AQA A-level Biology · 3.2

Cells

50 revision questions with answers for 3.2 Cells in AQA A-level Biology (spec 7402). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 3.2.1.1, 3.2.1.2 · Cell types · Recall
What is the central distinction between eukaryotic and prokaryotic cells?
Answer:
Eukaryotic cells have a nucleus and membrane-bound organelles. Prokaryotic cells lack these and are generally smaller. Both have a cell-surface membrane, cytoplasm, DNA and ribosomes.
Question 2 · Spec 3.2.1.1 · Nucleus · Application
How do the structures within a nucleus relate to its functions?
Answer:
The nuclear envelope separates nuclear contents from cytoplasm, with pores controlling exchange. Chromosomes contain linear DNA associated with proteins. The nucleolus produces ribosomal components. The nucleus stores genetic information and supports control of protein synthesis.
Question 3 · Spec 3.2.1.1 · Energy-related organelles · Recall
Compare mitochondria and chloroplasts.
Answer:
Mitochondria carry out aerobic respiration, with an inner membrane folded into cristae and a matrix containing enzymes. Chloroplasts carry out photosynthesis, with chlorophyll-containing thylakoids and a stroma. Both have a double envelope, DNA and ribosomes.
Question 4 · Spec 3.2.1.1 · Protein production · Application
How do ribosomes and rough endoplasmic reticulum contribute to protein production?
Answer:
Ribosomes translate mRNA to form polypeptides. Ribosomes attached to rough endoplasmic reticulum produce proteins that enter its membrane system for processing and transport, including proteins destined for secretion or membranes.
Question 5 · Spec 3.2.1.1 · Processing and secretion · Recall
What are the functions of smooth ER, Golgi apparatus and Golgi vesicles?
Answer:
Smooth ER synthesises and processes lipids. The Golgi modifies and packages proteins and lipids. Golgi vesicles transport these products to other cellular locations or to the cell-surface membrane for secretion.
Question 6 · Spec 3.2.1.1 · Lysosomes · Application
What are lysosomes and why are their enzymes enclosed by a membrane?
Answer:
Lysosomes contain hydrolytic enzymes that digest material such as engulfed pathogens and worn organelles. Their membrane compartmentalises these enzymes, controlling where digestion occurs and protecting other cell components.
Question 7 · Spec 3.2.1.1 · Walls and vacuoles · Application
How do cell walls and a plant cell vacuole support cells?
Answer:
Cell walls provide strength and support in plants, algae and fungi. A plant vacuole contains cell sap and is bounded by the tonoplast. Water entering the vacuole creates turgor pressure against the wall, helping support the tissue.
Question 8 · Spec 3.2.1.1 · Organisation · Recall
How are specialised cells organised in a multicellular organism?
Answer:
Specialised cells have structures suited to their functions. Groups of cells form tissues, different tissues form organs, and organs work together in organ systems. For example, cardiac muscle tissue contributes to the heart in the circulatory system.
Question 9 · Spec 3.2.1.2 · Prokaryotic structures · Recall
Which features help identify a prokaryotic cell in an image?
Answer:
Look for a small cell without a nucleus or membrane-bound organelles, smaller ribosomes, free circular DNA and a murein-containing wall. Some also have plasmids, a capsule or flagella. These additional structures are not present in every prokaryote.
Question 10 · Spec 3.2.1.2 · Virus structure · Recall
Why are viruses described as acellular, and what structures do they contain?
Answer:
Viruses lack cellular organisation and independent metabolism. A virus particle contains genetic material enclosed by a protein capsid and attachment proteins that bind to host cells. Some viruses also have a lipid envelope.
Question 11 · Spec 3.2.1.3 · Microscopes · Recall
Compare optical, transmission electron and scanning electron microscopes.
Answer:
Optical microscopes can examine living specimens but have lower resolution. TEM passes electrons through thin sections to show internal ultrastructure. SEM scans surfaces to give a three-dimensional appearance. Electron microscopy requires prepared specimens and cannot observe living cells.
Question 12 · Spec 3.2.1.3 · Resolution · Recall
Distinguish magnification from resolution.
Answer:
Magnification is image size divided by actual object size. Resolution is the ability to distinguish two close points as separate. Increasing magnification without improving resolution enlarges an image without revealing additional detail.
Question 13 · Spec 3.2.1.3, MS 1.8 · Microscopy calculation · Calculation
A cell image is 42 mm long at x1400 magnification. What is its actual length?
