8 questions, one for each idea where we can. Answer them, then see which ideas to fix.
Question 1 of 8
Which statement correctly describes ribosomes?
Answer and reasoning
AThey are membrane-bound organelles, so they are found only in eukaryotic cells. A student who thinks ribosomes are membrane-bound organelles picks this. Ribosomes have no membrane, and prokaryotic cells have them.
BThey copy the DNA of genes into mRNA, which then carries the copy to the cytoplasm. A student who thinks ribosomes make mRNA picks this. Ribosomes read mRNA to synthesize proteins; mRNA is made from DNA by a different process.
CThey build the cell's proteins inside the nucleus, close to the genes that code for them. A student who thinks proteins are made in the nucleus picks this. Ribosomes synthesize proteins in the cytoplasm, either free or bound to rough ER; the nucleus holds the DNA.
DThey are made of rRNA and protein and are found in prokaryotic and eukaryotic cells.Correct Ribosomes are non-membrane structures made of ribosomal RNA and protein. They are found in the cells of all forms of life, where they synthesize proteins according to mRNA sequences.
In cells of a hypothetical mammal, newly made secretory proteins can be labeled and followed. Normally the label appears first in the rough ER, then in the Golgi complex, and then in secretory vesicles. The experiment is repeated with a chemical that prevents transport vesicles from budding off the ER but does not affect protein synthesis. Which result is predicted?
Answer and reasoning
AThe label stays in the rough ER and does not reach the Golgi complex or the secretory vesicles.Correct Proteins made on the rough ER reach the Golgi complex in transport vesicles that bud from the ER. With budding blocked, the labeled proteins are made but stay in the ER.
BThe label still reaches the Golgi complex, moving there through the cytosol instead. A student who thinks proteins travel through the cytosol by diffusion picks this. Secretory proteins are inside the ER and can leave it only in transport vesicles.
CThe label appears first in the Golgi complex, which makes the proteins in place of the ER. A student who thinks the Golgi complex makes proteins picks this. Proteins are synthesized by ribosomes on the rough ER; the Golgi complex receives them.
DThe label in the rough ER falls as fast as normal, as the trapped proteins are broken down. A student who reads a fall in label as breakdown picks this. Normally the label falls in the ER because proteins leave in vesicles; with vesicle budding blocked, the proteins are expected to remain in the ER.
Which statement describes general roles of the endoplasmic reticulum (ER) in a eukaryotic cell?
Answer and reasoning
AIt receives finished proteins from the Golgi complex, where the cell's proteins are synthesized. A student who thinks the Golgi complex makes proteins picks this. Proteins are made by ribosomes, including those on rough ER, and are then sent to the Golgi complex.
BIt supports the cell, helping it keep its shape, and plays a role in transport within the cell.Correct The ER is an extensive network of membranes that provides mechanical support, helping the cell maintain its shape, and plays a role in intracellular transport.
CIts entire membrane is covered with ribosomes, and every part of it is used to make proteins. A student who thinks all ER is rough ER picks this. Smooth ER has no bound ribosomes; its functions include detoxification and lipid synthesis.
DIt stores newly made proteins, which then diffuse through the cytosol to the places they are needed. A student who thinks proteins reach their destinations by diffusing through the cytosol picks this. Proteins made in the ER are carried in transport vesicles within the endomembrane system.
The model shows the path of a protein through part of a cell of a hypothetical animal. Based on the changes to the protein shown in the model, which statement best describes the role of structure Y?
Answer and reasoning
AIt chemically modifies the protein and packages it into a vesicle for transport.Correct In the model, the protein enters Y without a sugar chain and leaves Y in a new vesicle with a sugar chain attached. Y is the Golgi complex, which modifies newly made products and packages proteins for trafficking.
BIt synthesizes the protein by joining amino acids in the order coded by mRNA. A student who thinks the Golgi complex makes proteins picks this. The model shows the protein already made when it arrives at Y from the rough ER.
