Home / IB DP Biology- D4.2 Stability and change- IB Style Questions For HL Paper 1A

IB DP Biology- D4.2 Stability and change- IB Style Questions For HL Paper 1A -New Syllabus

IBDP Biology HL Paper 1 -All Chapters

Question

Surtsey, a volcanic island approximately 32 km from the south coast of Iceland, was formed by volcanic eruptions between 1963 and 1967. It has been legally protected since its formation and is free from human interference.

What changes are likely to have been observed since the formation of Surtsey?

(A) Cyclical succession as the climax community changes
(B) Secondary succession when animal species arrived
(C) Arrested succession due to the drainage of wetlands
(D) Primary succession including an increase in size of plants
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{D}} \)

Surtsey began as bare volcanic rock with no soil or living organisms, so it undergoes primary succession. Over time, soil develops and larger plant species gradually replace pioneer species as the ecosystem becomes more established.

Question

During the process of primary succession, how does the structure of an ecosystem typically change over time?

A. Saprotrophs are the first organisms to inhabit bare rock.
B. The level of primary productivity remains constant.
C. Species diversity tends to decrease as succession progresses.
D. The complexity and interconnections of food webs increase over time.

▶️ Answer/Explanation
In primary succession, pioneer species such as lichens and mosses first colonize bare rock and gradually create soil, allowing more complex plant and animal species to establish. As succession continues, both species diversity and the complexity of food webs increase, forming a stable climax community over time.
✅ Answer: (D) There is an increase in the complexity of food webs.

Question

Increased leaching of nitrogen fertilizers disrupts the stability of aquatic ecosystems. What change is expected if nitrogen leaches into a lake over time?

(A) Wilting of surface plants
(B) Increased biochemical oxygen demand (BOD)
(C) Weakened mollusc shells
(D) Bioaccumulation of pollutants at higher trophic levels
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{B}} \)

Nitrogen fertilizer runoff causes eutrophication, leading to excessive growth of algae. When the algae die, decomposers break them down, consuming large amounts of dissolved oxygen. This results in an increase in biochemical oxygen demand (BOD) and can lead to oxygen depletion, harming aquatic organisms.

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