IB DP Biology Mock Exam HL Paper 1B Set 1 - 2025 Syllabus
IB DP Biology Mock Exam HL Paper 1B Set 1
Prepare for the IB DP Biology Exam with our comprehensive IB DP Biology Exam Mock Exam HL Paper 1B Set 1. Test your knowledge and understanding of key concepts with challenging questions covering all essential topics. Identify areas for improvement and boost your confidence for the real exam
Question
Organisms often release chemicals when attacked as part of their defence system. Scientists studied lima bean plants (Phaseolus lunatus) infested with either an armyworm, Spodoptera exigua, or a herbivorous mite, Tetranychus urticae. Both organisms feed on lima bean leaves, causing the leaves to release chemicals.
The study was conducted to see which defence chemicals were produced by lima bean leaves when infested by armyworms or herbivorous mites. The scientists identified a mixture
of compounds (C) released by the plant when attacked. Two of the chemicals in this mixture were identified (C1 and C2). The scientists hypothesized that the defence chemicals in C act as signals to produce other chemicals (X, Y and Z) that are also involved in the defence of the plant.
The graphs show the amounts of chemicals X, Y and Z produced when the plants were infested by either one of the two herbivores or treated with the different chemicals C1 or C2.
(a) Distinguish between the data for the leaves infested with the armyworm and the leaves infested with the herbivorous mite.
(b) Compare and contrast the effects of treatment of the leaves using C1 and C2 with the effects of infestation.
RNA was collected from leaves of the plants after each treatment (armyworm, herbivorous mite and the chemicals C1 and C2). DNA copies of the extracted RNA were made by a process called reverse transcription. Targeted genes in the DNA were then amplified.
(c) Identify the process that was used to amplify the targeted genes.
The scientists then used the transcribed DNA of each treatment to study the activation of three genes of the plants’ defence system. The DNA was separated by gel electrophoresis. The activation was tested one hour after treatment and again after 24 hours.
(d) Deduce, with a reason, which gene is first transcribed when exposed to C2.
(e) Each gene is activated by one or more of the treatments. From the gel electrophoresis data, discuss the impact of the herbivorous mite infestation on gene activation compared to treatment with C1 and C2.
(f) Using the gene activation data, deduce, giving two reasons, whether the armyworm or the herbivorous mite has infested lima bean plants over a longer period of time.
Answer/Explanation
Ans:
a)
a. armyworm «infestation» produced more X than Y than Z/decreasing amounts AND herbivorous mite showed the opposite pattern/more Z than Y than X
b. armyworm «infestation» produced more X than herbivorous mite
c. armyworm «infestation» produced more Y than herbivorous mite / Y is the middle value for both
d. armyworm «infestation» produced less Z than the herbivorous mite
e. other valid distinction
b)
a. C1 caused the leaf to produce two of the same chemicals/Y and Z as the attack of herbivorous mites in a similar pattern «but in lower quantities»
b. C1 produces the least «total» amount of chemicals of all the treatments
c. C2 has very similar pattern to those caused by the armyworms «but in lower quantities»
d. both herbivores caused a greater production of chemicals/all three chemicals compared to either C1 or C2
e. armyworms cause the greatest total amount of chemical production of any of the other treatments
f. other valid comparison of chemical effect versus herbivore effect
c) PCR Accept RT PCR.
d) gene 1 is first transcribed «after C2 treatment» as it shows activation after one hour
e )
a. herbivorous mites induce activation of gene 2 first «at 1 hour» and then also gene 1 and gene 3 «at 24 hours»
OR
herbivorous mite «infestation» is the only treatment to affect all three genes/leads to greater gene expression overall
b. gene 2 activation similar for mite and C1 «at both 1 and 24 hours»
c. gene 3 activation similar for mite and C2 «both at 24 hours»
d. gene 1 activation slower for mite compared to C2 but more intense (than C2 at 24 hours)
e. gene 1 and gene 3 expressed in higher amounts «after 24 hours» in mite infestation compared to C2 Both parts OWTTE required for mpd.
f)
a. the greater «gene expression» response of the lima bean plant to the mite infestation indicates longer evolutionary relationship
b. herbivorous mites cause more genes to be expressed/higher intensity of gene activation