CIt releases the protein into the cytosol, to diffuse to the plasma membrane. A student who thinks proteins diffuse through the cytosol picks this. The model shows the protein leaving Y inside a vesicle, which carries it to the plasma membrane.
DIt returns the protein to the rough ER, where it is packaged for secretion. A student who thinks the ER packages proteins for secretion picks this. In the model the protein moves from the rough ER to Y and from Y toward the plasma membrane, not back to the ER.
Researchers measured the average area of the inner mitochondrial membrane per mitochondrion and the rate of ATP synthesis per mitochondrion in six cell types of a hypothetical animal. The graph shows the results. Which statement best describes the data?
Answer and reasoning
AThe data show that high rates of ATP synthesis cause the inner membrane to fold. A student who takes a correlation as proof of cause picks this. The data show that the two variables increase together; they do not show which, if either, causes the other.
BDoubling the inner membrane area per mitochondrion doubled the rate of ATP synthesis. A student who assumes the relationship is proportional picks this. When the area doubled from 8 to 16 μm², the rate rose from 2.0 to 3.1 units, not to 4.0; from 12 to 24 μm² it rose from 2.4 to 3.9, not to 4.8.
CCell types with more inner membrane area stored more ATP in the folds of that membrane. A student who thinks the folds store ATP picks this. The graph shows the rate of ATP synthesis, not an amount of stored ATP.
DCell types with more inner membrane area per mitochondrion had higher rates of ATP synthesis.Correct The points rise from left to right: as inner membrane area increases from 8 to 28 μm², the rate of ATP synthesis increases from 2.0 to 4.2 arbitrary units, a positive relationship.
A white blood cell takes in a bacterium by enclosing it in a vesicle formed from the plasma membrane. A lysosome then fuses with the vesicle. Which statement best describes how the bacterium's macromolecules are then broken down?
Answer and reasoning
AHydrolytic enzymes from the lysosome break their bonds, releasing water molecules. A student who mixes up hydrolysis and dehydration synthesis picks this. Hydrolysis uses water to break bonds; water is released when bonds form.
BHydrolytic enzymes from the lysosome are used up, one molecule for each bond broken. A student who thinks enzymes are used up in reactions picks this. Each enzyme molecule is unchanged by the reaction and breaks many bonds, one after another.
CMitochondria take in the macromolecules and break them down to release energy. A student who thinks mitochondria digest engulfed material picks this. The bacterium is digested by the lysosome's hydrolytic enzymes inside the fused vesicle.
DHydrolytic enzymes from the lysosome break their bonds by adding water to each one.Correct Lysosomes contain hydrolytic enzymes. When the lysosome fuses with the vesicle, these enzymes break the bonds in the bacterium's macromolecules by hydrolysis, adding a water molecule across each bond.
Which statement correctly describes vacuoles in animal cells?
Answer and reasoning
AAnimal cells have many vacuoles, smaller than in plant cells, that store materials.Correct In animal cells, vacuoles are smaller and more plentiful than in plant cells, and they store cellular materials.
BAnimal cells have no vacuoles, as vacuoles are found only in the cells of plants. A student who thinks vacuoles are a plant-only feature picks this. Animal cells have vacuoles; they are smaller and more numerous than the plant central vacuole.
CAnimal cells have one large central vacuole that keeps them firm by turgor pressure. A student who applies the plant-cell model to animal cells picks this. Turgor pressure needs a cell wall to press against, and animal cells have many small vacuoles, not one large one.
DAnimal cells have many small vacuoles, which are sacs that hold water and nothing else. A student who thinks vacuoles are just water bags picks this. Animal-cell vacuoles store a variety of cellular materials.
The diagram shows an organelle from a eukaryotic cell, with its internal membranes simplified. Which statement correctly describes where this organelle is found and what it does?
Answer and reasoning
AIn plants, algae and photosynthetic bacteria; it is where photosynthesis occurs. A student who thinks every photosynthetic organism has chloroplasts picks this. Bacteria are prokaryotes and have no membrane-bound organelles; photosynthetic bacteria photosynthesize without chloroplasts.
