DP Biology (first assessment 2025)

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Question 23M.2.SL.TZ1.d

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Date May 2023 Marks available [Maximum mark: 3] Reference code 23M.2.SL.TZ1.d
Level SL Paper 2 Time zone TZ1
Command term Explain Question number d Adapted from N/A
d.
[Maximum mark: 3]
23M.2.SL.TZ1.d

Explain how the population of fish in a pond could be estimated using the capture-mark-release-recapture method.

[3]

Markscheme
  1. random sample is captured and marked/tagged (in a manner that will not harm fish);
  2. captured sample is released and allowed to mix with general population
    OR
    captured sample is released then wait a few days/weeks;
  3. second sample is captured and both the total number and the number of marked fish counted;
  4. ratio of recaptured marked fish to number in second sample = the ratio of the number in the first sample marked and released to the population size
    OR
    Population Size = n1×n2n2
    n1 = number in first sample marked
    n2 = number in second sample
    n3 = number of recaptured individuals marked

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