Question 1
The row that correctly classifies the cell structure according to this syllabus is shown in which option?
A.
Cell wall — organelle — extracellular structure giving support and protection
B.
Ribosome — organelle — site of polypeptide synthesis from mRNA
C.
Cytoplasm — organelle — site containing the cell’s organelles and dissolved substances
D.
Cytoskeleton — organelle — network of protein filaments organizing the cell
Question 2
In differential centrifugation of a cell homogenate, larger or denser organelles are separated from smaller organelles mainly because they...
A.
bind more strongly to the buffer used during homogenization
B.
are broken into smaller fragments by the ultracentrifuge
C.
sediment into a pellet at lower speeds or shorter spin times
D.
move to the top of the tube because they are more soluble
Question 3
What advantage is provided by separating the nucleus from the cytoplasm in eukaryotic cells?
A.
Ribosomes can enter the nucleus to translate mRNA beside chromosomes
B.
Translation can occur before transcription has finished
C.
Post-transcriptional modification of mRNA can occur before translation
D.
DNA can leave the nucleus to act directly as a template for ribosomes
Question 4
What is an advantage of compartmentalizing enzymes and metabolites for a biochemical pathway inside an organelle?
A.
It increases their effective concentration and can increase reaction efficiency
B.
It removes the need for substrates in metabolic reactions
C.
It prevents every enzyme in the pathway from being affected by temperature
D.
It changes all metabolites into membrane proteins for transport
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Question 5
A student listed the following cell structures: nucleus, ribosome, plasma membrane, cytoplasm, cell wall and vesicle.
State two structures in the list that are considered organelles in this syllabus.
[2]
Distinguish between an organelle and the cytoplasm.
[2]
Question 6
A mutation causes a eukaryotic cell to export RNA transcripts from the nucleus immediately after transcription. What consequence is most directly related to loss of nuclear compartmentalization?
A.
Reduced opportunity to modify mRNA before ribosomes translate it
B.
Elimination of all ribosomes from the cytoplasm
C.
Complete prevention of transcription from using a DNA template
D.
Inability of amino acids to form peptide bonds in ribosomes
Question 7
A phagocytic cell engulfs a bacterium into a membrane-bound vacuole. Lysosomes then fuse with this vacuole. What benefit does this compartmentalization provide?
A.
The bacterium is translated into protein by ribosomes in the vacuole
B.
All cytoplasmic enzymes are released to digest the cell contents
C.
The vacuole becomes a nucleus that stores bacterial chromosomes
D.
Hydrolytic enzymes digest the bacterium in a controlled space
Question 8
A muscle cell has mitochondria with highly folded inner membranes. How does this adaptation support ATP production?
A.
Cristae store DNA so that transcription can occur outside the matrix
B.
Cristae increase surface area for electron transport proteins and ATP synthase
C.
Cristae reduce the number of membrane proteins needed for respiration
D.
Cristae form vesicles that carry ATP directly to ribosomes
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Question 9
What feature of chloroplast thylakoids helps a proton gradient develop rapidly during the light-dependent reactions?
A.
The presence of Calvin cycle enzymes inside the thylakoid membrane
B.
The large volume of stroma surrounding the thylakoids
C.
The absence of photosystems from thylakoid membranes
D.
The small volume of fluid inside each thylakoid
Question 10
A protein is synthesized by a free ribosome in the cytoplasm rather than by a ribosome bound to rough endoplasmic reticulum. The most likely destination of this protein is...
A.
insertion into the plasma membrane during synthesis in the ER lumen
B.
immediate secretion outside the cell by exocytosis from the rough ER
C.
retention in the cell, such as functioning in the cytoplasm
D.
digestion inside a lysosome before the polypeptide is completed
Question 11
A newly synthesized secretory protein leaves the rough endoplasmic reticulum in a vesicle. What is the next role of the Golgi apparatus in this pathway?
A.
Transcribing the gene for the protein from chromosomal DNA
B.
Processing the protein and packaging it into vesicles for secretion
C.
Hydrolysing the mRNA used to synthesize the protein
D.
Producing ATP to power peptide bond formation at ribosomes
Question 12
Cell fractionation can be used to isolate organelles from liver cells before testing their enzyme activity.
State why the cells are kept in a cold, buffered solution during fractionation.