BIn plants and photosynthetic algae; it is the site of photosynthesis.Correct The double membrane and the stacks of internal membrane sacs identify a chloroplast. Chloroplasts are found in plants and photosynthetic algae and are where photosynthesis takes place.
CIn plant cells, replacing mitochondria; it carries out cellular respiration. A student who thinks plants have chloroplasts instead of mitochondria picks this. Plant cells also have mitochondria, which carry out cellular respiration; the chloroplast carries out photosynthesis.
DIn every cell of a plant, including root cells; it carries out photosynthesis. A student who thinks every plant cell has chloroplasts picks this. Chloroplasts occur mainly in cells of green, light-exposed parts such as leaves; most root cells have none.
In preparation: 0 of 8 sections compiled and reviewed. The rest show key terms and common mistakes from our question bank until they are.
2.1.A.1 Ribosome Fix
Ribosome
A non-membrane structure made of ribosomal RNA (rRNA) and protein that synthesizes proteins according to the sequence of a messenger RNA (mRNA). Ribosomes are found in the cells of all forms of life.
Ribosomal RNA (rRNA)
The RNA that, together with proteins, makes up ribosomes.
Messenger RNA (mRNA)
The RNA whose sequence a ribosome reads to determine the order of amino acids in the protein it makes.
Ribosomes as evidence of common ancestry
Ribosomes of all known organisms share the same basic composition (rRNA and protein) and function, which reflects descent of all known life from a common ancestor.
Students often think Ribosomes are membrane-bound organelles, so prokaryotic cells, which lack membrane-bound organelles, have no ribosomes. In fact Yes. Ribosomes are not enclosed by membranes; they are made of rRNA and protein and are found in the cells of all forms of life, prokaryotes as well as eukaryotes.
Students often think A structure appears in a group of organisms because the organisms need it to survive. In fact No. Structures arise through heritable variation acted on by natural selection over many generations, not because organisms need them. A structure shared by all groups is best explained by inheritance from a common ancestor.
2.1.A.2 Endomembrane system Fix
Endomembrane system
A group of membrane-bound organelles and structures (endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, transport vesicles, the nuclear envelope and the plasma membrane) that work together to modify, package and transport polysaccharides, lipids and proteins.
Transport vesicle
A small membrane sac that buds from one membrane of the endomembrane system and carries its contents to another, such as from the ER to the Golgi complex or from the Golgi complex to the plasma membrane.
Students often think When the amount of labeled protein in an organelle falls, the protein is being broken down in that organelle. In fact Not necessarily. In a labeling experiment, a fall in the label in one compartment while it rises in another shows that the proteins have moved on; breakdown would show as a loss of label overall.
Students often think Proteins made in the ER travel through the cytosol by diffusion to the Golgi complex and to the cell surface. In fact No. Proteins made on the rough ER are kept inside the endomembrane system and are carried between its compartments in transport vesicles that bud from one membrane and fuse with another.
2.1.A.3 Endoplasmic reticulum (ER) Fix
Endoplasmic reticulum (ER)
A network of membrane sacs and tubes in eukaryotic cells that provides mechanical support, helping the cell keep its shape, and plays a role in transport within the cell. It has rough and smooth regions.
Rough ER
ER with membrane-bound ribosomes on its surface. It helps carry out protein synthesis, including synthesis of proteins that are secreted, and separates these proteins from the cytosol, compartmentalizing the cell.
Smooth ER
ER without bound ribosomes. Its functions include detoxification and the synthesis of lipids.
Detoxification
The chemical conversion of harmful substances into less harmful forms or forms that the cell can remove; one function of smooth ER.
Students often think All endoplasmic reticulum is covered with ribosomes and makes proteins; rough and smooth ER do the same job. In fact No. Rough ER has membrane-bound ribosomes and helps carry out protein synthesis; smooth ER has no bound ribosomes, and its functions include detoxification and lipid synthesis.
