AQA AS Level Biology Paper 1, November 2020: Question 4

9 marks · Medium difficulty · Short Answer

Outline the role of organelles in protein production and transport, suggest why a nucleus is not visible in a TEM micrograph, identify organelles S and T, give an advantage of TEM over SEM, and calculate the number of cells in a leaf surface in standard form.

Practise this question

Question

Question text

04.1 Eukaryotic cells produce and release proteins.

Outline the role of organelles in the production, transport and release of proteins from

eukaryotic cells.

Do not include details of transcription and translation in your answer.

[4 marks]

Figure 3 is a transmission electron micrograph of a plant cell.

Figure 3

04.2 Suggest why a nucleus is not visible in Figure 3.

[1 mark]

04.3 Name the organelles labelled S and T in Figure 3.

[1 mark]

Organelle S

Organelle T

04.4 Give one advantage of viewing a biological specimen using a transmission electron

microscope compared with using a scanning electron microscope.

[1 mark]

04.5 The cells in Figure 4 are part of a continuous layer of cells forming the upper surface

of a leaf.

The shaded area of cell U is 150 μm2

The total area of the upper surface of the leaf is 70.65 cm2

Figure 4

Calculate the number of cells in the upper surface of the leaf.

Give the answer in standard form.

Assume that all these cells are identical in size.

Show your working.

[2 marks]

Number of cells

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

04.1 4 max

1. DNA in nucleus is code (for protein);

2. and 5. Accept rER

2. Ribosomes/rough endoplasmic reticulum

for ‘rough

produce (protein);

endoplasmic

3. Mitochondria produce ATP (for protein reticulum’

synthesis);

4 Golgi apparatus package/modify; 4. Accept body for

‘apparatus’

Carbohydrate added/glycoprotein produced by

Golgi apparatus;

5 Vesicles transport

Rough endoplasmic reticulum transports;

6. (Vesicles) fuse with cell(-surface) membrane; 6. Accept exocytosis

at cell membrane

04.2 A section/slice (so nucleus in another part of cell) 1

(Nucleus) not stained;

04.3 1 Reject

thylakoid/granum

S = Vacuole

Reject incorrect

T = Chloroplast; spelling

04.4 Higher resolution 1

– LOGY – – JUNE 2020

View internal structures;

04.5 Correct answer of 4.71 x 107 for 2 marks;; 2

Accept for 1 mark

Any answer showing conversion factor of

100 000 000 / 108

Correct answer for any number divided by 150 eg

70.65 ÷ 150 / 0.471

Any answer including digits 471 in this order,

irrespective of position of decimal place

TOTAL 9

How to answer it

Eukaryotic Cells, Organelles, and Microscopy Study Guide

What this question tests

This assessment evaluates your understanding of eukaryotic ultrastructure, the precise functional roles of organelles in protein synthesis and transport, cell ultrastructure identification from electron micrographs, microscope capabilities (TEM vs SEM), and multi-step unit conversion calculations involving standard form.

Question 04.1

Protein Production and Organelle Roles

Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells (excluding transcription and translation). [4 marks]

✅ Correct Answer / Mark Scheme

DNA/Nucleus: Contains the genetic code for the protein.
Ribosomes / Rough Endoplasmic Reticulum (rER): Synthesise/produce the protein.
Mitochondria: Produce ATP required for protein synthesis and transport.
Golgi apparatus: Packages, modifies, and adds carbohydrates to proteins (forms glycoproteins).
Vesicles / rER: Transport the proteins through the cytoplasm.
Cell-surface membrane: (Vesicles) fuse with the membrane to release proteins via exocytosis.

💡 Key Knowledge

This is the classic "protein journey" through a eukaryotic cell. You must link the structural organelle directly to its precise dynamic function in secretory pathways.

🧠 Exam Technique

This is a "4 max" question. You need to write coherent, point-to-point statements connecting organelle to function. Do not waste time writing about transcription or translation, as the question explicitly forbids it.

❌ Common Errors

Students often lose marks by stating mitochondria "make energy" (violating the conservation of energy principle—they produce ATP) or by confusing the roles of vesicles and the Golgi apparatus.

Maximum 4 marks available. Any 4 valid points from the mark scheme.

Question 04.2

Missing Nucleus in Transmission Electron Micrograph

Suggest why a nucleus is not visible in Figure 3. [1 mark]

✅ Correct Answer

The cell was sectioned/sliced, so the nucleus is located in another part (another slice) of the cell, OR the nucleus was not stained.

🧠 Exam Technique

For 1-mark "suggest why" questions regarding 2D micrographs, always consider tissue preparation artifacts: thin sectioning means structures present in 3D might be entirely missed in a 2D plane.

1 mark available.

Question 04.3

Organelle Identification

Name the organelles labelled S and T in Figure 3. [1 mark]

✅ Correct Answers

Organelle S: Vacuole
Organelle T: Chloroplast

❌ Common Errors

Reject answers like "thylakoid" or "granum" for organelle T—these are internal structures within the chloroplast, not the organelle itself. Ensure correct biological spelling.

1 mark available for both correct identifications.

Question 04.4

Microscopy Comparison

Give one advantage of viewing a biological specimen using a transmission electron microscope (TEM) compared with using a scanning electron microscope (SEM). [1 mark]

✅ Correct Answer

Higher resolution OR ability to view internal structures (such as chloroplast grana or mitochondrial cristae).

💡 Key Knowledge

TEM transmits electrons through a very thin specimen, giving 2D internal details at a higher resolution than SEM, which bounces electrons off the surface to generate 3D topography images.

1 mark available.

Question 04.5

Multi-Step Calculation & Standard Form

Calculate the number of cells in the upper surface of the leaf. Give the answer in standard form. Assume that all these cells are identical in size. [2 marks]

📐 Step-by-Step Calculation

Convert units to match: Area of cell U = 150 um². Total area = 70.65 cm². Convert cm² to um².
1 cm = 10,000 um (10⁴ um).
1 cm² = (10⁴)² um² = 10⁸ um².
Calculate total leaf surface area in um²:
70.65 cm² × 10⁸ = 7,065,000,000 um² (or 7.065 × 10⁹ um²).
Divide total area by single cell area:
7,065,000,000 um² ÷ 150 um² = 47,100,000 cells.
Convert to standard form:
4.71 × 10⁷

❌ Common Calculation Traps

The most frequent error is squaring the conversion factor incorrectly. Remember that converting cm to um is multiplying by 10⁴, but converting cm² to um² requires multiplying by ( 10⁴ )² = 10⁸ !

2 marks available: 1 mark for correct conversion factor or division method, 2 marks for the final correct standard form answer ( 4.71 × 10⁷ ).

Topics

Biology · Practical skills · 3.2 Cells · Data analysis

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.