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Question 23M.3.HL.TZ2.12

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Date May 2023 Marks available [Maximum mark: 4] Reference code 23M.3.HL.TZ2.12
Level HL Paper 3 Time zone TZ2
Command term Discuss, State Question number 12 Adapted from N/A
12.
[Maximum mark: 4]
23M.3.HL.TZ2.12

A computer model simulation was proposed to assess the removal of extracellular polymeric substances (EPS) from biofilms by using a detachment-promoting agent (DPA).

Simulations on a 60-day-old biofilm after 6 minutes of treatment with DPA and on the same biofilm after 84 minutes of treatment with DPA are shown as a 3D view and a cross section. Dark grey represents bacteria and light grey shows the EPS.

[Source: Used with permission Microbiology Society, from Xavier, J.B., Picioreanu, C., Rani, S.A., van Loosdrecht, M.C.M. and
Stewart, P.S., 2005. Biofilm-control strategies based on enzymic disruption of the extracellular polymeric substance
matrix – a modelling study. Microbiology 151, pp. 3817–3832; permission conveyed through Copyright Clearance
Center, Inc.]

(a)

State one reason, other than the formation of an EPS, for the high resistance to antimicrobial agents in biofilm microorganisms.

[1]

Markscheme
  1. quorum sensing;
  2. high biomass density;
  3. low/no cell division;
  4. limited supply of nutrients;
  5. less penetration/diffusion of substances;
  6. emergent properties;
Examiners report

Answers were mixed about the resistance of biofilms.

(b)

Scientists concluded from this simulation that the detachment of the EPS by DPA will help in the removal of the biofilm. Discuss the support for this conclusion shown by the data.

[2]

Markscheme

Supports

  1. results show that DPA removed outer layers / reduced EPS (of biofilm);
  2. total surface area reduced after 84 min DPA;

Does not support

  1. bacteria still present;
  2. it is only a simulation / needs to be investigate experimentally;
Examiners report

Answers were mixed about the the usage of DPA for biofilm removal.

(c)

State the effect of the DPA on the bacterial concentration of the remaining biofilm.

[1]

Markscheme

no change/slight decrease;

Examiners report

Answers were mixed about its effect on bacterial concentration.