[2]
Outline how differential centrifugation separates cell components.
[2]
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Question 13
The diagram compares gene expression in a eukaryotic cell and in a prokaryotic cell.
State the two processes separated by the nuclear envelope in eukaryotic cells.
[2]
Explain one advantage of this separation for eukaryotic cells.
[2]
Question 14
A metabolic pathway in a eukaryotic cell uses five enzymes and several small metabolites. The enzymes are located inside the same membrane-bound compartment.
Suggest two reasons why locating the enzymes and metabolites in the same compartment can increase the efficiency of the pathway.
[2]
State one other advantage of compartmentalization in the cytoplasm of cells.
[1]
Question 15
The nuclear envelope is a double membrane containing many nuclear pores. During nuclear division it can break down and later reform.
Outline why nuclear pores are needed in the nuclear envelope.
[2]
Outline one functional benefit of the nuclear envelope breaking into vesicles during mitosis or meiosis.
[2]
Question 16
A pancreatic cell produces digestive enzymes for secretion and also produces enzymes that remain in its cytoplasm.
State the destination of proteins synthesized by free ribosomes.
[1]
Contrast free ribosomes with ribosomes bound to rough endoplasmic reticulum in terms of protein destination.
[3]
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Question 17
A student used an electron microscope to examine structures in a eukaryotic cell. The table shows observations for six cell structures.
Structure | Observation in electron microscope | Position / relation in cell |
|---|---|---|
Cell wall | Thick, rigid outer layer with fibrous texture | Outside the plasma membrane |
Plasma membrane | Very thin, flexible, continuous layer; selectively permeable | Immediately inside the cell wall |
Cytoplasm | Semi-fluid granular material filling most of the cell; contains many structures | Inside the plasma membrane |
Nucleus | Large rounded body with a double membrane and pores | In the cytoplasm |
Mitochondrion | Oval body with folded inner membranes | In the cytoplasm |
Ribosome | Very small dark particles; not enclosed by a membrane | Free in the cytoplasm |
State the structure in the table that is an organelle but is not membrane-bound.
[1]
Using evidence from the table, distinguish between the cell wall and the plasma membrane as cell structures.
[2]
Suggest why cytoplasm is not classified as an organelle in this syllabus.
[1]
Question 18
An annotated transmission electron micrograph shows part of a plant cell. Four labelled regions are shown.
Identify one labelled structure that is an organelle because it is a discrete subunit adapted for a specific function.
[1]
State why the labelled cell wall is not considered an organelle in this syllabus.
[1]
Outline why the labelled ribosomes can be classified as organelles even though they are not surrounded by a membrane.
[1]
Question 19
During mitosis, the nuclear envelope breaks down and later reforms around separated chromosomes. What property of the nuclear envelope makes this possible?
A.
It is composed of ribosomes that disassemble during translation
B.
It is a double membrane that can break into vesicles and later fuse again
C.
It is a rigid extracellular wall that remains intact during chromosome movement
D.
It is a single layer of cytoskeletal filaments that contracts at the equator
Question 20
What is the role of clathrin during clathrin-mediated vesicle formation?
A.
It catalyses peptide bond formation on the rough endoplasmic reticulum
B.
It assembles into a coat that helps curve the membrane into a budding vesicle
C.
It hydrolyses proteins inside lysosomes after phagocytosis
D.
It forms nuclear pores for export of mRNA from the nucleus
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Question 21
A phagocytic white blood cell engulfs a bacterium into a membrane-bound vacuole. Lysosomes then fuse with the vacuole.
Identify the organelle that contains hydrolytic enzymes for digesting the bacterium.
[1]
Explain how compartmentalization allows digestion of the bacterium without widespread damage to the cell.
[3]
Question 22
In bacteria, mRNA may meet ribosomes almost immediately after it is transcribed. In eukaryotes, the transcript is made in the nucleus before entering the cytoplasm.
Compare the location of transcription and translation in prokaryotic and eukaryotic cells.
[2]
Suggest why immediate contact between mRNA and ribosomes is a disadvantage for mRNA processing.
[2]
Question 23
The diagram shows a mitochondrion from a cell with a high demand for ATP.
State the region of a mitochondrion where enzymes and substrates of the Krebs cycle are compartmentalized.
