Food Chain
A food chain is a linear sequence showing how energy and matter are transferred from one organism to the next through feeding relationships, beginning with a producer and ending with a top predator or decomposer. Each link in the chain represents a trophic level, and only about 10% of the energy from one level passes to the next due to metabolic losses. Food chains illustrate the flow of energy through an ecosystem and help predict the effects of removing or adding species.
Key Formula
Energy at next level = Energy at current level × 0.10 (10% rule)
LaTeX: \text{Energy transferred} = \text{Energy at level } n \times 0.10
| Symbol | Meaning | Unit |
|---|---|---|
| 0.10 | Ecological efficiency (approximately 10%) | dimensionless |
| n | Current trophic level number | dimensionless |
Worked Example
Problem
A grassland food chain starts with grass containing 10,000 kJ of energy. Applying the 10% rule, how much energy is available to a hawk that feeds on snakes that eat frogs that eat grasshoppers that eat grass?
Solution
Trophic level 1 (Grass): 10,000 kJ Trophic level 2 (Grasshoppers): 10,000 × 0.10 = 1,000 kJ Trophic level 3 (Frogs): 1,000 × 0.10 = 100 kJ Trophic level 4 (Snakes): 100 × 0.10 = 10 kJ Trophic level 5 (Hawk): 10 × 0.10 = 1 kJ
Answer
1 kJ available to the hawk — only 0.01% of the original energy
Example Grassland Food Chain
| Trophic Level | Organism | Role | Energy Available (kJ) |
|---|---|---|---|
| Level 1 | Grass | Producer (autotroph) | 10,000 |
| Level 2 | Grasshopper | Primary consumer (herbivore) | 1,000 |
| Level 3 | Frog | Secondary consumer (carnivore) | 100 |
| Level 4 | Snake | Tertiary consumer (carnivore) | 10 |
| Level 5 | Hawk | Apex predator (quaternary consumer) | 1 |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Food Web
A food web is a complex network of interconnected food chains within an ecosystem, showing all the feeding relationships among organisms and the multiple pathways through which energy and nutrients flow. Unlike a simple linear food chain, a food web more accurately represents real ecosystems where most organisms eat more than one type of food and are eaten by more than one predator. Food webs are used to model the cascading effects that result from changes in species populations, such as the removal of a keystone species.
Trophic Level
A trophic level is a position in a food chain or food web occupied by organisms that obtain their energy from the same source and in the same number of steps from the primary producers. Level 1 consists of producers (plants), level 2 of primary consumers (herbivores), level 3 of secondary consumers, and so on. Due to the 10% energy transfer rule, food chains rarely extend beyond four or five trophic levels.
Primary Producer
A primary producer is an organism that synthesises its own food from inorganic compounds using an external energy source, forming the base of the food chain and supplying energy and organic matter to all other trophic levels. Most primary producers are photosynthetic — using sunlight to convert CO₂ and water into glucose — but chemosynthetic producers in deep-sea vents use chemical energy instead. Without primary producers, no ecosystem could sustain higher-order consumers or decomposers.
The term food chain was introduced by South African zoologist Charles Elton in his 1927 book "Animal Ecology." Chain from Old English cæne, via Old French chaîne, from Latin catena (a chain of links), metaphorically applied to feeding sequences.