DP Biology (last assessment 2024)

Test builder »

Question 18M.2.SL.TZ2.2

Select a Test
Date May 2018 Marks available [Maximum mark: 8] Reference code 18M.2.SL.TZ2.2
Level SL Paper 2 Time zone TZ2
Command term Distinguish, Explain, Label, Outline Question number 2 Adapted from N/A
2.
[Maximum mark: 8]
18M.2.SL.TZ2.2
(a)

Label the parts of the DNA diagram indicated by I, II, III and IV.

[2]

Markscheme

a. I. cytosine 

b. II. sugar-phosphate/covalent/phosphodiester bond 

c. III. phosphate 

d. IV. deoxyribose

Award [1] for any two correct responses.

(b.i)

Explain how model making helped Watson and Crick to establish the structure of DNA.

[2]

Markscheme

a. decided to combine what was known about chemical content of DNA with information from X-ray diffraction studies OWTTE.

b. built scale models of components of DNA 

c. then attempted to fit them together in a way that agreed with the data «from separate sources» 

d. made several arrangements of scale model until found best one that fitted all the data

(b.ii)

Distinguish between the chromosomes of eukaryotic cells and prokaryotic cells.

[1]

Markscheme

a. associated with «histone» proteins in eukaryotes but not prokaryotes

b. is linear in eukaryotes but circular in prokaryotes 

c. in cytoplasm in prokaryotes, but within nucleus in eukaryotes.

(c.i)

Outline the role of the enzyme helicase in replication.

[1]

Markscheme

unwinds/separates strands/double helix (by breaking hydrogen bonds) 

(c.ii)

Outline the role of the enzyme DNA polymerase in replication.

 

[2]

Markscheme

a. links nucleotides together to form a new strand of DNA 

b. uses pre-existing strand of DNA as template 

c. makes covalent bonds between nucleotides

Syllabus sections