DP Biology (first assessment 2025)

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Question 23M.2.SL.TZ1.1g

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Date May 2023 Marks available [Maximum mark: 3] Reference code 23M.2.SL.TZ1.1g
Level SL Paper 2 Time zone TZ1
Command term Evaluate Question number g Adapted from N/A
g.
[Maximum mark: 3]
23M.2.SL.TZ1.1g

In each forest, there are two or three trial plots per CO2 treatment. The bar chart shows the allocation of carbon from net primary production to different parts of the trees in these trial plots.

[Source: Walker, A.P., De Kauwe, M.G., Medlyn, B.E., et al., 2019. Decadal biomass increment
in early secondary succession woody ecosystems is increased by CO2 enrichment.
Nature Communications, [e-journal] 10, 454. https://doi.org/10.1038/s41467-019-08348-1.
Open access.]

(g)

Evaluate the evidence from the bar chart that increases in carbon dioxide cause increases in carbon storage in young, developing forests.

[3]

Markscheme
  1. more carbon stored/allocated (by the tree as a whole) with elevated carbon dioxide;
  2. evidence (from the bar chart) is strong (for the trend/hypothesis);
  3. all elevated plots have more carbon stored than all ambient plots in all sites/no overlap;
  4. more/most carbon allocated to wood (in stems and roots) with elevated carbon dioxide;
  5. more carbon allocated to narrow roots/leaves with elevated carbon dioxide;
  6. narrow roots increase most in Oak Ridge;
  7. most increase in wood (in stems and roots) in Rhinelander and Duke;
  8. much/more variation between plots at Oak Ridge (than at Rhinelander and Duke);
  9. no error bars so significance of differences is uncertain;

Accept mpd and mpe if the answer refers only to Rhinelander and Duke.

Allow mph if the answer describes an anomaly at Oak Ridge that does not follow the trend seen in Rhinelander and Duke.

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