Answer:
Actual length = image length/magnification = 42/1400 = 0.030 mm. Multiplying by 1000 gives 30 micrometres. Convert image and actual lengths to the same units when calculating magnification.
Question 14 · Spec 3.2.1.3 · Eyepiece graticule · Practical
How is an eyepiece graticule calibrated and used?
Answer:
Align it with a stage micrometer. Calculate the actual distance represented by one graticule division, then multiply by the divisions occupied by the specimen. Recalibrate for each objective lens because the scale changes with magnification.
Question 15 · Spec 3.2.1.3 · Cell fractionation · Practical
Why is tissue homogenised in a cold, isotonic, buffered solution and then filtered?
Answer:
Homogenisation breaks cells open. Cold conditions reduce enzyme activity and organelle damage. An isotonic solution limits osmotic swelling or shrinking. A buffer maintains pH. Filtering removes large debris before centrifugation.
Question 16 · Spec 3.2.1.3 · Ultracentrifugati on · Practical
How are organelles separated by differential centrifugation?
Answer:
Centrifuge the homogenate at low speed to sediment larger, denser components such as nuclei. Remove the supernatant and centrifuge it at progressively higher speeds to sediment smaller components. Each pellet is enriched in particular organelles, but may contain contaminants.
Question 17 · Spec 3.2.2 · Cell cycle · Recall
What happens during interphase before mitosis?
Answer:
The cell grows and synthesises components. DNA replicates, producing two sister chromatids for each chromosome. Organelles and proteins needed for division are produced. The replicated DNA must be separated accurately during mitosis.
Question 18 · Spec 3.2.2 · Early mitosis · Recall
What distinguishes prophase and metaphase?
Answer:
During prophase, chromosomes condense, the nuclear envelope breaks down and a spindle forms. At metaphase, chromosomes align at the equator with spindle fibres attached at their centromeres, ready for sister chromatids to separate.
Question 19 · Spec 3.2.2 · Late mitosis · Recall
What happens during anaphase, telophase and cytokinesis?
Answer:
At anaphase, centromeres divide and sister chromatids move to opposite poles along spindle fibres. At telophase, chromosomes decondense and nuclear envelopes reform. Cytokinesis divides the cytoplasm, usually producing two genetically identical daughter cells.
Question 20 · Spec 3.2.2 · Other replication processes · Recall
How do binary fission and viral replication differ from mitosis?
Answer:
In binary fission, circular DNA and plasmids replicate before the cytoplasm divides. Each daughter receives a circular chromosome and may receive different plasmid numbers. Viruses use host-cell machinery to replicate their nucleic acid and make new particles.
Question 21 · Spec 3.2.2 · Cell division and cancer · Application
How can changes in the control of mitosis cause cancer, and why do some treatments affect healthy tissue?
Answer:
Loss of normal division control can produce a tumour. Treatments that inhibit DNA replication or spindle function reduce cell division. They can also affect healthy tissues containing rapidly dividing cells, producing side effects.
Question 22 · Spec 3.2.2, RP2 · Required practical 2 · Practical
Why use a stained root-tip squash to observe mitosis?
Answer:
Root tips contain many dividing meristem cells. Softening the tissue helps cells separate. Staining makes chromosomes visible, and squashing produces a thin layer with less overlap. Lower the coverslip carefully and press vertically to reduce chromosome distortion.
Question 23 · Spec 3.2.2, RP2, MS 0.3 · Required practical 2 · Calculation
In a root-tip sample, 36 of 240 cells are undergoing mitosis. Calculate the mitotic index.
Answer:
Mitotic index = cells in mitosis/total cells = 36/240 = 0.15, or 15%. Count several representative fields. If the cell-cycle duration is known, the proportion in a stage can estimate time spent in that stage, assuming a steady population.
Question 24 · Spec 3.2.3 · Fluid-mosaic model · Recall
Describe the arrangement and movement of molecules in a cell membrane.
Answer:
Phospholipids form a bilayer with hydrophilic heads facing water. Proteins are embedded within or attached to it. Glycoproteins and glycolipids carry carbohydrate groups. Many lipids and proteins move laterally, giving the membrane a fluid, mosaic structure.
Question 25 · Spec 3.2.3 · Cholesterol · Application
How does cholesterol influence membrane properties?
Answer:
Cholesterol fits between phospholipids and restricts their movement. It stabilises membranes and affects permeability. Its influence on fluidity depends on temperature, helping limit excessive movement at higher temperatures and close packing at lower temperatures.
Question 26 · Spec 3.2.3 · Simple diffusion · Recall
Which substances cross the phospholipid bilayer readily, and what determines diffusion rate?
