2 questions, one for each idea where we can. Answer them, then see which ideas to fix.
Question 1 of 2
Which statement best describes compartmentalization in a eukaryotic cell?
Answer and reasoning
AMembranes enclose regions in which particular enzymes and reactions are kept separate.Correct Internal membranes and membrane-bound organelles divide the cell into compartments, each holding its own enzymes and conditions, so particular metabolic processes and enzymatic reactions take place in particular places.
BEach compartment is sealed so that no molecules pass between it and the cytosol. A student who thinks compartments are sealed off picks this. Membranes are selectively permeable; materials move between compartments through transport proteins and in vesicles.
CEnzymes move freely between organelles so that every reaction can happen anywhere in the cell. A student who pictures the cell as a uniform bag of enzymes picks this. Compartmentalization does the opposite: it keeps particular enzymes and reactions in particular places.
DOrganelles store materials, while all of the cell's reactions take place in the cytosol. A student who thinks organelles are only storage containers picks this. Many reactions occur inside organelles or on their membranes, such as digestion in lysosomes and ATP synthesis in mitochondria.
The model shows where two pathways occur in a hypothetical animal cell. Based on the model, which statement about this arrangement is best supported?
Answer and reasoning
AFatty acids made in the cytosol are sealed off from the mitochondria for good. A student who thinks compartments are sealed picks this. Membranes are selectively permeable; fatty acids can be moved into mitochondria when they are to be broken down.
BNewly made fatty acids are kept from the enzymes that break them down.Correct The product of one pathway (fatty acids) is the substrate of the other. Placing the synthesis enzymes in the cytosol and the breakdown enzymes inside mitochondria minimizes competing interactions, so newly made fatty acids are not immediately broken down again.
CEach compartment decides which pathway to run, based on what the cell needs. A student who explains cell processes by choice or need picks this. Which pathway occurs where depends on which enzymes are present in each compartment.
DSeparating them has no effect, as each enzyme acts on its own substrate only. A student who thinks enzyme specificity alone prevents interference picks this. The breakdown enzymes' substrate is the synthesis pathway's product, so in one compartment the two pathways would undo each other.
In preparation: 0 of 2 sections compiled and reviewed. The rest show key terms and common mistakes from our question bank until they are.
2.9.A.1 Compartmentalization Fix
Compartmentalization
The division of a eukaryotic cell by membranes into separate regions (compartments), each with its own set of enzymes and conditions, so that particular metabolic processes and enzymatic reactions take place in particular places.
Membrane-bound organelle
A structure in a eukaryotic cell enclosed by one or two membranes, such as the nucleus, endoplasmic reticulum, Golgi complex, lysosome, vacuole, mitochondrion or chloroplast. Ribosomes are not enclosed by a membrane.
Different conditions in different compartments
Because membranes separate compartments, each can keep its own internal conditions. For example, the inside of a lysosome is acidic (about pH 5), while the surrounding cytosol is close to neutral (about pH 7.2).
Lysosome
A membrane-enclosed sac containing hydrolytic enzymes that digest macromolecules and other material delivered to it. Its membrane keeps these enzymes apart from the rest of the cell.
Students often think Each membrane-bound compartment is sealed, so no molecules can pass between it and the rest of the cell. In fact No. Membranes are selectively permeable, and materials move between compartments through transport proteins and in vesicles. Compartments separate reactions without isolating them completely.
Students often think A cell is a uniform bag of enzymes: any enzyme acts equally well wherever it is, and membranes do not limit what it can reach. In fact No. An enzyme's activity depends on its surroundings, such as pH, and on whether its substrate can reach it. Compartments give enzymes particular conditions and keep them with or away from particular substrates.
2.9.B.1 Minimizing competing interactions Fix
Minimizing competing interactions
Separating reactions or enzymes that would interfere with each other, for example a pathway that builds a molecule and one that breaks it down, so that both can operate without undoing each other's work.