Students often think Any difference between two sample means shows a real (significant) difference between the groups. In fact No. Sample means vary by chance. With ±2 SE error bars, overlapping bars mean that a difference has not been shown to be significant.
2.1.A.4 Golgi complex Fix
Golgi complex
A membrane-bound organelle made of a series of flattened membrane sacs. It correctly folds and chemically modifies newly synthesized products and packages proteins into vesicles for trafficking.
Chemical modification in the Golgi (for example, glycosylation)
Changes made to newly synthesized products in the Golgi, such as adding sugar chains to proteins (glycosylation), that can determine a protein's function or where it is sent.
Protein trafficking
The packaging of proteins into vesicles and their delivery to their destinations, such as the plasma membrane for secretion or other organelles.
Students often think The Golgi complex makes proteins, which are then sent on to the endoplasmic reticulum. In fact No. Proteins are synthesized by ribosomes, including those on the rough ER. The Golgi complex receives newly made products, chemically modifies them, folds them correctly, and packages proteins into vesicles for trafficking.
Students often think The endoplasmic reticulum, not the Golgi complex, packages proteins into vesicles for secretion from the cell. In fact No. Vesicles from the ER carry proteins to the Golgi complex. The Golgi complex modifies proteins and packages them into the vesicles that carry them to their destinations, such as the plasma membrane.
2.1.A.5 Mitochondrion Fix
Mitochondrion
An organelle with a double membrane in which aerobic cellular respiration takes place. The membranes create compartments for different metabolic reactions.
Inner mitochondrial membrane
The highly convoluted inner membrane of a mitochondrion; its folds increase its surface area, which enables ATP to be synthesized more efficiently. The outer membrane is smooth.
Students often think When two variables are correlated, the data show that one causes the other. In fact No. A correlation shows that two variables change together; it does not by itself show that one causes the other, or in which direction any effect runs.
Students often think The outer membrane of a mitochondrion is the folded one, and the inner membrane is smooth. In fact The inner membrane is highly convoluted, forming folds; the outer membrane is smooth.
2.1.A.6 Lysosome Fix
Lysosome
A membrane-enclosed sac containing hydrolytic enzymes that digest material such as engulfed particles and worn-out cell parts. Lysosomes are also involved in apoptosis, the programmed death of a cell.
Hydrolytic enzyme
An enzyme that breaks covalent bonds in macromolecules by hydrolysis, adding water across each bond.
Apoptosis
Programmed cell death: an orderly process by which a cell destroys itself, in which lysosomes play a role.
Students often think When macromolecules are broken down, water is released at each bond that is broken. In fact No. Hydrolysis uses water: a water molecule is added across each bond that is broken. Water is released when bonds form by dehydration synthesis.
Students often think Each enzyme molecule is used up when it breaks a bond, so one enzyme molecule is needed for every bond broken. In fact No. Enzymes are catalysts: an enzyme molecule is not consumed by the reaction and can break many bonds, one after another.
2.1.A.7 Vacuole Fix
Vacuole
A membrane-bound sac that plays different roles in different cells, such as storing water, nutrients or other cellular materials.
Central vacuole and turgor pressure
The specialized large vacuole of a plant cell stores water and nutrients; the water it holds presses the cell membrane against the cell wall, maintaining turgor pressure, which keeps the cell firm.
Vacuoles in animal cells
In animal cells, vacuoles are smaller and more plentiful than in plant cells, and they store cellular materials.
Students often think The percent decrease is the new value expressed as a percentage of the original value (new/original × 100). In fact Percent change = (new value − original value)/original value × 100. A negative result is a decrease.
Students often think The percent change is the difference between the two values, written with a percent sign. In fact No. A percent change compares the size of the change with the original value: (change/original) × 100.
2.1.A.8 Chloroplast Fix
Chloroplast
A specialized organelle with a double membrane found in plants and photosynthetic algae; it is the location of photosynthesis.
