Hong Kong Primary School Science Curriculum, Grade 4: Where Does My Energy Come From?

Energy in ecosystems does not appear out of nowhere—it flows unidirectionally between organisms through the act of 'feeding'.unidirectional flowA food chain is a scientific model describing this energy transfer pathway. It reveals how organisms capture solar energy through 'producers' and pass it along through 'consumers', ultimately forming a stable structure that sustains life.

Learning Objectives

Describe the roles of different organisms in a simple food chain.
Identify predator-prey relationships.
Understand that organisms compete with each other for limited resources.

Key Vocabulary

Food ChainProducerHerbivoreCarnivorePredatorPreyCompetitionResources

Core Content: Part One – What Is a Food Chain?

A food chain describes the linear relationship of 'who eats whom' among organisms—essentially, the process ofenergy (Energy)transfer within an ecosystem. All organisms need energy to grow and function, and the ultimate source is typically the Sun.

Producer (Producer): Organisms capable of producing their own nutrients (e.g., plants), located at the beginning of the food chain.
Consumer (Consumer): Organisms that obtain energy by consuming other organisms.
Predator and Prey: A predator hunts and consumes its prey.
Competition (Competition): Interaction that occurs when multiple organisms seek the same limited resources.

Ecosystem Roles and Relationships Analysis

Based on what you’ve learned in class, analyze the following interactions among organisms.

In a forest, grass grows abundantly, providing food for deer herds, while tigers hunt the deer. At the same time, due to insufficient rainfall this year, the forest’s waterholes are shrinking.

1. In a food chain, what does the direction of the arrow represent? Briefly describe its significance.

Answer:
The arrow direction represents energy flow. Its significance is to show the logical sequence of energy moving from the 'eaten' organism into the 'predator'.

2. When wolf packs and foxes both hunt rabbits in the forest, what kind of relationship exists between them?

Answer:
They have a 'competition' relationship because they are both competing for the same limited food resource—rabbits.

3. List three roles in a simple food chain and explain who is the 'producer'.

Answer:
For example, 'grass → grasshopper → frog'. In this case, 'grass' is the producer because it can make its own nutrients.

4. Why do organisms constantly need to obtain energy from food? What is its fundamental importance for sustaining life?

Answer:
Organisms need energy for growth, movement, repairing damaged tissues, and maintaining basic life functions such as breathing.

5. In the relationship between 'grass, deer, tiger', identify who is the predator and who is the prey.

Answer:
In the deer-tiger relationship, the tiger is the predator and the deer is the prey; in the grass-deer relationship, the deer is the predator (herbivore), and the grass is the prey.

6. How does competition between organisms change when survival resources become extremely scarce?

Answer:
Competition becomes much more intense. This may lead to reduced population numbers, or even force certain species to migrate or face survival threats.