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Praxis Biology 5236 study materials
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Praxis Biology 5236 practice questions

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Question 1Basic Principles of Science

In scientific inquiry, a hypothesis is best described as which of the following?

  1. a testable prediction about an expected outcome Correct answer.
  2. a broad explanation supported by extensive evidence
  3. a proven fact that cannot be challenged
  4. a summary of the data collected during an experiment

Explanation

A hypothesis is a testable, falsifiable prediction about how variables are related. It guides an experiment and is either supported or rejected by evidence. Broader, heavily supported explanations are theories, while data summaries are results.

Question 2Basic Principles of Science

A student tests how light intensity affects the rate of photosynthesis in pondweed. Which factor is the independent variable?

  1. temperature of the water
  2. rate of photosynthesis
  3. light intensity Correct answer.
  4. amount of pondweed

Explanation

The independent variable is the factor deliberately changed by the researcher. Light intensity is manipulated, while the photosynthesis rate is the measured dependent variable. The amount of pondweed and water temperature are held constant.

Question 3Basic Principles of Science

Why is a control group included in an experiment?

  1. to ensure that the hypothesis is correct
  2. to provide a baseline for comparison Correct answer.
  3. to eliminate the need for repeated measurements
  4. to increase the total number of trials

Explanation

A control group is not exposed to the treatment and provides a baseline against which the experimental group is compared. This helps isolate the effect of the independent variable. Controls do not guarantee a correct hypothesis.

Question 4Basic Principles of Science

Which SI-derived unit is used to express volume?

  1. newton
  2. gram
  3. kelvin
  4. cubic meter Correct answer.

Explanation

Volume is a derived quantity equal to length cubed, so its SI-derived unit is the cubic meter. The gram measures mass, the newton measures force, and the kelvin measures temperature.

Question 5Basic Principles of Science

The high specific heat of water is most directly important because it does which of the following?

  1. enables water to rise in narrow plant tubes
  2. allows water to dissolve many ionic compounds
  3. creates surface tension at the water surface
  4. helps organisms resist rapid temperature changes Correct answer.

Explanation

Specific heat is the amount of heat needed to change a substance's temperature. Because water has a high specific heat, it absorbs or releases large amounts of heat with little temperature change, buffering living systems. Dissolving, surface tension, and capillary rise depend on other properties.

Question 6Basic Principles of Science

A solution with a pH of 3 is best described as which of the following?

  1. neutral, with equal hydrogen and hydroxide ions
  2. basic, with fewer hydrogen ions than a pH 7 solution
  3. acidic, with more hydrogen ions than a pH 7 solution Correct answer.
  4. basic, because its pH is below 7

Explanation

The pH scale is logarithmic and runs from 0 to 14, with values below 7 acidic. A pH of 3 indicates a higher hydrogen ion concentration than a neutral pH of 7 solution. Basic solutions have pH values above 7.

Question 7Basic Principles of Science

The monomer units that make up proteins are which of the following?

  1. amino acids Correct answer.
  2. fatty acids
  3. nucleotides
  4. monosaccharides

Explanation

Proteins are polymers built from amino acid monomers joined by peptide bonds. Fatty acids are components of lipids, monosaccharides are carbohydrate monomers, and nucleotides are nucleic acid monomers.

Question 8Basic Principles of Science

A balance consistently reports the mass of a 10.0 g object as 10.5 g on repeated trials. These measurements are best described as which of the following?

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

Explanation

Precision refers to how close repeated measurements are to one another, while accuracy refers to how close they are to the true value. The readings cluster tightly together but are consistently off from 10.0 g, so they are precise but not accurate.

Question 9Basic Principles of Science

In an experiment testing the effect of fertilizer on plant growth, which factor should be held constant?

  1. final height of each plant
  2. volume of water given to each plant Correct answer.
  3. amount of fertilizer applied
  4. number of leaves on each plant at the end

Explanation

Controlled variables are kept the same across treatment groups so they do not confound the results. Water volume should be identical for all plants, while fertilizer amount is the independent variable and height and leaf number are dependent variables.

Question 10Basic Principles of Science

Increasing the sample size in an experiment generally does which of the following?

