Home / IB DP Biology- B4.2 Ecological niches- IB Style Questions For HL Paper 1A

IB DP Biology- B4.2 Ecological niches- IB Style Questions For HL Paper 1A -FA 2025

IBDP Biology HL Paper 1 -FA 2025- All Chapters

Question

What happens during competitive exclusion when two species share overlapping ecological niches?

I. They compete for identical resources and cannot coexist in the same niche.
II. Competing species are regulated by predators within the ecosystem.
III. Both species become confined to a smaller portion of their fundamental niche.

A. I and II only
B. I and III only
C. III only
D. I, II and III

▶️ Answer/Explanation
The competitive exclusion principle states that two species competing for the same resources cannot coexist indefinitely in the same ecological niche. One species typically outcompetes the other, forcing it to occupy a different or smaller part of its fundamental niche. This makes statements I and III correct.
✅ Answer: (B) I and III only

Question

The diagram shows flows of energy and matter in an ecosystem. What do the letters P, Q and R represent?

▶️ Answer/Explanation

Ans. C

Diagram breakdown:

  • P → Producers (energy): P is the energy input to producers.
  • Producers → Consumers: Energy and matter flow from producers to consumers.
  • Consumers → Decomposers: Energy and matter pass from consumers to decomposers.
  • Decomposers → Producers (matter): This shows recycling of nutrients.

Q is connected back to producers and consumers with energy arrows.
R is connected to producers with matter arrows.

What do these flows represent?

P: Energy input to producers → light

Q: Energy lost from system → heat

R: Matter recycled to producers from decomposers → inorganic nutrients

Why others are incorrect:

  • A: Water vapour and nitrates don’t match the energy flow.
  • B: Chemical energy is stored in producers, but the initial energy source is light.
  • D: Chemical energy → carbon dioxide → glucose mixes up matter and energy flows.

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:

Trophic groups classify organisms by how they obtain energy:

  • Autotrophs make their own food (e.g., plants).
  • Consumers eat other organisms.
  • Detritivores feed on dead material but ingest it (e.g., earthworms).
  • Saprotrophs secrete enzymes on dead matter and absorb nutrients (e.g., fungi).

Option Evaluation:

A. Incorrect – Sloths are not autotrophs; they don’t photosynthesize.

B. Correct – Sloths consume leaves and small organisms like algae and fungi. That makes them primary or secondary consumers depending on what they eat.

C. Incorrect – Detritivores eat dead material, which is not the sloth’s main diet.

D. Incorrect – Saprotrophs break down dead organic matter externally. Sloths don’t do this.

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