19.1

Energy flow

Cambridge IGCSE Biology (0610)  · Unit 19: Organisms and their environment  · 10 flashcards

Energy flow is topic 19.1 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 19 — Organisms and their environment , alongside Food chains and food webs, Nutrient cycles and Populations.  In one line: The Sun is the primary source of energy for nearly all biological systems on Earth. Plants capture this light energy and convert it into chemical energy via photosynthesis, which then fuels ecosystems.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across 11 questions worth 144 marks (around 2.1% of all Biology marks in those years).

The deck below contains 10 flashcards — 4 definitions, 2 key concepts and 4 process cards — covering the precise wording mark schemes reward.  Use the 4 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

The principal source of energy input to biological systems

The Sun is the primary source of energy for nearly all biological systems on Earth. Plants capture this light energy and convert it into chemical energy via photosynthesis, which then fuels ecosystems.

What the Cambridge 0610 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. State State that the Sun is the principal source of energy input to biological systems
  2. Describe Describe the flow of energy through living organisms, including light energy from the Sun and chemical energy in organisms, and its eventual transfer to the environment
Definition Flip

What is the principal source of energy input to biological systems?

Answer Flip

The Sun is the primary source of energy for nearly all biological systems on Earth. Plants capture this light energy and convert it into chemical energy via photosynthesis, which then fuels ecosystems.

Definition Flip

What form of energy is captured by plants during photosynthesis?

Answer Flip

Plants capture light energy from the Sun during photosynthesis. This light energy is converted into chemical energy stored in glucose.

Example: a maize plant in a field converts sunlight into glucose, providing energy for its growth and, ultimately, food for humans and animals.
Definition Flip

What type of energy is stored in the glucose produced during photosynthesis?

Answer Flip

Glucose stores chemical energy. This chemical energy is released during respiration to power cellular activities.

Example: glucose is broken down in root cells to provide energy for active transport of mineral ions from the soil.
Key Concept Flip

How does energy flow from plants to other organisms in an ecosystem?

Answer Flip

Energy flows from plants to other organisms when herbivores consume plants. For instance, a caterpillar eats a leaf, obtaining the chemical energy stored in the plant's tissues. This energy is then used by the caterpillar for growth and movement.

Key Concept Flip

What process releases the chemical energy stored in glucose within organisms?

Answer Flip

Cellular respiration releases the chemical energy stored in glucose. This process occurs in both plants and animals.

Example: muscle cells use respiration to convert glucose into energy for muscle contraction.
Key Concept Flip

In what form is energy eventually transferred to the environment?

Answer Flip

Energy is eventually transferred to the environment as heat.

Example: when animals respire, some energy is lost as heat due to the inefficiency of metabolic processes, warming the surrounding environment.
Key Concept Flip

Explain how energy is transferred from the sun to a lion.

Answer Flip

Energy from the sun is captured by plants during photosynthesis and stored as chemical energy. A zebra eats the plant, transferring the chemical energy to the zebra. A lion then eats the zebra, transferring the chemical energy up the food chain to the lion.

Key Concept Flip

Describe the role of decomposers in energy transfer.

Answer Flip

Decomposers like fungi and bacteria break down dead organisms and waste products, releasing nutrients back into the environment. While they gain energy from this process, a significant portion is lost as heat during decomposition.

Key Concept Flip

Why is energy transfer between trophic levels inefficient?

Answer Flip

Energy transfer is inefficient because organisms use energy for their own metabolic processes (respiration, movement), and some energy is lost as heat to the environment at each trophic level. Only a small portion of energy consumed is converted into new biomass.

Definition Flip

What is a food web?

Answer Flip

A food web is a complex network of interconnected food chains within an ecosystem. It represents the flow of energy and nutrients between different organisms. An example is how grass is eaten by rabbits, and rabbits are eaten by foxes.

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18.3 Selection 19.2 Food chains and food webs

Key Questions: Energy flow

What is the principal source of energy input to biological systems?

The Sun is the primary source of energy for nearly all biological systems on Earth. Plants capture this light energy and convert it into chemical energy via photosynthesis, which then fuels ecosystems.

What form of energy is captured by plants during photosynthesis?

Plants capture light energy from the Sun during photosynthesis. This light energy is converted into chemical energy stored in glucose.

Example: a maize plant in a field converts sunlight into glucose, providing energy for its growth and, ultimately, food for humans and animals.
What type of energy is stored in the glucose produced during photosynthesis?

Glucose stores chemical energy. This chemical energy is released during respiration to power cellular activities.

Example: glucose is broken down in root cells to provide energy for active transport of mineral ions from the soil.
What is a food web?

A food web is a complex network of interconnected food chains within an ecosystem. It represents the flow of energy and nutrients between different organisms. An example is how grass is eaten by rabbits, and rabbits are eaten by foxes.

Tips to avoid common mistakes in Energy flow

More topics in Unit 19 — Organisms and their environment

Energy flow sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

19.2 Food chains and food webs

10 flashcards
19.3 Nutrient cycles

12 flashcards
19.4 Populations

12 flashcards

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

food chain food web producer consumer primary consumer secondary consumer tertiary consumer herbivore carnivore omnivore decomposer trophic level pyramid of numbers pyramid of biomass pyramid of energy energy transfer energy loss

Key terms covered in this Energy flow deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

The principal source of energy input to biological systems
What form of energy is captured by plants during photosynthesis
What type of energy is stored in the glucose produced during photosynthesis
Food web

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How to study this Energy flow deck

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