  1. guarantees that the hypothesis will be supported
  2. reduces the effect of random variation on results Correct answer.
  3. removes the need for a control group
  4. increases the number of independent variables

Explanation

A larger sample reduces the influence of random variation and usually makes results more reliable. It does not guarantee a particular outcome, replace a control group, or change the number of variables being tested.

Question 11Basic Principles of Science

A scientific theory differs from a scientific law in that a theory does which of the following?

  1. explains why a phenomenon occurs Correct answer.
  2. is a guess that has not yet been tested
  3. describes a consistent relationship without explaining it
  4. can never be modified or rejected

Explanation

A theory is a well-supported explanation for a natural phenomenon, whereas a law describes a consistent relationship under stated conditions. Theories are strengthened, revised, or rejected as evidence accumulates.

Question 12Basic Principles of Science

Two data sets have the same mean, but set A has a larger standard deviation than set B. This indicates that set A does which of the following?

  1. contains a larger sample size
  2. is more precise than set B
  3. has a higher median than set B
  4. has values more spread out around the mean Correct answer.

Explanation

Standard deviation measures the spread of values around the mean. A larger standard deviation means the data are more dispersed, even if the means are identical. It does not directly indicate precision, sample size, or median.

Question 13Basic Principles of Science

Which graph is most appropriate for showing how a plant's height changes over eight weeks?

  1. line graph Correct answer.
  2. histogram
  3. pie chart
  4. bar graph

Explanation

A line graph is best for displaying continuous change over time because it shows trends across an ordered sequence of measurements. Bar graphs compare categories, pie charts show parts of a whole, and histograms show frequency distributions.

Question 14Basic Principles of Science

A student records the values 4, 6, 6, 8, and 11. What is the mean of these values?

  1. 6.5
  2. 8
  3. 6
  4. 7 Correct answer.

Explanation

The mean is calculated by adding all values and dividing by the number of values. The sum is 4 + 6 + 6 + 8 + 11 = 35, and 35 divided by 5 equals 7.

Question 15Basic Principles of Science

Water rises in a narrow glass tube mainly because of which of the following?

  1. adhesion to glass plus cohesion among water molecules Correct answer.
  2. water molecules repel each other
  3. water molecules are nonpolar
  4. water has an unusually low heat of vaporization for a liquid

Explanation

Capillary action results from adhesion between water and the glass walls and cohesion between water molecules. These forces allow water to climb narrow tubes. Water is polar and has a high, not low, heat of vaporization.

Question 16Basic Principles of Science

Hydrogen bonds between water molecules form mainly because of which of the following?

  1. oxygen is more electronegative than hydrogen Correct answer.
  2. water molecules share electrons equally
  3. water molecules contain ionic bonds
  4. hydrogen atoms carry a full negative charge

Explanation

Oxygen is more electronegative than hydrogen, so the shared electrons in each O-H bond are pulled toward oxygen. This creates partial charges that allow neighboring water molecules to attract each other through hydrogen bonds.

Question 17Basic Principles of Science

Joining two glucose molecules to form maltose releases a molecule of water. This reaction is best classified as which of the following?

  1. oxidation
  2. dehydration synthesis Correct answer.
  3. neutralization
  4. hydrolysis

Explanation

Dehydration synthesis joins monomers by removing a water molecule, forming a covalent bond between them. Hydrolysis is the reverse process, in which water is added to break a bond.

Question 18Basic Principles of Science

A buffer helps maintain a stable pH by doing which of the following?

  1. accepting or releasing hydrogen ions as conditions change Correct answer.
  2. raising the pH to exactly 7 at all times
  3. preventing any chemical reaction from occurring in the solution
  4. removing all hydrogen ions from solution

Explanation

A buffer is a system that resists large pH changes by accepting hydrogen ions when they are in excess and releasing them when they are depleted. It does not remove all hydrogen ions, force a pH of 7, or stop chemical reactions.

Question 19Basic Principles of Science

A study finds that towns with more ice cream sales also have more drowning deaths. Which conclusion is most justified?

  1. correlation exists, but causation is not established Correct answer.
  2. the data prove that one variable directly causes the other
  3. drowning causes increased ice cream sales
  4. the mean is smaller than the median for this data set

Explanation

An observed association between two variables is a correlation and does not by itself establish cause and effect. A third factor, such as warm summer weather, could influence both ice cream sales and swimming-related drownings.

