Pearson Edexcel International A Level Biology: Cell Ultrastructure and Microscopy (YBI11) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions follow the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology (YBI11) specification, Issue 2, statements 3.1 to 3.8 of Topic 3, including Core Practical 5. Topics 1 to 4 are International AS content, and there are no tiers. Read the study guide first and keep the revision notes beside you. The course hub, the checklist and the free diagnostics are linked for planning. Show all working in calculations.

Questions

1. (a) State two features that are common to all living cells. [2] (b) A student writes “the heart is a tissue.” Correct this statement by naming the level of organisation and two tissues found in the heart. [2]

2. Name the eukaryotic organelle described in each case. (a) A sac with a single membrane containing hydrolytic enzymes. [1] (b) The dense region inside the nucleus where ribosomal RNA is made. [1] (c) Two short hollow cylinders at right angles to each other, involved in forming the spindle. [1] (d) Tubular membranes with no ribosomes, involved in lipid synthesis. [1]

3. Cells from a gland were given radioactive amino acids for 2 minutes and then transferred to a medium with non-radioactive amino acids. The table shows where the radioactive protein was found, as a percentage of the total radioactive protein.

Time after the start (min)	rER	Golgi apparatus	Secretory vesicles	Outside the cell
2	90	8	2	0
10	52	34	13	1
20	18	28	44	10
40	6	8	30	56

(a) State the time at which the Golgi apparatus held the greatest percentage of radioactive protein. [1] (b) Describe the change in the percentage of radioactive protein in the rER. [2] (c) Explain why radioactive protein appeared in the Golgi apparatus before it appeared in secretory vesicles in large amounts. [2] (d) State how the protein leaves the cell. [1]

4. (a) State the function of each of these structures in a bacterial cell: the capsule, the plasmid and the pili. [3] (b) State two differences between the DNA of a bacterium and the DNA of a human liver cell. [2]

5. A transmission electron micrograph of a liver cell shows structure X, an oval about 1.5 micrometres long with a double boundary whose inner layer is folded inwards, and structure Y, a stack of flattened sacs with small round vesicles at one edge. (a) Identify X and Y, and state one function of each. [4] (b) The same type of organelle looks circular in one micrograph and long and thin in another. Explain why. [2]

6. A photomicrograph of a cell is 63 mm long. The real cell is 15 micrometres long. Calculate the magnification. [3]

7. An electron micrograph has a scale bar that is 30 mm long and represents 5 micrometres. (a) Work out the magnification of this micrograph. [2] (b) A vesicle measures 48 mm across on the micrograph. Calculate its real diameter in micrometres. [2]

8. (a) Distinguish between magnification and resolution. [2] (b) Explain why an electron microscope can show more detail than a light microscope. [2]

9. (a) Explain why a specimen of animal cells is stained before being viewed with a light microscope. [2] (b) State two reasons why living cells cannot be viewed in an electron microscope. [2]

10. A student calibrates an eyepiece graticule using a stage micrometer with divisions of 10 micrometres. At low power, 100 graticule divisions line up with 28 stage divisions. (a) Calculate the length in micrometres of one graticule division. [2] (b) A cell is 14 graticule divisions long. Calculate its length. [2] (c) The student changes to an objective lens that is four times as strong. State and explain the length of one graticule division now. [2] (d) The student draws the cell from (b) with a length of 98 mm. Calculate the magnification of the drawing. [1]

11. A student makes a labelled drawing of cheek cells seen with a light microscope. Describe four features of a good drawing. [4]

12. A transmission electron micrograph shows a pancreatic cell that secretes digestive enzymes. The scale bar is 20 mm long and represents 1 micrometre. A mitochondrion in the cell measures 24 mm long on the micrograph. The cell has extensive rER and many mitochondria. (a) Calculate the magnification of this image. [2] (b) Calculate the real length of the mitochondrion in micrometres. [2] (c) List, in order, the organelles and structures a digestive enzyme passes through from its synthesis to its release. [3] (d) Explain why this cell contains extensive rER and many mitochondria. [3]

Answers

1. (a) Any two from: cell surface membrane; DNA as genetic material; cytoplasm where metabolic reactions occur; ribosomes. One mark each: [1] [1]. [2] (b) The heart is an organ [1], made of tissues such as cardiac muscle and connective tissue (or epithelium) [1]. [2] Examiner insight: Naming the level and then two named tissues gives a complete correction; writing only “it is made of different cells” does not use the hierarchy the question asks for.

2. (a) Lysosome. [1] (b) Nucleolus. [1] (c) Centrioles. [1] (d) Smooth endoplasmic reticulum (sER). [1] [4] Examiner insight: Give the full name of the organelle; “ER” alone does not show whether you mean the rough or the smooth form.

3. (a) 10 minutes [1] (b) It falls [1] from 90% at 2 minutes to 6% at 40 minutes, with the fall being steepest early on (for example 90 to 52 between 2 and 10 minutes) [1]. [2] (c) The protein is made on the rER and then moves in vesicles to the Golgi apparatus [1], where it is modified and packaged into secretory vesicles, which takes more time [1]. [2] (d) By exocytosis, when secretory vesicles fuse with the cell surface membrane [1]. [1] Examiner insight: In a data question, quote figures from the table with their times; a description that only says “decreases” tends to gain less than one that includes values.