Students often think Every organism that carries out photosynthesis, including photosynthetic bacteria, does so in chloroplasts. In fact No. Chloroplasts are membrane-bound organelles found in plants and photosynthetic algae. Photosynthetic prokaryotes carry out photosynthesis on their own membranes but have no chloroplasts.
Students often think Plant cells have chloroplasts in place of mitochondria, and chloroplasts carry out the plant's cellular respiration. In fact No. Plant cells have mitochondria and carry out aerobic cellular respiration; many plant cells also have chloroplasts, which carry out photosynthesis. Photosynthesis does not replace respiration.
9 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 9
Cells of bacteria, archaea and eukaryotes all contain ribosomes. In all three groups, ribosomes are made of ribosomal RNA (rRNA) and protein, are not enclosed by a membrane, and synthesize proteins according to the sequence of messenger RNA (mRNA). Which claim is best supported by these observations?
Answer and reasoning
AEach group evolved ribosomes on its own because all cells need to make proteins. A student who thinks structures arise because organisms need them picks this. Need does not produce structures, and the shared composition and function of ribosomes in every group are better explained by common ancestry.
BEukaryotes descended from present-day bacteria, which passed ribosomes to them. A student who thinks one living group is the ancestor of another picks this. Present-day bacteria and eukaryotes are both descendants of shared ancestors; neither living group is the ancestor of the other.
CThe three groups descended from a common ancestor whose cells had ribosomes.Correct A structure with the same composition and function in every group of living things is best explained by inheritance from a common ancestor that already had it; ribosomes reflect the common ancestry of all known life.
DThe ribosomes of each group became alike through being used in the same way in all cells. A student who thinks use changes structures and that such changes are inherited picks this. Using a structure does not change the genes passed on; the similarity reflects shared ancestry.
Cells of a hypothetical mammal that secrete digestive proteins were given radioactively labeled amino acids for 3 minutes and then given only unlabeled amino acids. The graph shows the percentage of the labeled protein found in the rough ER, the Golgi complex and secretory vesicles at different times after labeling began. Which conclusion is best supported by the data?
Answer and reasoning
AThe labeled proteins were made in the Golgi complex and then moved into the rough ER. A student who thinks the Golgi complex makes proteins picks this. The graph shows the label in the rough ER first, when the Golgi complex holds only 8%.
BThe labeled proteins moved from the rough ER to the Golgi complex and then into secretory vesicles.Correct The label is highest in the rough ER first (86% at 5 min), peaks in the Golgi complex next (45% at 20 min), and rises in secretory vesicles last (82% at 90 min). As the label falls in one compartment it rises in the next, so the proteins moved along this path.
CThe labeled proteins were broken down in the rough ER, as the label there fell after 5 minutes. A student who reads a fall in label as breakdown picks this. The label lost from the rough ER reappears in the Golgi complex and then in secretory vesicles, so the proteins moved rather than being broken down.
DThe labeled proteins reached all three compartments at once by diffusing through the cytosol. A student who thinks proteins reach organelles by diffusing through the cytosol picks this. The three compartments reach their highest label at different times, in order, as expected for transport in vesicles.
The diagram shows part of a cell from a hypothetical animal, with four structures labeled W, X, Y and Z. In which labeled structure are proteins that will be secreted from the cell synthesized?
Answer and reasoning
AStructure X A student who thinks all ER makes proteins picks this. X is smooth ER, with no ribosomes on its membrane; its functions include detoxification and lipid synthesis.
BStructure Y A student who thinks the Golgi complex makes proteins picks this. Y, the stack of flattened sacs, is the Golgi complex, which modifies and packages proteins made on the rough ER.
CStructure WCorrect W is rough ER: membrane sheets with ribosomes (dots) on their surface. Rough ER helps carry out protein synthesis, including the synthesis of proteins that are secreted.
DStructure Z A student who thinks proteins are made in the nucleus picks this. Z, surrounded by a double membrane, is the nucleus, which holds the DNA; proteins are synthesized by ribosomes outside it.