Question 20Basic Principles of Science

A researcher gives a new supplement to volunteers who also begin a daily exercise program, then observes improved health. Which is the main flaw in this design?

  1. exercise is a confounding variable Correct answer.
  2. the sample was too large
  3. there is no dependent variable
  4. the hypothesis was not stated

Explanation

Exercise changed at the same time as the supplement, so any health improvement cannot be attributed to the supplement alone. Exercise is a confounding variable that should be controlled by comparing groups that differ only in supplement use.

Question 21Basic Principles of Science

Which recorded volume implies the most precise measuring instrument?

  1. 12.000 mL Correct answer.
  2. 12 mL
  3. 12.0 mL
  4. 12.00 mL

Explanation

A measurement with more decimal places implies that the instrument can resolve smaller increments. Of the choices, 12.000 mL carries the most significant figures and thus indicates the greatest measurement precision.

Question 22Basic Principles of Science

An enzyme that normally functions at pH 7 is placed in a pH 2 solution and loses activity. What is the most likely explanation?

  1. the enzyme's shape was altered, changing its active site Correct answer.
  2. the substrate concentration in the solution increased sharply
  3. the reaction became endergonic
  4. the enzyme was converted into a carbohydrate

Explanation

Extreme pH can disrupt the bonds that maintain an enzyme's three-dimensional shape, altering the active site so the substrate no longer binds properly. This denaturation explains the loss of activity; enzymes are not converted into carbohydrates.

Question 23Basic Principles of Science

For the data set 10, 12, 12, 13, 45, which statement is correct?

  1. the median is 12 and is resistant to the outlier Correct answer.
  2. the mode of the data set is 45 because it appears only once
  3. the mean is 12
  4. the mean is smaller than the median for this data set

Explanation

The median is the middle value of the ordered data, which is 12. The mean is 18.4 because the value 45 pulls it upward, so the median is less affected by that outlier. The mode is 12, not 45.

Question 24Basic Principles of Science

A survey about library hours is distributed only to students who visit the library at night. Which is the main problem with this survey?

  1. the survey lacks a control group
  2. the data are qualitative rather than quantitative
  3. the sample is biased and may not represent all students Correct answer.
  4. the sample size is too large

Explanation

Sampling only night-time library visitors selects a group that may differ systematically from the broader student population. This biases the results and limits how well they generalize to all students.

Question 25Molecular and Cellular Biology

The tendency of water molecules to stick together and form a continuous column in plant xylem is best explained by which property?

  1. The nonpolar nature of the oxygen atom
  2. Repulsion between dissolved ions
  3. The high molecular mass of water
  4. Hydrogen bonding between water molecules Correct answer.

Explanation

Each water molecule can hydrogen bond with up to four neighbors, and these interactions produce cohesion, the attraction of water molecules to one another. Cohesion lets water withstand tension in a narrow xylem vessel without the column breaking. Adhesion to the vessel walls supplements cohesion.

Question 26Molecular and Cellular Biology

The joining of two amino acids during protein synthesis releases a water molecule. This reaction is best described as

  1. a hydrolysis reaction that cleaves a polymer
  2. a condensation reaction that forms a covalent bond Correct answer.
  3. a redox reaction that transfers electrons
  4. an isomerization that rearranges the carbon skeleton

Explanation

A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of the next, releasing water. Reactions that build polymers while releasing water are condensation (dehydration synthesis) reactions. The resulting C–N bond is covalent.

Question 27Molecular and Cellular Biology

Why do phospholipids spontaneously form a bilayer in aqueous solution?

  1. Phosphate heads are hydrophobic and cluster together
  2. Covalent bonds form between adjacent phospholipid molecules
  3. Hydrophilic heads face water and hydrophobic tails face inward Correct answer.
  4. Fatty acid tails are attracted to water by hydrogen bonds

Explanation

Phospholipids are amphipathic: the phosphate head is polar and interacts with water, while the two fatty acid tails are nonpolar and are excluded by water. The lowest-energy arrangement buries the tails in the interior and exposes the heads to water on both faces, producing a bilayer. The structure is stabilized by hydrophobic interactions rather than by bonds between lipids.

Question 28Molecular and Cellular Biology

A drug resembles the substrate of an enzyme and binds reversibly at the active site. Adding more substrate restores the reaction rate. This inhibition is best classified as

  1. noncompetitive
  2. irreversible
  3. uncompetitive
  4. competitive Correct answer.

