IB DP Biology Mock Exam SL Paper 1A Set 4- 2025 Syllabus

IB DP Biology Mock Exam SL Paper 1A Set 4

Prepare for the IB DP Biology Exam with our comprehensive IB DP Biology Exam Mock Exam SL Paper 1A Set 4. Test your knowledge and understanding of key concepts with challenging questions covering all essential topics. Identify areas for improvement and boost your confidence for the real exam

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Question

Dry rot fungus (Serpula lacrymans) releases digestive enzymes to break down dead wood externally.

What form of nutrition is employed by dry rot fungus?

(A) Holozoic
(B) Saprotrophic
(C) Mixotrophic
(D) Autotrophic

▶️ Answer/Explanation

Detailed solution

Nutrition types:

Saprotrophic nutrition: Organisms secrete digestive enzymes onto dead organic matter and absorb the digested nutrients (characteristic of fungi).
Holozoic nutrition: Ingestion of food followed by internal digestion (characteristic of animals).
Mixotrophic: Using both autotrophic and heterotrophic nutrition.
Autotrophic: Producing own food via photosynthesis or chemosynthesis.

Dry rot fungus externally digesting dead wood is classic saprotrophic nutrition.

✅ Answer: (B)

Question

The graph shows yearly fluctuations in atmospheric carbon dioxide in the Northern Hemisphere. There is a noticeable rise in carbon dioxide levels during the winter months.

Which explanation could account for this increase during the winter months?

(A) Increase in atmosphere–ocean diffusion
(B) Decrease in photosynthesis of plants
(C) Increase in respiration of all organisms
(D) Decrease in combustion from wildfires

▶️ Answer/Explanation

Detailed solution

The seasonal CO₂ fluctuation is primarily driven by the balance between photosynthesis and respiration in terrestrial ecosystems:

Summer: High photosynthesis rates remove CO₂ from the atmosphere
Winter: Photosynthesis decreases dramatically (especially in deciduous forests), while respiration continues, leading to net CO₂ release

Analysis of options:

(A) Increase in atmosphere–ocean diffusion → Not the primary cause of seasonal fluctuations
(B) Decrease in photosynthesis of plants → Correct. This is the main reason for winter CO₂ increases
(C) Increase in respiration of all organisms → Respiration rates generally decrease in winter due to colder temperatures
(D) Decrease in combustion from wildfires → Wildfires are more common in summer, not winter

✅ Answer: (B)

Question

What results from an increase in global temperatures?

(A) An increase in absorption of solar radiation decreases poleward shift of temperate species.
(B) Release of carbon dioxide from the deep ocean causes decreased rates of decomposition.
(C) Release of methane from melting permafrost causes a decrease in absorption of solar radiation.
(D) Loss of snow and ice causes an increase in absorption of solar radiation.

▶️ Answer/Explanation

Detailed solution

Global warming feedback mechanisms:

(A) Incorrect – poleward shifts increase, not decrease
(B) Incorrect – CO₂ release increases decomposition rates
(C) Incorrect – methane is a greenhouse gas that increases heat absorption
(D) Correct – ice-albedo feedback: loss of reflective snow/ice increases solar radiation absorption, warming Earth further

✅ Answer: (D)

IB DP Biology Mock Exam SL Paper 1A Set 4- 2025 Syllabus