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Date May 2018 Marks available 1 Reference code 18M.3.SL.TZ2.9
Level Standard level Paper Paper 3 Time zone Time zone 2
Command term State Question number 9 Adapted from N/A

Question

A build-up of salt (NaCl) in soil is known as salinization. This can make the soil unsuitable for agriculture. One strategy that has been used to address this problem is to add compost mixed with salt-metabolizing bacteria to this soil. The bacteria loosen the association of the Na+ with the soil and allow it to be washed out by rain more effectively. The graph shows the effect of bacteria over time on the amount of salt in the soil.

Another strategy for addressing soil salinization is to use genetically modified plants. A gene from Arabidopsis thaliana that codes for a vacuole membrane protein (AtNHX1) known as the Na+/H+ antiport was inserted into tomato plants. The transgenic plants increased storage of salt in their leaves yet the tomato fruit grew normally compared to unmodified plants.

Outline the trend in amount of salt in the soil over the study period.

[1]
a.

State the name of the strategy that involves the use of organisms to remove toxic substances from a contaminated site.

[1]
b.

Suggest how these genetically modified tomato plants could be useful to farmers.

[1]
c.i.

Explain how a researcher could determine whether other species contained similar sequences to the AtNHX1 gene.

[3]
c.ii.

Markscheme

decrease with time «exponential»
OR
negative correlation

a.

bioremediation

b.

a.GM tomatoes could be used to grow a crop on salinized soil «that otherwise would kill the plants» 

b.tomato crop could be used to remove salt from the soil «if the harvested crop was removed»
OR
phytoremediation

c.i.

a. use bioinformatics tools «to search for similar sequences» 

b. conduct database/Blast search 

c. evaluate sequence alignment

c.ii.

Examiners report

 

a.

 

b.

 

c.i.

 

c.ii.

Syllabus sections

Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics) » B.3 Environmental protection
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