IB Biology HL D4.2 Stability and change 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
Multiple choiceWritten
Difficulty
EasyMediumHard

Question 1

Paper 2Medium16 marks

A kelp-forest survey recorded the following data. Sea otters feed on sea urchins, which graze on kelp. Kelp forests provide food and habitat for many species.

YearSea otters counted along a 10 km coastlineSea urchins (individuals m⁻²)Kelp cover (%)
201840882
2021291563
2024162443

Managers also estimated annual replacement and harvest for two renewable resources. Annual replacement is the number of individuals entering the harvestable stock during the year through growth or recruitment.

ResourceAnnual replacementAnnual harvest
Scots pine, a terrestrial plant150 trees year⁻¹180 trees year⁻¹
Atlantic cod, a marine fish30 000 fish year⁻¹24 000 fish year⁻¹
(a)

Describe the patterns in the sea otter, sea urchin and kelp data between 2018 and 2024.

[3]
(b)

Using the data and feeding relationships, explain how a decline in sea otters could affect ecosystem stability and support identifying sea otters as a keystone species.

[4]
(c)

Calculate the percentage of annual replacement harvested for each resource. Show your working.

[4]
(d)

Using your results from (c), assess whether harvesting meets the sustainability criterion for each resource in the year shown.

[3]
(e)

Explain why the results for one year cannot by themselves establish whether each harvest is sustainable over the long term.

[2]

Question 2

Multiple choiceHard1 mark

A record for one region covers four consecutive intervals, each 1 million years long. In each interval, the record identifies the ecosystem type and 10 species groups. The final column shows how many groups are also recorded in the immediately preceding interval. Which conclusion is supported by the complete record?

Time interval (million years ago)Ecosystem typeSpecies groups shared with preceding interval
4–3Forest—
3–2Forest8
2–1Forest3
1–0Forest6
Show answer and explanation

Answer: A. All four consecutive intervals are identified as forest, spanning four million years. Fewer than 10 groups are shared at each transition, so species-group composition changed while the ecosystem type remained forest.
B: Confuses the same number of groups in each interval with the same groups; the overlap values are below 10.
C: Uses species-group turnover to infer ecosystem-type change, although every interval is identified as forest.
D: Stops at the most recent two intervals and overlooks the forest classifications in the earlier intervals.
Remember: continuity of ecosystem type does not require identical species composition.

The best questions are still waiting

Unlock every question in this topic, then type, photograph or draw your answer and have it marked against the markscheme. Find out where you are dropping marks.

Unlock all questionsCompare Student and Student Plus