Internal membrane surface area
Folded or extensive internal membranes provide a large area on which membrane-bound enzymes and other proteins can carry out reactions, so more reactions can occur at once in a given volume.
Inner mitochondrial membrane
The highly folded inner membrane of a mitochondrion. Its folds increase the surface area available for the membrane-bound reactions of aerobic cellular respiration that synthesize ATP.
Rough ER surface
The membrane of the rough endoplasmic reticulum, studded with ribosomes that synthesize proteins, including proteins for secretion. A larger area of rough ER membrane provides room for more bound ribosomes.
Students often think If two variables change together, or one group differs from another, the data prove that one variable causes the other and is the only factor involved. In fact No. Correlation can suggest a causal link but does not prove it; another factor could cause both, or the direction of cause could be the reverse. Even experimental data support a claim rather than prove it, and rarely show that one factor is the only one involved.
Students often think Organelles and cells choose which reactions to run, and work harder when they need more of something. In fact No. Which reactions occur in a compartment depends on which enzymes are present there and which substrates reach it. Cells regulate this through molecular mechanisms, not by deciding or by working harder in response to need.
5 more questions. Every wrong answer here is a real mistake students make, and you see why it is wrong as soon as you answer.
Question 1 of 5
The graph shows the relative activity of two enzymes from a hypothetical animal cell at different pH values. Enzyme L is found inside lysosomes, where the pH is about 5; enzyme C is found in the cytosol, where the pH is about 7. Which claim is best supported by the data?
Answer and reasoning
AEnzyme L would digest material in the cytosol as fast as in a lysosome, wherever in the cell it is. A student who thinks an enzyme acts equally well anywhere in the cell picks this. The data show L's activity falls to about 20% at the cytosol's pH of 7.
BEnzyme L has no activity at pH 7, so L that leaked into the cytosol could do no harm to the cell. A student who thinks an enzyme works only at its optimum picks this. The graph shows L still has about 20% of its maximum activity at pH 7, not zero.
CEnzyme L is much less active at pH 7, so L that leaked into the cytosol would act far more slowly.Correct Enzyme L's activity is 100% at pH 5, the pH inside lysosomes, but only about 20% at pH 7, the pH of the cytosol. Keeping L in the acidic lysosome lets it work at full activity, and any L that escapes into the cytosol works much more slowly.
DEnzyme L causes the low pH inside lysosomes, since L is most active at a low pH of about 5. A student who reads correlation as causation picks this. The data show only how L's activity depends on pH; they say nothing about what sets the pH of the lysosome.
Mitochondria were isolated from wild-type cells and from two mutant strains of a hypothetical yeast whose mitochondria have fewer folds in their inner membranes. The graph shows the mean rate of ATP synthesis per mitochondrion, with error bars showing ±2 SE of the mean, and the relative inner membrane area per mitochondrion of each strain. Which conclusion is best supported by the data?
Answer and reasoning
AMutant Y made ATP more slowly than mutant X, as mutant Y's mean is the lower of the two. A student who treats any difference in means as real picks this. The two mutants' ±2 SE bars overlap, so the data do not show that their rates differ.
BMutants X and Y make ATP at exactly the same rate, as the error bars of these two overlap. A student who thinks overlapping bars prove equal means picks this. Overlap shows only that no difference was detected; the two rates could still differ.
CThe data prove that inner membrane area is the only factor setting the rate of ATP synthesis. A student who thinks data can prove a single cause picks this. The mutations could affect more than membrane area, and the data support, rather than prove, a link between area and rate.
DBoth mutants made ATP more slowly than the wild type, as their error bars lie well below it.Correct The wild type's ±2 SE interval (6.2–7.4) does not overlap either mutant's (3.4–4.4 and 2.9–4.1), so both mutants very likely make ATP more slowly. This fits the idea that a smaller inner membrane area provides less surface for the membrane-bound reactions.
