Home / IB DP Biology- C4.2 Transfers of energy and matter – IB Style Questions For SL Paper 1A

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

IBDP Biology Paper 1 - 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

In a stable natural ecosystem, how is the supply of nutrients and energy maintained?

A. Nutrients and energy are efficiently cycled within the ecosystem.
B. Energy from the Sun is cycled through the food chains, while nutrients are constantly lost.
C. Nutrients are efficiently cycled within the ecosystem, while there is a constant flow of energy.
D. Energy is cycled through photosynthesis and respiration, while food chains ensure that nutrients flow through the ecosystem.

▶️ Answer/Explanation

Answer: C. Nutrients are efficiently cycled within the ecosystem, while there is a constant flow of energy.

Explanation: Ecosystem energy and nutrient flow

In a stable natural ecosystem:

  • Nutrients (like carbon, nitrogen, and phosphorus) are recycled through processes such as decomposition, excretion, and uptake by plants. These elements are reused within the ecosystem.
  • Energy, however, does not cycle. It flows in one direction — from the Sun, through producers (via photosynthesis), to consumers, and finally to decomposers. At each step, energy is lost as heat, mainly through metabolism. Therefore, new energy must continuously enter the system from sunlight.

Answer Evaluation:

A. Incorrect – While nutrients are cycled, energy is not. It flows through the system and cannot be reused once lost as heat.

B. Incorrect – This reverses the truth. Nutrients are recycled, not constantly lost, while energy flows and is not recycled.

C. Correct – This accurately describes that nutrients are recycled within the ecosystem, and energy flows in from the Sun and is lost, requiring constant input.

D. Incorrect – Energy is not cycled through photosynthesis and respiration; it is transformed and eventually lost as heat.

Question

The diagram shows part of a food chain. The left box represents producers and the right box primary consumers. Arrows show energy flows.

Which forms of energy are represented by \( X \) and \( Y \)?

▶️ Answer/Explanation

Answer: D. light \((X)\), chemical \((Y)\)

Explanation:

  • \(X\) (into producers): Producers (e.g., green plants) capture light energy from the Sun via photosynthesis. Hence, \(X = \text{light}\).
  • \(Y\) (from producers to primary consumers): Energy passed along the food chain is stored as chemical energy in producer biomass (e.g., glucose) and transferred to consumers when they feed. Hence, \(Y = \text{chemical}\).

Evaluation of other options:

Option\(X\)\(Y\)Reason
AheatkineticHeat is generally lost from systems and is not the input to producers; kinetic energy is not the primary form transferred in food chains.
BheatchemicalProducers are powered by light, not heat.
ClightheatWhile \(X\) is correct, \(Y\) should be chemical energy transferred in biomass, not heat.
DlightchemicalMatches standard energy transformations in food chains.
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