4. (a) Capsule: protects the cell or helps it stick to surfaces [1]. Plasmid: carries extra genes, for example antibiotic resistance [1]. Pili: attach to surfaces or other cells (some transfer DNA) [1]. [3] (b) Bacterial DNA is circular, human DNA is linear [1]. Bacterial DNA lies free in the cytoplasm, not in a nucleus enclosed by a nuclear envelope [1]. [2] Examiner insight: A comparison needs both sides stated. “Circular” on its own leaves the human cell unmentioned, so write each difference as a pair.

5. (a) X is a mitochondrion [1]; it makes ATP in aerobic respiration [1]. Y is a Golgi apparatus [1]; it modifies and packages proteins [1]. [4] (b) A micrograph shows a thin section [1], so the organelle is cut at different angles, giving a circle when cut across and a long shape when cut along its length [1]. [2] Examiner insight: For recognition questions, quote the identifying feature (double boundary with cristae folds, stack of sacs with vesicles) and then give the function; naming alone is rarely enough when the question asks for both.

6. Convert 63 mm to micrometres: 63 × 1000 = 63 000 [1]. Magnification = image ÷ real = 63 000 ÷ 15 [1]. ×4200 [1] [3] Examiner insight: If you divide 63 by 15 without converting units you get 4.2, a value that is clearly wrong for an electron or light micrograph; checking for sense is a quick safeguard.

7. (a) Bar length 30 mm = 30 000 micrometres; magnification = 30 000 ÷ 5 [1] = ×6000 [1] [2] (b) Real size = 48 ÷ 6000 mm [1] = 0.008 mm = 8.0 micrometres [1] [2] Examiner insight: Show the conversion step. An answer left in mm or in the wrong unit shows the method but is easy to lose the final result on.

8. (a) Magnification is the enlargement factor of the image compared with the object [1]; resolution is the least separation at which two points are still seen as two [1]. [2] (b) Electrons have a much shorter wavelength than light [1], so the electron microscope has a higher resolution and shows finer detail (ultrastructure) [1]. [2] Examiner insight: Link wavelength to resolution explicitly. A statement that an electron microscope “magnifies more” does not answer a question about detail.

9. (a) Cell structures are almost transparent, with little contrast [1]; a stain binds to particular structures and makes them visible [1]. [2] (b) Any two from: the specimen is in a vacuum; the specimen is cut as a thin section and treated with fixatives and heavy metal stains; the beam of electrons would damage the cells. One mark each: [1] [1]. [2] Examiner insight: Give two separate reasons. Repeating “they would die” twice in different words is one point.

10. (a) 28 stage divisions × 10 = 280 micrometres [1]; 280 ÷ 100 = 2.8 micrometres [1] [2] (b) 14 × 2.8 [1] = 39.2 micrometres [1] [2] (c) 0.7 micrometres [1], because the objective is four times as strong, so each division covers a quarter of the distance: 2.8 ÷ 4 [1] [2] (d) 98 mm = 98 000 micrometres; 98 000 ÷ 39.2 = ×2500 [1] [1] Examiner insight: Hold the unrounded value until the last line; using 39 in place of 39.2 would shift the final magnification to about 2513.

11. Any four from: drawn in pencil with clear, continuous lines; no shading or colouring; large drawing, with only a few cells drawn, showing the outline and structures seen; label lines drawn with a ruler and not crossing; label lines touching the structure; a title; the magnification, or a scale bar, included. One mark each: [1] [1] [1] [1]. [4] Examiner insight: Be specific about what you do. “Draw neatly” is too vague to gain credit, whereas “no shading” and “label lines do not cross” are checkable.

12. (a) 20 mm = 20 000 micrometres; magnification = 20 000 ÷ 1 [1] = ×20 000 [1] [2] (b) 24 ÷ 20 000 mm [1] = 0.0012 mm = 1.2 micrometres [1] [2] (c) Ribosomes on the rER (translation) [1]; transport vesicle to the Golgi apparatus, which modifies and packages the protein [1]; secretory vesicle that fuses with the cell surface membrane (exocytosis) [1]. [3] (d) The cell makes large quantities of protein, so it needs extensive rER to fold and process it [1]. Protein synthesis, vesicle movement and exocytosis all need ATP [1], so many mitochondria supply this by aerobic respiration [1]. [3] Examiner insight: Link each structure to a process: “extensive rER, so more protein made” gains credit where “it is a secretory cell” alone does not.

Where marks are usually lost

• Naming “ER” without saying rough or smooth.
• Stating that mitochondria “make energy” rather than ATP.
• Forgetting to convert millimetres to micrometres before dividing.
• Giving a magnification with a unit; it is written as a multiple such as ×4200.
• Writing that the Golgi apparatus makes proteins; ribosomes make them.
• Describing data without quoting figures from the table.
• Saying prokaryotes have no DNA, rather than circular DNA outside a nucleus.
• Drawings with shading, crossing label lines or no magnification.
• Using one graticule calibration for every objective lens.

Next steps

• Review the revision notes and the study guide.
• Visit the Edexcel A Level Biology hub and tick off topics on the checklist.
• Try all free 10-minute diagnostics at /diagnostics/.
• Book a free trial class.

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level in Biology (YBI11), Specification, Issue 2, Pearson Education Limited. Statements 3.1 to 3.8 of Topic 3.