cell Biology and Biochemistry

Which molecule serves as the immediate energy currency that directly powers most cellular work?

  1. ATP Correct answer.
  2. Pyruvate
  3. Glucose
  4. NADH

Explanation

ATP hydrolysis releases free energy that is coupled directly to endergonic reactions such as transport and biosynthesis. Glucose, NADH, and pyruvate are energy-rich but must be oxidized or processed first to regenerate ATP.

Question 44Cell Biology and Biochemistry

In the fluid mosaic model, which feature best describes the plasma membrane?

  1. A single layer of phospholipids surrounding the cytosol
  2. A solid sheet of cholesterol with no lateral movement
  3. A rigid lattice of protein and cellulose
  4. A phospholipid bilayer with embedded and peripheral proteins Correct answer.

Explanation

The fluid mosaic model describes a phospholipid bilayer in which proteins are embedded or associated and lipids and proteins can move laterally. This arrangement gives the membrane both fluidity and selective permeability.

Question 45Cell Biology and Biochemistry

Which transport process moves water across a membrane from lower to higher solute concentration without direct ATP expenditure?

  1. Osmosis Correct answer.
  2. Phagocytosis
  3. Facilitated diffusion of ions
  4. Active transport

Explanation

Osmosis is the passive movement of water through a selectively permeable membrane toward the region of higher solute concentration. It is driven by the water potential gradient and requires no direct ATP input.

Question 46Cell Biology and Biochemistry

A red blood cell is placed in a hypertonic solution. What is the most likely result?

  1. The cell swells and bursts
  2. The cell maintains its volume unchanged
  3. The cell shrinks as water leaves Correct answer.
  4. The cell actively pumps water inward

Explanation

In a hypertonic solution the external solute concentration is higher than inside the cell, so water moves out by osmosis and the cell shrinks. Cells cannot actively pump water to counteract this.

Question 47Cell Biology and Biochemistry

Which enzyme catalyzes the rate-limiting step of glycolysis?

  1. Pyruvate kinase
  2. Hexokinase
  3. Phosphofructokinase-1 Correct answer.
  4. Aldolase

Explanation

Phosphofructokinase-1 catalyzes the committed, rate-limiting step of glycolysis and is regulated by cellular energy charge. Hexokinase, aldolase, and pyruvate kinase act at other steps of the pathway.

Question 48Cell Biology and Biochemistry

During aerobic respiration, where does the citric acid cycle take place in a eukaryotic cell?

  1. Nucleus
  2. Cytosol
  3. Inner mitochondrial membrane
  4. Mitochondrial matrix Correct answer.

Explanation

The enzymes of the citric acid cycle, except succinate dehydrogenase, are soluble in the mitochondrial matrix. The inner membrane hosts the electron transport chain, while glycolysis occurs in the cytosol.

Question 49Cell Biology and Biochemistry

What is the primary role of oxygen in oxidative phosphorylation?

  1. It phosphorylates ADP directly
  2. It accepts electrons at the end of the electron transport chain Correct answer.
  3. It transports pyruvate into the matrix
  4. It donates electrons to complex I

Explanation

Oxygen is the terminal electron acceptor at complex IV, where it is reduced to water. This keeps electrons flowing through the chain so the proton gradient and ATP synthesis can continue.

Question 50Cell Biology and Biochemistry

A mutation eliminates the proton gradient across the inner mitochondrial membrane. Which outcome is most direct?

  1. ATP synthesis by ATP synthase stops Correct answer.
  2. Fatty acid oxidation ceases immediately
  3. Glycolysis can no longer produce ATP
  4. The citric acid cycle cannot oxidize acetyl-CoA

Explanation

ATP synthase relies on the proton-motive force to drive ADP phosphorylation, so loss of the gradient halts ATP synthesis. Glycolysis, the citric acid cycle, and fatty acid oxidation are not directly driven by the gradient itself.