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IB ESS 2.5 Zonation, Succession and Change

Practise distinguishing spatial zonation from temporal succession, using transect and case-study evidence to explain soil development, diversity and resilience after disturbance.

Syllabus
First assessment 2026
Course
ESS SL
Level
SL

Exam points

  • distinguish spatial zonation from temporal succession using gradients, transects and primary or secondary examples
  • explain how colonisation, humus, nutrient cycling and roots increase soil fertility, diversity and resilience

2.5 Zonation, succession and change question 1

[Maximum number: 1]
Salinity variation in the Large Ocean Management Area

Figure:Salinity variation in the Large Ocean Management Area

Water-surface temperature variation across the LOMA

Figure:Water-surface temperature variation across the LOMA

temperature scale

Figure:temperature scale

Suggest one reason for the zonation seen in Figure: Water-surface temperature variation across the LOMA.

2.5 Zonation, succession and change question 2

[Maximum number: 3]
Beaver-dam succession sequence — panel A

Figure:Beaver-dam succession sequence — panel A

Beaver-dam succession sequence — panel B

Figure:Beaver-dam succession sequence — panel B

Beaver-dam succession sequence — panel C

Figure:Beaver-dam succession sequence — panel C

Beaver-dam succession sequence — panel D

Figure:Beaver-dam succession sequence — panel D

Suggest how an ecologist might measure the changes in one abiotic factor along a transect from a beaver marsh, through beaver meadow to the adjoining forest.

2.5 Zonation, succession and change question 3

[Maximum number: 7]
Stages of ecological succession after fire

Figure:Stages of ecological succession after fire

Question (a)

(a)

Outline two reasons why the climax community in the succession model shown above is more stable than the intermediate community.

[ 2 ]

Question (b)

(b)

Distinguish between zonation and succession.

[ 1 ]

Question (c)

(c)

Outline two ways in which the food web is likely to change as a result of succession.

[ 2 ]

Question (d)

(d)

Outline two ways in which the soil quality in the pioneer stages of the succession model shown above will differ from that in the climax ecosystem.

[ 2 ]
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