Smooth ER carries out detoxification. Cultured cells of a hypothetical animal were exposed to a toxic compound for 1, 3 or 5 days, and the volume of smooth ER was measured in each group and in unexposed control cells. The graph shows the mean smooth ER volume as a percentage of cell volume (n = 20 cells per group), with error bars representing ±2 SE of the mean. Which statement is best supported by the data?
Answer and reasoning
AMean smooth ER volume was significantly greater than the control on each day of exposure. A student who treats any difference between means as significant picks this. The day 1 mean (9.0) is higher than the control (8.0), but the error bars overlap, so the difference on day 1 has not been shown to be significant.
BOn day 1, mean smooth ER volume in the exposed cells was the same as in the control cells. A student who reads overlapping error bars as showing equal means picks this. The means were 9.0 and 8.0; overlap means only that a difference was not shown.
COn day 5, every exposed cell had a larger smooth ER volume than every single one of the control cells. A student who thinks error bars show the range of individual values picks this. The bars show ±2 SE of the mean; individual cells can lie outside them, so the data do not show that every exposed cell exceeded every control cell.
DMean smooth ER volume differed significantly from the control on days 3 and 5 but not on day 1.Correct The ±2 SE bars for days 3 and 5 do not overlap the control bar, so those increases are likely significant. The day 1 bar overlaps the control bar, so no significant difference was shown on day 1.
Working No test statistic is calculated; the decision rests on the ±2 SE error bars. Control: mean 8.0, bar 6.8–9.2. Day 1: 9.0, bar 7.6–10.4, which overlaps the control bar (7.6–9.2), so no significant difference is shown. Day 3: 13.0, bar 11.5–14.5, which does not overlap the control bar (11.5 > 9.2), so the difference is likely significant. Day 5: 18.0, bar 16.2–19.8, no overlap with the control, likely significant. Overlap on day 1 does not show that the means are equal (9.0 vs 8.0), and SE bars describe the mean, not the range of individual cells.
Compound X prevents the Golgi complex from adding sugar chains to proteins. A student tests whether the sugar chains added in the Golgi complex are needed for the activity of an enzyme secreted by cultured cells of a hypothetical animal. Compound X is dissolved in a solvent. She sets up the four dishes shown in the table under identical conditions and later measures the activity of the enzyme in the medium of each dish. To test her idea, the result for dish 1 should be compared with the result for which dish?
Answer and reasoning
ADish 3, which has no cells, so no enzyme is secreted at all A student who thinks the best control contains nothing picks this. Dish 3 differs from dish 1 in having no cells, so it cannot show whether blocking the sugar chains changes the enzyme's activity.
BDish 4, which was given the same treatment as dish 1 A student who thinks the control should receive the same treatment picks this. Dish 4 is a repeat of dish 1; it cannot show what happens to the enzyme when sugar chains are added normally.
CDish 2, which differs from dish 1 only in lacking compound XCorrect Dish 2 has cells and the same solvent but no compound X, so the only difference from dish 1 is whether sugar chains can be added in the Golgi. Any difference in enzyme activity can be attributed to that.
DNo other dish, as dish 1's enzyme activity alone shows the effect A student who thinks one result is enough to test a claim picks this. Without dish 2, there is no measure of the enzyme's activity when the Golgi complex adds sugar chains normally.
A cell of a hypothetical animal secretes a protein hormone. In a variant of this cell, the Golgi complex cannot package proteins into vesicles, but the rough ER and Golgi complex otherwise function normally. Which prediction about the hormone in the variant cell is best supported?
Answer and reasoning
AThe hormone will accumulate in the Golgi complex instead of being secreted from the cell.Correct The hormone is made on the rough ER and delivered to the Golgi complex, which normally packages it into vesicles that carry it to the plasma membrane. If packaging fails, the hormone is expected to build up in the Golgi complex and not be secreted.
BThe hormone will diffuse out of the Golgi complex through the cytosol and still be secreted. A student who thinks proteins move through the cytosol by diffusion picks this. Secretory proteins are carried inside vesicles; without packaging, the hormone has no route to the plasma membrane.