Explanation

A competitive inhibitor competes with substrate for the active site, so raising substrate concentration outcompetes the inhibitor and restores the maximal rate. The inhibitor binds reversibly, so the enzyme is not permanently inactivated. This pattern distinguishes competitive from other inhibition types.

Question 29Molecular and Cellular Biology

Which statement best explains why a given enzyme usually catalyzes only one type of reaction?

  1. Enzymes lower the activation energy of every reaction they contact
  2. Enzymes raise the free energy of the products
  3. Its active site is complementary in shape to its substrate Correct answer.
  4. Enzymes are consumed in the reaction and must be replaced

Explanation

Specificity arises because the active site's geometry and chemical environment fit only certain substrates, forming an enzyme–substrate complex. Molecules that do not fit cannot be stabilized in the transition state. This complementarity, not a general catalytic effect, accounts for specificity.

Question 30Molecular and Cellular Biology

A solute crosses a plasma membrane down its concentration gradient through a channel protein without any ATP consumption. This movement is best described as

  1. endocytosis
  2. primary active transport
  3. secondary active transport
  4. facilitated diffusion Correct answer.

Explanation

Facilitated diffusion uses a membrane protein to let a solute pass down its electrochemical gradient without energy input. Because the driving force is the gradient itself, the process is passive. It differs from active transport, which requires energy to move solutes against a gradient.

Question 31Molecular and Cellular Biology

A plant cell is placed in a hypertonic solution. Which prediction best describes the immediate result?

  1. Water enters the cell and turgor pressure rises
  2. The cell swells until it lyses
  3. Solutes move into the cell by active transport
  4. Water leaves the cell and the protoplast shrinks Correct answer.

Explanation

In a hypertonic solution the surrounding fluid has a lower water potential, so water exits the cell by osmosis. In a plant cell the plasma membrane pulls away from the rigid wall, a condition called plasmolysis. Turgor pressure falls rather than rises.

Question 32Molecular and Cellular Biology

The Na+/K+ ATPase exports three Na+ ions and imports two K+ ions per ATP hydrolyzed. This transport is best classified as

  1. primary active transport of both ions against their gradients Correct answer.
  2. facilitated diffusion driven by a concentration gradient
  3. simple diffusion through the lipid bilayer
  4. cotransport of both ions in the same direction

Explanation

The pump hydrolyzes ATP to move both ions against their electrochemical gradients, which makes it primary active transport. Because the ions travel in opposite directions, the mechanism is antiport rather than cotransport. Energy from ATP is required because the gradients are being built, not dissipated.

Question 33Molecular and Cellular Biology

Where in a eukaryotic cell does glycolysis take place?

  1. In the nucleus
  2. In the cytosol Correct answer.
  3. On the inner mitochondrial membrane
  4. In the mitochondrial matrix

Explanation

Glycolysis enzymes are soluble in the cytoplasm, so the pathway occurs in the cytosol. Its products, pyruvate and NADH, are then transported into the mitochondrion for further oxidation. Compartmentalization separates glycolysis from the later oxidative stages.

Question 34Molecular and Cellular Biology

Per turn, the citric acid cycle yields which set of products?

  1. 2 ATP, 6 NADH, and 2 FADH2 per turn
  2. 6 CO2, 6 H2O, and light energy
  3. 1 ATP, 3 NADH, 1 FADH2, and 2 CO2 Correct answer.
  4. 2 pyruvate, 2 NADH, and 2 ATP per turn

Explanation

One turn of the cycle oxidizes one acetyl group, releasing two carbons as CO2 and reducing three NAD+ and one FAD. Substrate-level phosphorylation produces one ATP (GTP in some tissues). Because one glucose yields two acetyl-CoA, the per-glucose totals are double these values.

Question 35Molecular and Cellular Biology

ATP synthase in mitochondria produces ATP using which immediate energy source?

  1. Oxidation of pyruvate by the PDH complex
  2. A proton gradient across the inner membrane Correct answer.
  3. Hydrolysis of GTP in the matrix
  4. Electron transfer from NADH to oxygen

Explanation

Electron transport pumps protons into the intermembrane space, creating an electrochemical gradient. Protons flowing back through ATP synthase drive rotation of the enzyme and the phosphorylation of ADP. The gradient, not electron transfer itself, is the direct energy source for the enzyme.

