IB ESS HL 1.2 Systems Question Bank

Valid factors: greater diversity of components/species increases resilience;
complexity of interactions/developed food webs increase resilience; establishment of keystone species increases resilience;
larger storages/stores / more abundant/productive resources (nutrients, water, sunlight, reproductive rates, biomass etc) increase resilience (NB for credit, there must be indication of abundance in these resources, and if multiple examples are given like those in brackets, there is still only [1 max] allowed for this MP);
larger size of the system increases resilience; strong negative feedback systems increase resilience; strong positive feedback mechanisms may decrease resilience; human impact degrading structure/diversity/abundance will decrease resilience;
a steady state equilibrium/balanced inputs and outputs (as in climax communities)
increases resilience; systems being close to a tipping point decrease resilience;

Marking guidance:

Accept converse statements.
Award [1] for each correct factor identified, up to [4 max].
If valid factors are identified, but their effect on resilience is not, award [1] for each TWO factors up to [2 max] (ie FOUR factors). Eg identifying TWO factors and their effect on resilience, along with TWO factors but no specified effect would score [2+1=3] total OR eg TWO factors and their effect, along with ONE with no effect would score $[\mathbf{2} \boldsymbol{+} \mathbf{0} \boldsymbol{=} \mathbf{2}]$ total OR eg FOUR factors with no effect ([1+1=2] total).

A community of trees in a woodland has the following features of a system: individuals/species of trees are the components of the system; these components are interrelated/interdependent/form an integrated whole; eg may regulate populations through competition / contribute to succession of community;
it has flows/transfers of matter/energy between components/storages; eg leaf fall may provide nutrients through decomposition to other trees / pollination/genes/food storage in seeds / glucose is transported from leaves around tree;
components carry out processes/transformations; eg photosynthesis/respiration/growth;
it is an open system exchanging matter and energy with surroundings;
eg absorption of solar energy / provision of nutrients for non-tree species (NB mark for either example of matter or energy, not both);
it has feedback mechanisms to maintain equilibrium/balanced inputs and outputs; eg more seed production → more competition between seedlings → fewer viable offspring / death of trees → more light entering canopy → more tree growth;

Marking guidance:

Award [1] for each correct suggestion, up to [7 max].
Award [4 max] for identifying relevant generic features of system (given above) and [4 max] for examples of these within a tree community (beware of responses that are looking at entire woodland ecosystem as a system rather than the tree community alone). Credit alternative examples of equivalent validity/relevance and detail.

The following guide for using the markbands suggests certain features that may be offered in responses. The five headings coincide with the criteria given in each of the markbands (although "ESS terminology" has been conflated with "Understanding concepts"). This guide simply provides some possible inclusions and should not be seen as requisite or comprehensive. It outlines the kind of elements to look for when deciding on the appropriate markband and the specific mark within that band.

Answers may include:
- understanding concepts \& terminology of greenhouse gases; global warming; thermal expansion; rising sea-level; melting ice caps; salinity; ocean acidification; ozone depletion; UV radiation; global productivity; tropospheric ozone; acid rain (worth noting here that acid rain is NOT a significant cause/contributor to ocean acidification); etc
- breadth in addressing and linking impacts on atmospheric systems (increased $\mathrm{CO}_{2}$; global warming; ozone depletion; tropospheric ozone; acid rain; etc) with disturbances in marine systems (rising sea level; ocean currents; fish migration; acidification; destruction of coral reefs; phytoplankton / marine food chains; etc)
- examples of relevant atmospheric pollutants/disturbances; ocean currents; coral communities; migratory fish; marine food chains; etc
- balanced analysis of the extent to which each atmospheric disturbance causes disturbance in marine systems whether significant, minimal or none at all, acknowledging relevant counter-arguments/alternative viewpoints;
- a conclusion that is consistent with, and supported by analysis and examples given e.g. generally, the statement is valid regarding large scale disturbances to the atmosphere such as global warming and ozone depletion but more localized disturbances like tropospheric ozone and acid rain have fairly minimal impact; NB This is only an example of a possible conclusion. Candidates' conclusions do not have to agree.

Please see markbands on page 21.