A-LevelBiologyCell structure9700/22 · May/June 2023 · Q411 Marks

Trypanosoma brucei is a unicellular organism that causes the infectious disease known as sleeping sickness. Insects known as tsetse flies pass on the organism from infected people to uninfected people when male and female tsetse flies feed on human blood.

(a)(i)Draw an arrow on Fig. 4.1 to indicate the location in the cell where ribosomal RNA (rRNA) and proteins are assembled to make ribosomal subunits.[1]
(a)(ii)With reference to Fig. 4.1, explain how the structure labelled X provides evidence that T. brucei is motile (able to move).[2]
(a)(iii)With reference to Fig. 4.1, explain whether T. brucei is a eukaryote or prokaryote.[3]
(b)(i)Malaria is an infectious disease caused by organisms belonging to the genus Plasmodium. State the term used to describe an organism that causes disease.[1]
(b)(ii)Name one of the species of Plasmodium that causes malaria. Plasmodium[1]
(c)Outline the similarities and differences between the modes of transmission of malaria and sleeping sickness.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] label line to any part of nucleolus ; must touch an area of nucleolus
[1] (structure X is a) flagellum ;
[1] presence of microtubules / 9 + 2 (microtubule) arrangement / pattern, (in cross section) ;
[1] flagella enable movement / cell motility ;
[1] T. brucei is a eukaryote because of the presence of a (true) nucleus / nuclear envelope / nuclear membranes ;
[1] T. brucei is a eukaryote because of the presence of mitochondria ;
[1] T. brucei is a eukaryote because of the presence of a nucleolus ;
[1] T. brucei is a eukaryote because of the presence of chromatin ;
[1] T. brucei is a eukaryote because structure X (flagellum) has a 9+2 pattern of microtubules / refers to cytoskeleton / microtubules ;
[1] T. brucei is a eukaryote because it has an endoplasmic reticulum / Golgi body ;
[1] T. brucei is a eukaryote because it lacks a cell wall (unlike prokaryotes which have peptidoglycan cell walls) ;
[1] T. brucei is a eukaryote because its size is greater than 5 µm / larger than typical prokaryotic cells ;
[1] pathogen ;
[1] falciparum / malariae / ovale / vivax / knowlesi ;
[1] Similarity: both diseases are vector-borne / carried by a vector (an insect/fly) ;
[1] Similarity: both diseases involve the vector feeding on human blood (for transmission) ;
[1] Difference: the vector for malaria is a mosquito (Anopheles), whereas the vector for sleeping sickness is a tsetse fly ;
[1] Difference: only female mosquitos feed on blood and transmit malaria, whereas both male and female tsetse flies feed on blood and transmit sleeping sickness (as stated in the question context) ;