IB Biology HL Theme A: Unity and diversity questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type
Multiple choiceWritten
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Question 1

Paper 2Hard16 marks

Two bacterial lineages, A and B, reproduce by binary fission. They can be distinguished by an inherited feature unrelated to gene marker M. At the start of an investigation, M was detected in all sampled A colonies and none of the B colonies. A mixed culture contained both lineages; a control culture contained B only. At each time point, 100 colonies of each lineage were sampled and tested for M.

01020300102030405060708090100Generations after start of cultureColonies carrying M (%)Percentage of sampled colonies carrying gene marker M○ Lineage A, mixed culture△ Lineage B, mixed culture□ Lineage B, B-only control
(a)

State two features of the biological species concept used to decide whether populations belong to the same species.

[2]
(b)

Describe the change in the percentage of lineage B colonies carrying M in the mixed culture over the 30 generations.

[2]
(c)

Suggest the most likely explanation for the appearance of M in lineage B, using all three series in Figure 1.

[3]
(d)

Two populations, P and Q, of another organism reproduce only asexually. Explain why the biological species concept cannot establish whether P and Q are the same or different species.

[3]
(e)

A student concludes that A and B must be one biological species because they share M after mixing, and that P and Q must be different species because they cannot interbreed. Assess these two conclusions, using Figure 1 and the biological species concept.

[6]

Question 2

Paper 2Hard16 marks

Ecologists surveyed the same twelve 1 ha woodland plots in 2012, 2018 and 2024. Expert teams used the same method, visited at the same time of year and spent the same amount of time surveying each plot. The table shows the numbers of individuals recorded for six native bird species. A zero indicates that no individuals of that species were recorded.

Species201220182024
A405070
B302412
C20144
D1072
E850
F200

A citizen-science portal also collected observations in the surrounding landscape. A record is one submitted sighting, not a count of unique species. The portal did not use fixed observer-hours or fixed locations, and sightings were not independently checked.

YearRecords submittedContributorsHabitat types sampled
20121 200803
20245 1006009

Other estimates for the same landscape were:

Measure20122024
Human population42 00059 000
Native woodland remaining / ha1 200780
Woodland converted to agriculture or settlement since 2012 / ha0420
Plots occupied by an invasive alien plant / 1217
(a)

Calculate the percentage change in recorded bird species richness between 2012 and 2024.

[2]
(b)

Describe how species richness and evenness changed in the bird survey between 2012 and 2024.

[3]
(c)

State one benefit of citizen-science observations and explain why the increase in portal records alone does not establish an increase in biodiversity.

[4]
(d)

A conservation group concludes that biodiversity in this landscape is recovering and that any decline in the bird survey was caused solely by human population growth. Evaluate whether the data support these conclusions.

[7]

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