Question 36Molecular and Cellular Biology

What is the primary role of fermentation in cells such as exercising muscle fibers?

  1. It regenerates NAD+ so glycolysis can continue Correct answer.
  2. It completely oxidizes pyruvate to carbon dioxide
  3. It generates NADPH for biosynthetic reactions
  4. It produces large amounts of ATP per glucose

Explanation

When oxygen is limiting, the electron transport chain cannot reoxidize NADH, so NAD+ would run out and glycolysis would stall. Fermentation transfers electrons from NADH to pyruvate or a derivative, regenerating NAD+. The ATP yield comes only from glycolysis.

Question 37Molecular and Cellular Biology

Which products of the light reactions are consumed in the Calvin cycle?

  1. ATP and pyruvate
  2. NADH and FADH2
  3. O2 and glucose
  4. ATP and NADPH Correct answer.

Explanation

The light reactions convert light energy into the chemical energy of ATP and NADPH. The Calvin cycle spends both to reduce CO2 into carbohydrate. Oxygen is released by the light reactions, and glucose is a product of the Calvin cycle rather than an input.

Question 38Molecular and Cellular Biology

The enzyme that catalyzes carbon fixation in the Calvin cycle is

  1. ATP synthase
  2. RuBisCO Correct answer.
  3. pyruvate dehydrogenase
  4. phosphofructokinase

Explanation

RuBisCO attaches CO2 to ribulose-1,5-bisphosphate, splitting the product into two molecules of 3-phosphoglycerate. This is the committed step of the Calvin cycle and the most abundant enzyme on Earth. Its oxygenase activity also initiates photorespiration.

Question 39Molecular and Cellular Biology

In double-stranded DNA, how many hydrogen bonds link adenine to thymine and guanine to cytosine?

  1. A–T: two; G–C: one
  2. A–T: three; G–C: three
  3. A–T: three; G–C: two
  4. A–T: two; G–C: three Correct answer.

Explanation

Adenine and thymine form two hydrogen bonds, while guanine and cytosine form three. Because G–C pairs have more hydrogen bonds and greater stacking interactions, GC-rich regions melt at higher temperatures. This base-pairing rule underlies Chargaff's ratios.

Question 40Molecular and Cellular Biology

DNA replication is described as semiconservative because

  1. repair enzymes replace damaged bases with new ones
  2. each new DNA molecule contains only newly synthesized strands
  3. each daughter duplex has one parental and one new strand Correct answer.
  4. only the leading strand is synthesized continuously

Explanation

Each parental strand serves as a template, so every product duplex retains one original strand paired with one newly made strand. This was demonstrated by the Meselson–Stahl density-shift experiment. The term describes the fate of the parental strands, not the mechanics of the fork.

Question 41Molecular and Cellular Biology

DNA polymerase makes the lagging strand as short Okazaki fragments. Which statement best explains why?

  1. Helicase unwinds the lagging strand template in the 3'-to-5' direction only
  2. DNA polymerase extends only from a 3' end, opposite the fork's direction Correct answer.
  3. The lagging strand template contains uracil in place of thymine bases
  4. DNA ligase can join only fragments longer than about 1000 nucleotides

Explanation

DNA polymerase adds nucleotides only to a free 3'-OH and therefore extends 5' to 3'. On the lagging strand template, the permissive direction points away from the advancing fork, so synthesis must restart repeatedly as new template is exposed. Ligase later seals the resulting fragments.

Question 42Molecular and Cellular Biology

In eukaryotic cells, messenger RNA is synthesized by which enzyme?

  1. Reverse transcriptase
  2. RNA polymerase II Correct answer.
  3. The ribosome
  4. DNA polymerase III

Explanation

RNA polymerase II transcribes protein-coding genes into pre-mRNA, which is then processed. RNA polymerase I makes rRNA and RNA polymerase III makes tRNA and small RNAs. Only RNA polymerase II produces the mRNA template for translation.

Question 43Molecular and Cellular Biology

During mRNA processing in eukaryotes, introns are removed and exons are joined together by which structure?

  1. Poly-A polymerase
  2. The primase complex
  3. The ribosome
  4. The spliceosome Correct answer.

Explanation

The spliceosome is a complex of small nuclear RNAs and proteins that recognizes splice sites, catalyzes intron removal, and ligates exons. Alternative splicing by the same machinery lets one gene encode multiple protein variants. Capping and polyadenylation are separate processing events.