Working Mean ± 2 SE: wild type 6.8 (6.2–7.4); mutant X 3.9 (3.4–4.4); mutant Y 3.5 (2.9–4.1). Each mutant's interval lies well below the wild type's, with no overlap, so both differences are likely significant. The mutant X and mutant Y intervals overlap (3.4–4.4 and 2.9–4.1), so the data do not show a difference between the two mutants, nor do they show that the two are equal.
Lysosomes contain hydrolytic enzymes that can break down proteins, lipids, nucleic acids and polysaccharides. Which statement best describes the role of the lysosome's membrane in the cell?
Answer and reasoning
AIt stores the enzymes in an inactive form until they are released to digest material in the cytosol. A student who thinks organelles are only storage containers picks this. Lysosomal enzymes digest material inside the lysosome; releasing them into the cytosol is not their normal role.
BIt protects the enzymes from being used up, as each enzyme molecule can act just once. A student who thinks enzymes are used up in reactions picks this. Enzymes are not consumed; each molecule catalyzes the same reaction many times.
CIt keeps the enzymes apart from the cell's own molecules, so they digest only material delivered to them.Correct The membrane separates the hydrolytic enzymes from the rest of the cell, minimizing competing interactions: the enzymes digest the material brought into the lysosome rather than the cell's own proteins, lipids and nucleic acids in the cytosol.
DIt supplies the enzymes with the food and oxygen that they need in order to stay alive. A student who thinks enzymes are living things picks this. Enzymes are molecules, not organisms, and do not need food or oxygen.
A student isolates a cell fraction containing intact membrane-bound organelles from a hypothetical animal cell and hypothesizes that enzyme E is enclosed inside one kind of organelle in this fraction. The substrate of E cannot cross membranes. E activity is measured in two samples of the fraction: one untreated, and one treated with a mild detergent that dissolves membranes but does not affect E. Which result would be predicted if the hypothesis is correct?
Answer and reasoning
AHigher E activity after detergent, as the substrate can then reach ECorrect If E is enclosed in an organelle, its substrate cannot reach it while the membranes are intact, so the untreated sample shows little activity. Dissolving the membranes gives the substrate access to E, so activity rises.
BLower E activity after detergent, as E needs an intact organelle to work A student who thinks an enzyme works only inside its intact organelle picks this. Releasing E does not stop it working; it lets the substrate reach it.
CThe same E activity in both, as membranes do not limit where E can act A student who thinks membranes do not affect what an enzyme can reach picks this. The substrate cannot cross membranes, so an enclosed E cannot act on it until the membranes are dissolved.
DNo E activity in either sample, as enzymes act only within living cells A student who thinks enzymes are alive and work only in living cells picks this. Enzymes catalyze reactions outside cells when conditions and substrate are suitable.
Cells of a hypothetical gland secrete large amounts of a digestive enzyme, which is a protein. A drug causes the rough ER of these cells to lose much of its folded membrane, greatly reducing its surface area, without affecting the ribosomes themselves. Which prediction about the amount of enzyme the cells make for secretion is best supported?
Answer and reasoning
AIt is unchanged, as proteins for secretion are made in the Golgi complex, not in the ER. A student who thinks the Golgi complex makes secreted proteins picks this. Secretory proteins are made by ribosomes on the rough ER; the Golgi complex modifies and packages them.
BIt falls to zero, as the ER membrane itself builds every protein made for secretion. A student who thinks the ER membrane itself makes proteins picks this. Ribosomes make the proteins; the reduced membrane still holds some ribosomes, so production falls but does not stop.
CIt increases, as the cells work harder to make up for the loss of so much of their ER. A student who thinks cells respond to need by working harder picks this. With less rough ER membrane there is less surface for bound ribosomes, so production falls.
DIt decreases, as there is less membrane to which the ribosomes that make it can bind.Correct The extensive membrane of the rough ER provides the surface on which ribosomes making secretory proteins are held. With much less membrane area, fewer such ribosomes can be bound, so less enzyme is made for secretion.
Compiled from the AP Biology Course and Exam Description (effective Fall 2025) and our question bank · Specialist review in progress. How these pages are made · Free, no account
