Question
The effectiveness of three different treatments for killing the pathogenic bacterium Staphylococcus aureus found on solid surfaces was assessed. Each treatment contained a probiotic cleaning hygiene system (PCHS), specific bacteriophages alone (SBP), or a combination of both (SBP+PCHS). A control was set up using water. The bar chart shows the percentage of S. aureus remaining on solid surfaces at two different times after applying the treatments and the control.
(a) Deduce with a reason the most efficient treatment to eliminate S. aureus from solid surfaces.
(b) S. aureus often forms biofilms in water systems together with Pseudomonas aeruginosa. Outline the benefits of using bacteriophages rather than chemicals to eliminate biofilms from water systems.
(c) Describe how Pseudomonas can be used to reduce pollution caused by methyl mercury.
Answer/Explanation
Answer:
(a)
SBP+PCHS as more bacteria removed/killed
OR
SBP+PCHS as the effect lasts longer/more than 3 days;
(b)
a. bacteriophages (are viruses that) infect bacteria;
b. they can spread through entire biofilm to kill bacteria;
OR
chemicals only kill bacteria near the surface of biofilm
c. polysaccharide matrix/EPS/biopolymers act as a (physical) barrier to
chemicals;
d. bacteriophages are specific/can be added to destroy a specific pathogen;
e. chemicals can contaminate water
OR
can lead to bacteria resistant to the chemical;
(c)
a. bioremediation;
b. Pseudomonas putida used;
c. methyl mercury converted/decomposed to (methane and) mercury ions;
d. mercury ions turned into mercury (by other bacteria);
e. insoluble mercury can be separated from waste water;
Question
b. Define indicator species. [1]
c. Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant. [3]
e. Determine whether islands are open or closed ecosystems. [1]
▶️Answer/Explanation
Markscheme
organism that is present/absent when specific environmental conditions exist
OR
organism used to assess a specific environmental condition
a. example eg: DDT / mercury / cadmium
b. substance accumulates in «fat» tissue/not excreted «when consumed»
c. contaminated organisms consumed «in large quantities» by higher level consumers
d. pollutant becomes more concentrated at each higher trophic level / through the food chain
e. some pollutants are more likely to be biomagnified «accumulate in fat tissue»
OR
some organisms are more likely to be affected by biomagnification than others
OR
biomagnification not the same at each trophic level
Only [2] if verified example not given.
closed because islands do not exchange matter/nutrients with surroundings
OR
open because islands do exchange matter/nutrients with surroundings
Question
a. Distinguish between fundamental niche and realized niche.[1]
b. Outline the impact of competition on the niche of an organism.[2]
c. Outline the characteristics of keystone species in an ecosystem.[1]
▶️Answer/Explanation
Ans:
a. fundamental is the potential (niche) and realized is the actual (niche)
OWTTE.
b. a. competition can limit the niche
b. competition can limit resources
c. when competition is removed the niche can expand
d. can result in exclusion or removal of a species from a niche / only one species can occupy a niche
c. a. keystone species has a strong/disproportionate effect on a community/food web/ecosystem
b. absence of keystone species would completely alter the ecosystem
Question
Gersmehl diagrams for two ecosystems are shown.
a. Identify the processes represented by the arrows labelled A and B in both diagrams.[2]
b. Deduce, with a reason, which ecosystem is representative of a tropical rainforest.[2]
▶️Answer/Explanation
Ans:
a. a. Process A: decomposition/decay
b. Process B: leaching/erosion/run-off/weathering
b. a. ecosystem I
b. low levels of litter due to high rates of decomposition OR high amounts of biomass related to high rates of productivity OR weathering/leaching due to high rates of precipitation