Food Chain, Food Web and Pyramid of Numbers (Leaving Cert Biology): Revision Notes
📚 Revision Notes
Food Chain, Food Web and Pyramid of Numbers
Food Chain
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Food chain: a sequence of organisms where each organism is eaten by the next one in the chain. Energy is lost at each stage.
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Trophic level: feeding stage in a food chain.
- A food chain is a sequence of organisms where each organism is eaten by the next one in the chain. Energy is lost at each stage.
- Each feeding stage in a food chain is called a trophic level.
- Food chains are usually short as lots of energy is lost at each level. About 90% of energy is lost at each feeding level.
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Exam focus: You need to know a food chain with 4+ trophic levels for the exam.
Tip: Exam Question! Why are food chains short?
- Energy decreases at each trophic level, limiting the chain's length.
- Only 10% of energy is passed to the next level.
- The other 90% is used by organisms for activities (e.g., flying, running) or lost as heat.
Food Web
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Food web: a series of interconnected food chains.
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Exam focus: Include at least 9 organisms in your food web.
Pyramid of Numbers
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Pyramid of numbers: a diagram that shows the numbers of organisms at each trophic level in a food chain.
- The length of each bar represents the relative number of organisms.
- The size of organisms usually increases as you move up the pyramid.
Standard Pyramid of Numbers:
Inverted Pyramid of Numbers:
Limitations of the Pyramid of Numbers
- Individual organism size is not taken into account.
- The pyramid may not be to scale because the numbers can be very large (e.g., millions of bacteria on one ash tree).
Niche
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Niche: the functional role of an organism in an ecosystem or habitat.
- Each organism is adapted to occupy a unique niche.
- No two organisms can occupy the same niche without competing.
- Example: Swallows and bats both eat insects. Swallows feed by day and bats feed by night. Therefore, they occupy different food niches.