Question 44Molecular and Cellular Biology

A tRNA carries the anticodon 3'-UAC-5'. Which mRNA codon does it recognize?

  1. 5'-GUA-3'
  2. 5'-UAC-3'
  3. 5'-CAU-3'
  4. 5'-AUG-3' Correct answer.

Explanation

Anticodon and codon pair antiparallel and complementary, so the anticodon read 3' to 5' matches the codon read 5' to 3'. Reading 3'-UAC-5' as its complement gives 5'-AUG-3', the start codon. This tRNA therefore carries methionine to the ribosome.

Question 45Molecular and Cellular Biology

A point mutation changes a codon from 5'-GCA-3' to 5'-GCG-3', yet the encoded protein is unchanged. Which statement best explains this result?

  1. The mutation converted a stop codon into a sense codon, preserving the protein
  2. The ribosome proofread and corrected the error during translocation along the mRNA
  3. The code is degenerate; several codons specify the same amino acid Correct answer.
  4. The mutation occurred within an intron and was removed by splicing before translation

Explanation

GCA and GCG both specify alanine, so replacing the third base does not alter the amino acid sequence; such a change is a silent mutation. The wobble position of a codon is frequently tolerant of substitution for this reason. The protein is unchanged because the same amino acid is inserted.

Question 46Molecular and Cellular Biology

In the lac operon, the repressor binds the operator and blocks transcription. When lactose is available, transcription rises because

  1. RNA polymerase binds to the operator region more tightly than before
  2. catabolite activator protein is rapidly degraded when glucose is present
  3. lactose binds the repressor, lowering its affinity for the operator Correct answer.
  4. the promoter is deleted from the DNA before transcription begins

Explanation

Lactose is converted to allolactose, which binds the repressor and causes a conformational change that releases it from the operator. RNA polymerase can then bind the promoter and transcribe the operon. This is negative control relieved by an inducer.

Question 47Molecular and Cellular Biology

During which phase of mitosis do sister chromatids separate and move toward opposite poles?

  1. Anaphase Correct answer.
  2. Metaphase
  3. Prophase
  4. Telophase

Explanation

In anaphase the cohesin holding sister chromatids together is cleaved, and motor proteins pull the now individual chromosomes along spindle microtubules toward the poles. Prophase and metaphase precede separation, and telophase follows it as nuclei re-form. The transition is triggered by activation of the anaphase-promoting complex.

Question 48Molecular and Cellular Biology

An organism has a diploid number of 2n = 8. Counting only independent assortment of whole chromosomes, how many genetically distinct gamete types can it produce?

  1. 4
  2. 16 Correct answer.
  3. 32
  4. 8

Explanation

The number of assortment combinations equals 2 raised to the haploid number, because each of the n homologous pairs orients independently. Here n = 4, so 2^4 = 16 combinations. Crossing over would increase the total further.

Question 49Molecular and Cellular Biology

Entry into mitosis requires activation of CDK1 by cyclin B. Which observation best supports the conclusion that cyclin B is the limiting regulator of this transition?

  1. Cells in G1 lack condensed chromosomes and an assembled spindle
  2. Injecting cyclin B into G2 cells speeds entry into mitosis Correct answer.
  3. CDK1 concentration stays nearly constant through the cell cycle
  4. Cyclin B is ubiquitylated and destroyed by the proteasome after mitosis

Explanation

If adding cyclin B is sufficient to accelerate the transition, then cyclin availability, not CDK abundance, is the rate-limiting factor. CDKs are present throughout the cycle and become active only when their cyclin partners appear. This is the logic of a regulatory subunit controlling an enzyme.

Question 50Molecular and Cellular Biology

Which component forms the hydrophobic barrier that prevents most polar molecules from freely crossing a plasma membrane?

  1. The glycocalyx
  2. Peripheral membrane proteins
  3. The phospholipid bilayer Correct answer.
  4. Integral membrane channels

Explanation

The phospholipid bilayer is arranged with hydrophobic fatty acid tails facing inward, creating a barrier to polar and charged solutes. Proteins and carbohydrates contribute to membrane function but do not form this continuous hydrophobic core.