Answer:
Small non-polar molecules, including oxygen and carbon dioxide, cross readily. Ions and many polar molecules cross poorly. A steeper concentration gradient, larger surface area and shorter diffusion distance increase net diffusion rate.
Question 27 · Spec 3.2.3 · Facilitated diffusion · Recall
How does facilitated diffusion differ from simple diffusion?
Answer:
Both are passive net movement down a concentration gradient. Facilitated diffusion uses specific channel or carrier proteins. Channels provide hydrophilic pathways for suitable particles. Carriers change shape when a suitable molecule binds. ATP is not directly required.
Question 28 · Spec 3.2.3 · Osmosis · Application
Define osmosis using water potential and predict what happens to a plant cell in a lower-water-potential solution.
Answer:
Osmosis is net water movement through a partially permeable membrane from higher to lower water potential. In a lower-water-potential external solution, the cell loses water, becomes flaccid and may plasmolyse as the protoplast pulls away from the wall.
Question 29 · Spec 3.2.3 · Active transport · Recall
How does active transport move a solute against its concentration gradient?
Answer:
The solute binds to a specific carrier protein. ATP hydrolysis supplies energy for a change in carrier shape, transporting the solute across the membrane. The carrier returns to its original state and can repeat the process.
Question 30 · Spec 3.2.3 · Sodium-glucose co-transport · Application
Explain how sodium ions enable glucose uptake into an ileum epithelial cell.
Answer:
The sodium-potassium pump uses ATP to move sodium out into the blood, keeping intracellular sodium low. Sodium enters from the gut lumen down its gradient through a co-transporter, carrying glucose with it against glucose's gradient. Glucose leaves towards the blood by facilitated diffusion.
Question 31 · Spec 3.2.3 · Transport adaptations · Application
How can cells increase the rate of transport across membranes?
Answer:
Microvilli or folded membranes increase surface area. More channels or carriers increase transport capacity for suitable substances. Many mitochondria can supply ATP for active transport. Maintaining concentration or water-potential gradients sustains net movement.
Question 32 · Spec 3.2.3, RP3, MS 2.3 · Required practical 3 · Calculation
How would you prepare 10 cm³ of 0.20 mol dm⁻³ sucrose from a 1.0 mol dm⁻³ stock?
Answer:
Use C1V1 = C2V2. V1 = (0.20 x 10)/1.0 = 2.0 cm³ of stock. Add water to a final volume of 10 cm³. Prepare a suitable series of known concentrations using the same method.
Question 33 · Spec 3.2.3, RP3 · Required practical 3 · Practical
How can plant tissue be used to investigate water potential?
Answer:
Cut similar tissue pieces, blot consistently and measure initial mass. Immerse in equal volumes of known sucrose concentrations for the same time and temperature. Blot and reweigh. Calculate percentage mass change and repeat to obtain means.
Question 34 · Spec 3.2.3, RP3 · Required practical 3 · Analysis
How is tissue water potential identified from a calibration curve?
Answer:
Plot mean percentage mass change against solution concentration or known solution water potential. The zero-mass-change intercept indicates no net osmosis. At this point, tissue and solution water potentials are equal. Use supplied concentration-water-potential data if needed.
Question 35 · Spec 3.2.3, RP4 · Required practical 4 · Practical
How can temperature effects on membrane permeability be investigated using beetroot?
Answer:
Use equal beetroot pieces, rinse away pigment released during cutting and place in equal water volumes at different temperatures for equal times. Measure released pigment with a colorimeter after removing the pieces. Greater absorbance indicates greater pigment leakage.
Question 36 · Spec 3.2.3, RP4 · Required practical 4 · Analysis
What controls and explanations are needed when interpreting beetroot permeability results?
Answer:
Control piece size, tissue source, rinsing, exposure time and solution volume. Use a blank to zero the colorimeter and repeat measurements. Higher temperature increases membrane disruption and may denature membrane proteins, allowing more pigment to escape.
Question 37 · Spec 3.2.4 · Antigens · Recall
What is an antigen, and why does antigen variation matter?
Answer:
An antigen is a molecule recognised as foreign that can trigger an immune response. Surface molecules help distinguish pathogens, foreign cells and abnormal cells. If a pathogen's antigens change, existing antibodies and memory cells may recognise it less effectively.
Question 38 · Spec 3.2.4 · Phagocytosis · Recall
How does a phagocyte destroy a pathogen?
