IB Biology HL A3.1 Diversity of organisms 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
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Question 1

Multiple choiceMedium1 mark

The key is used for three local pond species. A field team identifies an observed animal and compares a barcode from pond-water environmental DNA (eDNA) with reference barcodes. The animal has no shell and six legs; the sample barcode is CTAG. Which pair gives the animal’s key identification and the species detected in the water sample, respectively?

Dichotomous key

FeatureIdentification or route
Shell presentPond snail
Shell absentGo to 2
Six legsWater beetle
More than six legsFreshwater shrimp

Reference barcodes

SpeciesBarcode
Pond snailGACT
Water beetleTGCA
Freshwater shrimpCTAG
Show answer and explanation

Answer: A. The key routes an animal with no shell to the next distinction, where six legs identifies a water beetle. The eDNA barcode CTAG matches the freshwater shrimp reference barcode.

B: identifies the observed animal correctly but assigns the sample barcode to the pond snail, whose barcode is GACT.
C: matches the sample barcode correctly but selects the shell-present route for the observed animal.
D: swaps the key identification and the species identified from the eDNA barcode.
Remember: a dichotomous key uses observable features; an eDNA barcode is compared with reference barcodes.

Question 2

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]

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