CThe cell will stop making the hormone, since the Golgi complex is where proteins are made. A student who thinks the Golgi complex makes proteins picks this. The hormone is synthesized by ribosomes on the rough ER, which works normally, so it is still made.
DThe rough ER will package the hormone into vesicles for secretion in place of the Golgi. A student who thinks the ER packages proteins for secretion picks this. Vesicles from the ER carry proteins to the Golgi complex; it is the Golgi complex that packages proteins for their final destinations.
Which statement best explains how the structure of a mitochondrion's inner membrane allows ATP to be synthesized efficiently?
Answer and reasoning
AIts many folds form pockets that store ATP until the rest of the cell needs it. A student who thinks the folds store ATP picks this. The folds increase the surface area on which ATP is made; ATP is used continually rather than stored in the folds.
BIts folds give a large surface area for membrane-bound steps that make ATP.Correct The inner membrane is highly convoluted. Its folds increase its surface area, so more of the membrane-bound steps of ATP synthesis can take place at once, enabling ATP to be synthesized more efficiently.
CIt is smooth, so ATP can pass quickly out through the folded outer membrane. A student who thinks the outer membrane is the folded one picks this. The inner membrane is the folded one; the outer membrane is smooth.
DIts many folds give room to create the energy that is then stored in ATP. A student who thinks mitochondria create energy picks this. Energy is not created; it is transferred from food molecules to ATP, and the folds increase the surface area where this happens.
A particular lipid is normally broken down by one of the hydrolytic enzymes of lysosomes. Cells of a hypothetical animal lack this enzyme, and no other enzyme in their lysosomes can break down the lipid. Which prediction about these cells is best supported?
Answer and reasoning
AThe cells will stop delivering the lipid to their lysosomes, since they cannot digest it. A student who explains cell activity by need picks this. Cells do not stop a process because its purpose cannot be met; delivery continues and the lipid accumulates.
BMitochondria will take in the lipid and break it down instead, releasing its energy. A student who thinks mitochondria digest material taken into the cell picks this. Digestion of this lipid takes place in lysosomes; mitochondria do not take over that role.
CThe lipid will accumulate in the lysosomes, where nothing can hydrolyze it.Correct Delivery of the lipid to lysosomes continues, but without the hydrolytic enzyme that digests it, it is not broken down, so it is expected to accumulate inside the lysosomes.
DThe lipid will build up in the cytosol, where lysosomal enzymes normally digest it. A student who thinks lysosomal enzymes digest material in the cytosol picks this, expecting undigested lipid to collect there. Material delivered to lysosomes is digested inside them, so when the enzyme is missing the lipid accumulates inside the lysosomes.
In plant cells, a large central vacuole stores water and maintains turgor pressure. Researchers measured the mean vacuole volume in leaf cells of a hypothetical plant under the conditions shown in the table. By what percentage did the mean vacuole volume decrease after 3 days without water, compared with the well-watered plant?
Answer and reasoning
A55% A student who gives the new value as a percentage of the original picks this: 22/40 × 100 = 55%, the percentage of the original volume that remains.
B45%Correct The mean volume fell from 40 to 22 (× 10³ μm³), a change of 18. Percent decrease = 18/40 × 100 = 45%.
C18% A student who reports the difference as the percent change picks this. The difference, 18 × 10³ μm³, must be divided by the original volume, 40 × 10³ μm³.
D82% A student who divides the change by the new value picks this: 18/22 × 100 = 82%. Percent change is calculated relative to the original value.
Working From the table: well watered 40 × 10³ μm³; after 3 days without water 22 × 10³ μm³. Percent change = (new − original)/original × 100 = (22 − 40)/40 × 100 = −45%, a 45% decrease. Distractors: new as a percentage of the original, 22/40 × 100 = 55%; the difference reported as a percentage, 40 − 22 = 18 → 18%; the change divided by the new value, 18/22 × 100 = 82%.
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