Answer:
It recognises and engulfs the pathogen into a vesicle. Lysosomes fuse with the vesicle and release hydrolytic enzymes, including lysozyme, that digest the pathogen. Some phagocytes present pathogen antigens on their surface to activate a specific response.
Question 39 · Spec 3.2.4 · Cellular response · Recall
How are helper T cells involved in the cellular immune response?
Answer:
A helper T cell with a complementary receptor recognises antigen presented by an antigen-presenting cell. It becomes activated and divides. Helper T cells stimulate cytotoxic T cells, B cells and phagocytes. Cytotoxic T cells destroy infected body cells.
Question 40 · Spec 3.2.4 · Humoral response · Recall
Explain clonal selection of B cells.
Answer:
An antigen binds to a complementary B-cell receptor. With helper T-cell stimulation, the selected B cell divides by mitosis. Its clone differentiates into plasma cells that secrete antibodies of the same specificity and memory cells that support future responses.
Question 41 · Spec 3.2.4 · Antibody structure · Recall
How does an antibody's structure enable specific binding?
Answer:
An antibody has two heavy and two light polypeptide chains linked by disulfide bridges. Variable regions form two antigen-binding sites with a shape complementary to a particular antigen. The constant region can interact with immune-system components.
Question 42 · Spec 3.2.4 · Antibody action · Application
How do antibodies help remove bacterial cells?
Answer:
Their binding sites form antigen-antibody complexes. Because antibodies have two binding sites, they can cross-link bacteria into clumps, causing agglutination. Antibody-coated bacteria are more readily recognised and engulfed by phagocytes.
Question 43 · Spec 3.2.4 · Immune memory · Application
Why is a secondary immune response usually faster and larger than a primary response?
Answer:
Memory cells remain after the primary response. On re-exposure to the same antigen, specific memory cells divide rapidly and form many plasma cells. Antibody concentration rises sooner and often reaches a higher level, reducing disease symptoms.
Question 44 · Spec 3.2.4 · Vaccination · Recall
How do vaccines protect individuals and contribute to herd immunity?
Answer:
Vaccines introduce antigens in a form that stimulates an immune response without causing the target disease. Memory cells form. If enough people are immune, transmission falls, reducing exposure of susceptible individuals. Coverage required depends on the pathogen's transmissibility.
Question 45 · Spec 3.2.4 · Types of immunity · Recall
Distinguish active and passive immunity.
Answer:
Active immunity follows an individual's own response to an antigen and produces memory cells, for example after vaccination. Passive immunity results from receiving antibodies, for example across the placenta. Protection is immediate but temporary because those antibodies are broken down and memory cells are not generated.
Question 46 · Spec 3.2.4 · HIV structure · Recall
Which structural features of HIV are important in infection?
Answer:
HIV has attachment proteins on a lipid envelope, a protein capsid, RNA genetic material and reverse transcriptase. Attachment proteins bind to receptors on helper T cells. Reverse transcriptase enables a DNA copy of the viral RNA to be made.
Question 47 · Spec 3.2.4 · HIV and AIDS · Application
How does HIV replicate and lead to AIDS, and why do antibiotics fail to treat it?
Answer:
HIV enters helper T cells and reverse transcriptase makes viral DNA, which can integrate into host DNA. Host machinery produces viral components. Loss of helper T cells weakens immune responses and allows opportunistic infections. Antibiotics target bacterial structures or processes that viruses lack.
Question 48 · Spec 3.2.4 · Monoclonal antibodies · Application
How are monoclonal antibodies used in diagnosis and targeted treatment?
Answer:
They bind to one specific antigen. Diagnostic antibodies can detect a particular antigen in a sample. Antibodies linked to a therapeutic drug can bind target cells carrying the antigen, concentrating treatment at those cells. Effectiveness depends on antigen specificity and distribution.
Question 49 · Spec 3.2.4 · ELISA · Practical
Explain the principle of an ELISA test.
Answer:
A specific antibody or antigen is captured on a surface. An enzyme-linked antibody binds within the resulting complex. Washing removes unbound material. Adding the enzyme's substrate produces a colour if the target is present. Positive, negative and calibration controls support interpretation.
Question 50 · Spec 3.2.4 · Evaluating immune treatments · Analysis
What evidence and ethical factors should be considered when evaluating a vaccine or monoclonal-antibody treatment?
Answer:
Compare benefits and adverse effects using adequate sample sizes and appropriate controls. Consider disease severity, informed consent, access, cost and effects on vulnerable groups. Distinguish a reported event after treatment from evidence that the treatment caused it.

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