Energy Flow Explained — Food Chain, Food Web, Trophic Levels & Pyramid (JAMB/WAEC Biology)

Energy flow describes how energy moves through an ecosystem, starting from the sun, passing through producers and consumers, and being lost as heat at each stage. 

This topic covers four connected ideas – food chains, food webs, trophic levels, and ecological pyramids, and it’s a recurring favorite in JAMB and WAEC Biology, often tested through diagrams and “identify the trophic level” questions. This lesson explains all four with clear examples.

Quick takeaways

• A food chain shows a single, straight-line path of energy transfer; a food web shows multiple interconnected food chains.
• Trophic levels classify organisms by their feeding position: producers, primary consumers, secondary consumers, and so on.
• Energy decreases at each trophic level – typically only about 10% is passed on, with the rest lost mainly as heat.
• Ecological pyramids (of numbers, biomass, and energy) visually represent this decrease, usually getting narrower toward the top.
• Exam questions often ask you to identify a trophic level from a food chain or explain why energy decreases up the chain.

Timestamps

• 0:00 Introduction
• 0:44 Food Chain
• 5:35 Food Web
• 7:43 Trophic Levels
• 8:12 Pyramid of Energy
• 10:01 Pyramid of Numbers
• 11:55 Summary

What is a food chain?

A food chain is a straight-line sequence showing how energy passes from one organism to another, starting with a producer and moving through a series of consumers. For example: grass → grasshopper → frog → snake → hawk. Each arrow represents the direction of energy flow, from the organism being eaten to the one eating it.

What is a food web, and how is it different from a food chain?

A food web is a network of multiple, interconnected food chains within an ecosystem, showing that most organisms don’t rely on just one food source. While a food chain gives a single simplified path, a food web reflects the more realistic, complex feeding relationships in nature – a single producer might feed several different primary consumers, and a single predator might eat several different prey species.

What are trophic levels?

Trophic levels classify organisms in a food chain based on their feeding position:

1. Producers – organisms that make their own food, usually through photosynthesis (e.g., green plants)
2. Primary consumers – herbivores that eat producers directly
3. Secondary consumers – carnivores that eat primary consumers
4. Tertiary consumers – carnivores that eat secondary consumers
5. Decomposers – organisms that break down dead organic matter, recycling nutrients back into the ecosystem

Every organism in a food chain occupies one of these levels, and exam questions frequently ask you to identify the trophic level of a named organism within a given chain.

Why does energy decrease at each trophic level?

Energy decreases as it moves up a food chain because a large portion is lost at each transfer, mainly as heat through respiration, but also through movement, undigested material, and other life processes. On average, only about 10% of the energy at one trophic level is passed on to the next – this is often called the “ten percent rule.” 

This is also why food chains rarely extend beyond four or five trophic levels; there simply isn’t enough energy left to support another level.

What is an ecological pyramid, and what does it show?

An ecological pyramid is a graphical representation of the relationship between organisms at different trophic levels, and it usually narrows toward the top because both energy and biomass decrease at higher levels. There are three main types:

1. Pyramid of numbers – shows the number of organisms at each trophic level
2. Pyramid of biomass – shows the total mass of organisms at each trophic level
3. Pyramid of energy – shows the amount of energy available at each trophic level (always upright, unlike the other two, which can occasionally be irregular in shape)

Common mistakes students make with this topic

• Confusing a food chain (single path) with a food web (interconnected network)
• Forgetting that decomposers, not just consumers, play a critical role in recycling nutrients
• Assuming all three types of ecological pyramids always look the same shape – only the pyramid of energy is always upright
• Misidentifying the trophic level of an organism when a food chain has more than three or four steps

Frequently asked questions

Q: What is the difference between a food chain and a food web? A food chain shows a single, straight-line sequence of energy transfer between organisms, while a food web shows multiple interconnected food chains, reflecting the more complex feeding relationships that exist in real ecosystems.

Q: What are the main trophic levels in a food chain? The main trophic levels are producers, primary consumers, secondary consumers, tertiary consumers, and decomposers, each defined by their feeding position in the chain.

Q: Why is only about 10% of energy passed from one trophic level to the next? Most energy is lost as heat through respiration, along with smaller losses through movement and undigested material, leaving only a small fraction available to be passed on to the next trophic level.

Q: Which type of ecological pyramid is always upright? The pyramid of energy is always upright, since energy consistently decreases at each successive trophic level, unlike pyramids of numbers or biomass, which can occasionally be irregular.

Want to see how human activity disrupts this balance? Read our Human and His Environment lesson.

This is one topic from our full WAEC & JAMB Biology course — see everything covered →