[1]
Explain two adaptations of the mitochondrion for ATP production by aerobic cell respiration.
[3]
Question 24
The chloroplast contains stacks of thylakoids surrounded by stroma.
Identify the compartment that contains enzymes and substrates of the Calvin cycle.
[1]
Explain how thylakoids are adapted for the light-dependent reactions of photosynthesis.
[3]
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Question 25
A protein synthesized on the rough endoplasmic reticulum is later released from the cell by exocytosis.
State the face of the Golgi apparatus from which secretory vesicles leave.
[1]
Explain the role of the Golgi apparatus in secretion of protein.
[3]
Question 26
Researchers compared the timing of transcription and translation for the same gene in a eukaryotic cell and a prokaryotic cell after the gene was activated.
Describe one difference between the timing of polypeptide production in the two cells.
[1]
Explain how the nucleus accounts for the pattern shown in the eukaryotic cell.
[2]
Suggest why the prokaryotic cell can begin polypeptide production before all mRNA from the gene has been completed.
[1]
Question 27
A macrophage engulfed bacteria into phagocytic vacuoles. The activity of a lysosomal hydrolase was measured at different pH values, and the pH inside the vacuole was measured before and after fusion with lysosomes.
Measurement | pH | Relative hydrolase activity / % |
|---|---|---|
Lysosomal hydrolase | 3.5 | 5 |
Lysosomal hydrolase | 4.0 | 20 |
Lysosomal hydrolase | 4.5 | 60 |
Lysosomal hydrolase | 4.8 | 90 |
Lysosomal hydrolase | 5.0 | 100 |
Lysosomal hydrolase | 5.2 | 90 |
Lysosomal hydrolase | 5.5 | 60 |
Lysosomal hydrolase | 6.0 | 25 |
Lysosomal hydrolase | 6.5 | 5 |
Phagocytic vacuole before fusion | 7.2 | — |
Phagocytic vacuole after fusion | 5.1 | — |
State the approximate pH at which the hydrolase has maximum activity.
[1]
Describe the change in pH of the phagocytic vacuole after fusion with lysosomes.
[1]
Explain how compartmentalization contributes to digestion of the engulfed bacteria.
[2]
Suggest one risk to the cell if the lysosomal enzymes were released freely into the cytoplasm.
[1]
Question 28
A model was used to compare a metabolic pathway when its enzymes and metabolites were either dispersed throughout the cytoplasm or held together inside a membrane-bound compartment.
Compare the rate of product formation in the two treatments during the first few minutes.
[1]
Explain the difference shown in the model.
[2]
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Question 29
Fluorescent labels were used to follow movement of molecules across the nuclear envelope in living cells. The cells were also observed during mitosis.
Labelled molecule/structure | Relative size | 0 min | 20 min | During mitosis |
|---|---|---|---|---|
mRNA | large | fluorescence mainly in nucleus | fluorescence mainly in cytoplasm | not shown |
tRNA | small | fluorescence mainly in nucleus | fluorescence mainly in cytoplasm | not shown |
Ribosomal subunit | very large | fluorescence mainly in nucleus | fluorescence mainly in cytoplasm | not shown |
Histone protein | large | fluorescence mainly in nucleus | fluorescence mainly in nucleus | not shown |
Nuclear envelope | double membrane | continuous nuclear outline | continuous nuclear outline | outline breaks into small membrane vesicles in prophase, then reappears around each chromosome set in telophase |
State the structure in the nuclear envelope that permits regulated movement of large molecules.
[1]
Using the data, identify one molecule or structure that must leave the nucleus for protein synthesis in the cytoplasm.
[1]
Explain why nuclear pores must be large and regulated rather than simple ion channels.
[1]
Suggest how the double membrane of the nuclear envelope is advantageous during mitosis.
[1]
Question 30
Pancreatic cells were pulse-labelled with a radioactive amino acid. At different times after labelling, the location of the radioactive protein was recorded.
State the order in which the labelled protein passes through cell compartments before secretion.
[1]
Identify the face of the Golgi apparatus that receives vesicles from the rough ER.
[1]
Explain the role of the Golgi apparatus in the secretion of the labelled protein.
[2]
Question 31
Receptor-mediated endocytosis involves the formation of vesicles at the plasma membrane. Clathrin is found on the cytoplasmic side of the membrane where the vesicle forms.
