DP Biology (first assessment 2025)

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Question EXEX.1B.HL.TZ0.1

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Date Example questions Example questions Marks available [Maximum mark: 9] Reference code EXEX.1B.HL.TZ0.1
Level HL Paper 1B Time zone TZ0
Command term Calculate, Discuss, Identify, List, Suggest Question number 1 Adapted from N/A
1.
[Maximum mark: 9]
EXEX.1B.HL.TZ0.1

The cryo-electron micrograph shows viral particles of the genus Mimivirus.

[Source: Schrad, J.R.; Young, E.J.; Abrahão, J.S.; Cortines, J.R.; Parent, K.N. Microscopic Characterization of the Brazilian Giant Samba Virus. Viruses 2017, 9, 30. https://doi.org/10.3390/v9020030]

(a.i)

Identify the structure labelled X

[1]

Markscheme

capsid/ protein coat/ envelop;

(a.ii)

Use the scale bar to calculate the magnification of the image.

[1]

Markscheme

100 000 X;

 

Accept values between 90 000 and 110 000 X.

(a.iii)

From the electron micrograph, suggest which viral particle P or Q is likely to have already infected a host cell.

[1]

Markscheme

viral particle Q
AND
has no contents/genetic material (as it has been inserted in the host cell)  

OR  
the capsid/ envelope/protein coat is open/cut showing that its contents have been inserted into the host (cell);  

(b)

The fibres seen on the surface are a distinctive feature of this virus. List two other differences in structure that may occur between viruses.

[2]

Markscheme
  1. presence of envelope;
  2. genetic material can be DNA or RNA;
  3. presence of enzymes;
  4. different shapes/ rounded or elongated shapes;
(c)

Discuss the evidence provided by viral structure and function that suggests they evolved from living organisms.   

[4]

Markscheme
  1. complexity in structure/ big size of some viruses evidence evolution from bacteria that lost cell components/functions;
  2. e.g. they might have evolved from a kind of parasitic bacteria that can only replicate inside a host;
  3. retroviruses/ some viruses and some eukaryotic cells have similar mechanisms for the synthesis of DNA from RNA/ contain reverse transcriptases;
  4. suggesting genetic material moved out of cells and evolved into viruses;
  5. they are obligate parasites/, so they could not exist before living cells;
  6. all living organisms share same genetic material from universal common ancestor/LUCA, so viruses having similar genetic material must have evolved from cells;

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