DP Biology (first assessment 2025)

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Question 19M.2.SL.TZ1.2a

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.SL.TZ1.2a
Level SL Paper 2 Time zone TZ1
Command term Distinguish Question number a Adapted from N/A
a.
[Maximum mark: 2]
19M.2.SL.TZ1.2a
(a)

Distinguish between the structure of the chromosomes of prokaryotes and eukaryotes.

[2]

Markscheme

a. prokaryotes have circular DNA/chromosome but eukaryote chromosomes linear/OWTTE ✔
OR
eukaryotes have telomeres/centromeres whereas prokaryotes do not ✔

b. some prokaryotes have plasmids whereas eukaryotes do not ✔

c. eukaryotes have multiple chromosomes whereas prokaryotes «typically» have only one ✔

d. histones/nucleosomes/proteins associated with DNA in eukaryotes but not in prokaryotes/naked DNA in prokaryotes
OR
eukaryote DNA can coil/supercoil/condense «due to histones» but not prokaryote DNA ✔

Examiners report

Answers to this question were variable. Some candidates wrote about cell structure rather than chromosome and many wrote about the location of chromosomes in the cell rather than their structure. Weaker candidates did not know the difference between prokaryotes and eukaryotes and some think that prokaryotes are plants and eukaryotes are animals. The term ‘naked’ was often used for DNA not enclosed in a nuclear membrane, when in this context it should be reserved for DNA that is not associated with histone proteins.

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