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IB DP Biology- C4.2 Transfers of energy and matter- IB Style Questions For HL Paper 1A -FA 2025

IBDP Biology HL Paper 1 -FA 2025- All Chapters

Question

Which group of organisms derives energy by oxidizing simple inorganic compounds rather than using sunlight or organic molecules?

A. Photoautotrophs
B. Heterotrophs
C. Chemoautotrophs
D. Saprotrophs

▶️ Answer/Explanation
Chemoautotrophs are organisms that obtain energy through the oxidation of inorganic substances such as hydrogen sulfide, ammonia, or iron ions. They use this chemical energy to fix carbon dioxide and synthesize organic molecules — a process known as chemosynthesis.
✅ Answer: (C) Chemoautotrophs

Question

The three-toed sloth, Bradypus variegatus, lives in tree tops where it feeds on leaves. It also feeds on algae and fungi which live in its fur.

In which trophic group should the three-toed sloth be classified?

A. Autotroph

B. Consumer

C. Detritivore

D. Saprotroph

▶️Answer/Explanation

Answer: B. Consumer

Explanation:

The three-toed sloth (Bradypus variegatus):

  • Feeds on leaves → These are living plant materials.
  • Feeds on algae and fungi in its fur → These are also living organisms (or recently alive).

Trophic Group Analysis:

A. Autotroph
Incorrect: Autotrophs make their own food through photosynthesis or chemosynthesis (e.g., plants, algae). The sloth does not produce its own food.

B. Consumer
Correct: Consumers eat other living organisms. Since the sloth eats leaves, algae, and fungi, it fits into this group.

C. Detritivore
Incorrect: Detritivores eat non-living organic matter (dead material). The sloth feeds on living organisms, not detritus.

D. Saprotroph
Incorrect: Saprotrophs (like fungi and bacteria) externally digest dead organic matter and absorb nutrients. The sloth does not externally digest anything.

 Question

The diagram shows the food web for an aquatic ecosystem in which letters R–Z represent individual species.

Which organism is a tertiary consumer?

A. Organism T

B. Organism U

C. Organism W

D. Organism Y

▶️Answer/Explanation

Answer: B. Organism U

Explanation:

A tertiary consumer eats a secondary consumer, which eats a primary consumer, which eats a producer.

Step-by-step breakdown:

  1. Producers (e.g., R, S, T): No incoming arrows → they produce energy, not consume others.

  2. Primary Consumer (e.g., W): Eats producers (R, S, T) → gets energy directly from plants/algae.

  3. Secondary Consumers (e.g., V, X, Y): Eat primary consumer (W).

  4. Tertiary Consumers: Eat secondary consumers: U eats V, Z eats X and Y

    •  

Option Analysis:

A. T → A producer.

B. U → Eats V, a secondary consumer → tertiary consumer 

C. W → Eats producers → primary consumer 

D. Y → Eats W → secondary consumer 

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