State the general structure of a vesicle.
[1]
Explain the role of clathrin in vesicle formation.
[3]
Question 32
Liver cells were homogenized in cold buffered solution. The homogenate was centrifuged repeatedly at increasing speeds. The activity of marker enzymes was measured in each pellet.
Identify the fraction most enriched in nuclei.
[1]
Explain why different organelles are found in different pellets during differential centrifugation.
[2]
Suggest why the homogenization was carried out in a cold buffered solution.
[1]
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Question 33
Mitochondria were isolated from two types of mammalian muscle fibre. Measurements of inner membrane surface area, intermembrane-space volume and ATP production were made under identical conditions.
Muscle fibre type | Inner membrane surface area / | Intermembrane-space volume / | ATP production / |
|---|---|---|---|
Fibre A | 0.38 | 16.2 | |
Fibre B | 0.71 | 8.7 |
Identify the mitochondrial feature most directly responsible for the larger inner membrane surface area.
[1]
Explain how the feature identified in part (a) can increase ATP production.
[2]
Suggest why a small intermembrane-space volume is an adaptation for aerobic respiration.
[1]
State where the enzymes and substrates of the Krebs cycle are compartmentalized in mitochondria.
[1]
Question 34
Chloroplasts were isolated from leaves grown in low light and high light. The organization of thylakoids and the rate of photosynthetic ATP production were compared.
State the chloroplast structure that contains photosystems for the light-dependent reactions.
[1]
Describe the relationship shown between thylakoid membrane surface area and photosynthetic ATP production.
[1]
Explain how grana can contribute to the relationship described in part (b).
[2]
Suggest why the small volume inside thylakoids is useful during ATP production.
[1]
Question 35
Cells were briefly supplied with radioactive amino acids. Newly synthesized proteins were then separated according to their final destination. The proportion made on free ribosomes and on ribosomes bound to rough endoplasmic reticulum was estimated.
Identify one protein type in the chart that is synthesized mainly by free ribosomes.
[1]
Contrast the usual destination of proteins synthesized by free ribosomes with proteins synthesized by ribosomes bound to rough ER.
[2]
Suggest why the secreted hormone is associated with rough ER rather than free ribosomes.
[1]
Question 36
Endocytosis of a receptor-bound protein was studied in cultured animal cells. Some cells were treated with a molecule that prevents clathrin assembly.
Describe the effect of preventing clathrin assembly on uptake of the fluorescent protein.
[1]
Explain the role of clathrin in vesicle formation.
[2]
Suggest one way in which vesicles formed by this process contribute to compartmentalization in cells.
[1]
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Question 37
A student classified several cell structures as organelles and proposed using cell fractionation to investigate their functions.
Evaluate the student's classification of cell structures as organelles.
I.
Explain why ribosomes, vesicles and the plasma membrane can be classified as organelles.
[2]
II.
Distinguish these organelles from the cell wall, cytoskeleton and cytoplasm.
[2]
Discuss how the development of ultracentrifugation and cell fractionation allowed scientists to investigate the functions of organelles.
[3]
Question 38
Macrophages engulf bacteria by phagocytosis. A phagocytic vacuole then fuses with lysosomes so that the bacteria are digested inside the cell.
Explain why lysosomes and phagocytic vacuoles are useful examples of compartmentalization.
I.
Explain the role of lysosomes in intracellular digestion.
[2]
II.
Explain the function of a phagocytic vacuole after a bacterium is engulfed.
[2]
Discuss two broader advantages of compartmentalization in the cytoplasm of cells.
[3]
Question 39
Some metabolic pathways in eukaryotic cells occur in small membrane-bound compartments rather than throughout the cytoplasm.
Discuss how compartmentalization affects the efficiency and control of metabolic reactions.
I.
Explain how concentrating enzymes and metabolites can affect a pathway.
[2]
II.
Explain how separate compartments allow different conditions to exist in the same cell.
[2]
Evaluate the importance of separating incompatible biochemical processes, using lysosomes as an example.
[3]
Question 40
A secretory cell contains many ribosomes in the cytoplasm and many ribosomes attached to rough endoplasmic reticulum.
Compare the structure and function of free ribosomes and ribosomes bound to rough endoplasmic reticulum.
I.
