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Unlock This CourseEvery living thing needs energy to survive, grow and reproduce. In nature, energy flows from one organism to another through feeding relationships called food chains. Think of a food chain as nature's way of passing energy around - like a relay race where the baton is energy!
Food chains show us who eats whom in an ecosystem and help us understand how energy moves through different levels of life. From tiny algae to massive predators, every organism has a role to play in this energy transfer system.
Key Definitions:
All food chains start with producers - usually green plants, algae, or some bacteria. These amazing organisms capture energy from sunlight and convert it into food through photosynthesis. They're called producers because they literally produce their own food from simple ingredients like carbon dioxide and water. Without producers, no other life could exist!
Constructing a food chain is like building a tower - you need to start with a solid foundation and add each level carefully. Let's explore how to build food chains correctly and what each level represents.
Most food chains have between three to four levels, each representing a different feeding position. Understanding these levels is crucial for constructing accurate food chains.
Green plants, algae and some bacteria that make their own food through photosynthesis. Examples: grass, oak trees, seaweed, phytoplankton.
Herbivores that eat producers. They're the first consumers in the chain. Examples: rabbits, caterpillars, zebras, krill.
Carnivores that eat primary consumers. Examples: foxes, birds, small fish, spiders.
Top predators that eat secondary consumers. Examples: lions, eagles, sharks, wolves. These are often called apex predators.
In a typical British oak woodland: Oak tree → Caterpillar → Blue tit → Sparrowhawk. This shows energy flowing from producer (oak) through three consumer levels. The oak provides leaves for caterpillars, which are eaten by blue tits, which in turn become prey for sparrowhawks. Each arrow shows the direction of energy flow.
Building accurate food chains requires following specific rules. Getting these right is essential for understanding how ecosystems work and for your iGCSE exams!
The most common mistake students make is getting the arrows wrong. Remember: arrows show the direction of energy flow, not who eats whom!
Grass → Rabbit → Fox. The arrow points FROM the food TO the feeder. Energy flows from grass to rabbit to fox. Think of it as 'energy goes to' rather than 'eats'.
You might wonder why food chains don't go on forever. There are important scientific reasons why most food chains have only 3-4 levels.
As energy moves up each level of a food chain, about 90% is lost as heat, movement and waste. Only about 10% passes to the next level. This means there's less and less energy available at higher levels.
If grass captures 1000 units of energy from sunlight, rabbits only get 100 units, foxes get 10 units and a fox predator would only get 1 unit. This explains why there are fewer predators than prey in ecosystems.
North Sea marine chain: Phytoplankton → Zooplankton → Herring → Seal → Killer whale. This five-level chain is unusual and only possible in highly productive marine environments. The phytoplankton are microscopic producers that support this entire chain through photosynthesis in surface waters.
While food chains show simple linear feeding relationships, real ecosystems are much more complex. Most organisms eat more than one type of food and are eaten by more than one predator.
Food chains are like single roads showing one route through an ecosystem, while food webs are like complex motorway systems showing all possible routes.
A fox doesn't just eat rabbits - it might also eat birds, insects and berries. Similarly, rabbits aren't just eaten by foxes - they're also prey for hawks, weasels and other predators. Food webs show these interconnected relationships.
While not part of the main food chain, decomposers play a crucial role in ecosystems by breaking down dead organisms and waste, returning nutrients to the soil.
Bacteria and fungi are nature's recyclers. They break down dead plants and animals, releasing nutrients back into the ecosystem for producers to use again.
Now let's put everything together and practice building food chains from different ecosystems.
Lettuce → Slug → Thrush → Cat. This shows energy flowing from producer (lettuce) through three consumer levels in a typical British garden.
Pondweed → Water flea → Stickleback → Pike. Aquatic food chains often have similar structures to terrestrial ones.
Beech tree → Aphid → Ladybird → Spider → Bird. Some chains can have more levels when there's abundant energy at the base.
When constructing food chains in exams, always start by identifying the producer (usually a green plant), then work your way up through the consumers. Check your arrows point in the direction of energy flow and make sure each organism can realistically eat the one before it in the chain.