2025 AQA A-Level BIOLOGY 7402 3 Paper 3 Verified Question Paper and Marking Scheme Attached June 2025

A Level AQA Biology - [3.2] Cells
1. [Labelled diagram]
Explain why it is not possible to determine the identity of the structures labelled X using
an optical microscope.
[2 marks]
[3.1 - JUN21] [AS]: 1. Resolution (too) low;

2. Because wavelength of light is (too) long;
2. U. marinum cells ingest bacteria and digest them in the cytoplasm. Describe the role of
one named organelle in digesting these bacteria.
[3 marks]
[3.2 - JUN21] [AS]: 1. Lysosomes;


2. Fuse with vesicle;
Accept phagosome for vesicle

3. (Releases) hydrolytic enzymes;
Accept lysozymes for "hydrolytic enzymes"
3. Describe how a sample of chloroplasts could be isolated from leaves.
[4 marks]
[5.1 - JUN21]: 1. Break open cells/tissue and filter
OR
Grind/blend cells/tissue/leaves and filter;

2. In cold, same water potential/concentration, pH controlled solution; Accept isotonic, buffered
3. Centrifuge/spin and remove nuclei/cell debris;
4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out;
4. The figure below shows transmission electron micrographs of two cells, one animal cell [A] and one
prokaryotic cell [B].
Contrast the structure of the two cells.
[5 marks]
[4c PMT]: 1. Magnification (figures) show A is bigger than B;

2. A has a nucleus whereas B has free DNA;
3. A has mitochondria whereas B does not;
4. A has Golgi body/endoplasmic reticulum whereas B does not;
5. A has no cell wall whereas B has a murein/glycoprotein cell wall; Accept peptidoglycan
6. A has no capsule whereas B has a capsule;
7. A has DNA is bound to histones/proteins whereas B has DNA not associated with histones/proteins
OR
A has linear DNA whereas B has circular DNA;

8. A has larger ribosomes;



, A Level AQA Biology - [3.2] Cells
5. 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]
[4.1 - JUN20] [AS]: 1. DNA in nucleus is code (for protein);

2. Ribosomes/rough endoplasmic reticulum produce (protein);
3. Mitochondria produce ATP (for protein synthesis);
4. Golgi apparatus package/modify;
OR
Carbohydrate added/glycoprotein produced by Golgi apparatus; Accept body for 'apparatus'

5. Vesicles transport
OR
Rough endoplasmic reticulum transports;

6. (Vesicles) fuse with cell(-surface) membrane; Accept exocytosis at cell membrane 6. A scientist prepared a suspension
of organelles in a solution that prevented damage to the organelles.
Describe three properties of this solution and explain how each property prevented damage to the organelles.
[3 marks]
[5.6 - JUN19] [AS]: 1. (Ice) cold to prevent/reduce enzyme activity;

2. Buffered to prevent denaturing of enzyme/protein; Accept: prevent change of tertiary structure.
3. Same water potential/ ¨ to prevent lysis/bursting (of organelle);
Accept: isotonic for same water potential
7. Contrast how an optical microscope and a transmission electron microscope work and contrast the
limitations of their use when studying cells.
[6 marks]
[10.1 - JUN17]: 1. TEM use electrons and optical use light;

2. TEM allows a greater resolution;
3. (So with TEM) smaller organelles / named cell structure can be observed
OR
greater detail in organelles / named cell structure can be observed; 'clearer' is not equivalent to 'detail'

4. TEM view only dead / dehydrated specimens and optical (can) view live specimens;
Accept 'Only optical can view live specimens'

5. TEM does not show colour and optical (can); Accept 'Only optical can show colour'
6. TEM requires thinner specimens;
7. TEM requires a more complex/time consuming preparation;
Accept 'TEM requires a more difficult preparation'
Ignore references to artefacts