Outline two structural features shared by free and bound ribosomes.
[2]
II.
Contrast the usual destinations of proteins made by free ribosomes and bound ribosomes.
[3]
Explain how the structure of rough endoplasmic reticulum is related to its role in protein transport.
[3]
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Question 41
Eukaryotic cells contain a nucleus whereas prokaryotic cells do not. This affects the timing of gene expression.
Compare the locations of transcription and translation in eukaryotic and prokaryotic cells.
I.
Explain the location of transcription and translation in eukaryotic cells.
[2]
II.
Explain why transcription and translation can be closely coupled in prokaryotes.
[1]
Discuss the advantage to eukaryotic cells of separating transcription from translation.
[5]
Question 42
A biologist compared two cell types. Cell X contains many discrete structures visible in electron micrographs. Cell Y contains a cell wall, cytoplasm and a cytoskeletal network, but fewer membrane-bound compartments.
Evaluate the statement that all visible structures in a cell should be called organelles.
I.
Explain the criteria for classifying a structure as an organelle.
[2]
II.
Explain why visibility or size alone is not enough to classify a structure as an organelle.
[2]
Discuss how the concept of structure–function correlation applies to organelles, using two examples.
[4]
Question 43
A homogenate of eukaryotic cells was separated by differential centrifugation. The relative amount of protein and RNA in each pellet was then measured.
Pellet fraction | Centrifugation speed / g | Protein / a.u. | RNA / a.u. |
|---|---|---|---|
Pellet 1 | 1,000 | 84 | 5 |
Pellet 2 | 10,000 | 57 | 10 |
Pellet 3 | 30,000 | 36 | 18 |
Pellet 4 | 100,000 | 27 | 40 |
Analyse how differential centrifugation separates organelles from a homogenate.
I.
Explain why cells are placed in cold, buffered solution before homogenization.
[2]
II.
Explain why different pellets form at different centrifugation speeds.
[2]
Suggest how the fraction rich in ribosomes could be identified and used to investigate organelle function.
[4]
Question 44
Cells in flight muscle have a high demand for ATP and contain mitochondria with extensive internal membranes.
Explain how mitochondrial membranes are adapted for ATP production by aerobic cell respiration.
I.
Explain the importance of the small intermembrane space.
[2]
II.
Explain the significance of cristae in mitochondria of cells with high ATP demand.
[3]
Discuss the role of the mitochondrial matrix as a compartment in aerobic respiration.
[3]
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Question 45
The chloroplast is adapted for photosynthesis by an internal membrane system and separate fluid compartments.
Explain how the thylakoid system is adapted for the light-dependent reactions of photosynthesis.
I.
Explain the significance of the large surface area of thylakoid membranes.
[3]
II.
Explain the importance of the small volume of fluid inside thylakoids.
[2]
Discuss how the stroma contributes to photosynthesis as a compartment.
[3]
Question 46
The nuclear envelope must separate the nucleus from the cytoplasm, but it must also allow controlled exchange and reorganize during nuclear division.
Discuss functional benefits of the double membrane of the nucleus.
I.
Explain why nuclear pores are needed in the nuclear envelope.
[2]
II.
Explain how nuclear pores can exist in a double membrane.
[2]
Evaluate the advantage of the nuclear envelope breaking into vesicles during mitosis or meiosis.
[3]
Question 47
A pancreatic cell secretes digestive enzymes. Proteins synthesized on rough endoplasmic reticulum are delivered to the Golgi apparatus before secretion.
Explain the role of the Golgi apparatus in processing proteins for secretion.
I.
Describe how proteins enter and move through the Golgi apparatus.
[2]
II.
Explain how the structure of the Golgi apparatus allows protein processing.
[3]
Discuss how processed proteins are secreted from the cell after leaving the Golgi apparatus.
[3]
Question 48
Clathrin-mediated vesicle formation was inhibited in cultured cells. Researchers observed reduced uptake of some membrane proteins and reduced delivery of some cargo between compartments.
Explain how vesicles form and function as moving compartments in cells.
I.
Explain the role of clathrin in vesicle formation.
[3]
II.
Explain why vesicles are considered organelles adapted for transport.
[2]
Evaluate the likely effects of inhibiting clathrin-mediated vesicle formation on compartmentalized cell function.
[3]
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