19.1.4Organisms and their Environment
Pyramids of Energy — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 6 parts Lesson 9 of 9 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 6Energy Loss Between Levels
The Sun is the original source of energy, but only a small part of it passes on from one trophic level to the next.
Not all eaten
- Not all eaten Some parts of an organism, such as roots or bones, are not eaten, so the energy stored in them is not transferred.
Not all digested
- Not all digested Material that is not digested leaves the body as faeces, which then supplies decomposers rather than the next consumer.
Respiration
- Respiration Energy is released in respiration and used for movement, so much of it is eventually lost as heat to the surroundings.
Excretion
- Excretion Metabolic waste such as urine removes some of the chemical energy from the organism.
About 10%
- About 10% Only around 10% of the energy at one trophic level is available to the next, though the figure varies.
Part 2 of 6Consequences
Consequences
Short food chains
- Short food chains Rapid loss of energy means food chains rarely have more than five links, as not enough energy remains for another level.
Pyramid shape
- Pyramid shape A pyramid of energy is always a true pyramid because energy decreases at each level.
Human diets
- Human diets Eating plants directly gives humans more of the energy captured by the crop than eating animals that were fed on the crop.
Land use
- Land use Producing plant food needs less land per person than producing meat, which affects choices in food supply.
Part 3 of 6Energy Compared With Biomass
Energy Compared With Biomass
Highlights losses
- Highlights losses A pyramid of energy shows directly how much energy is lost at each trophic level.
Fairer comparison
- Fairer comparison Different organisms store different amounts of energy per gram, and energy pyramids account for this.
Units
- Units Energy values are normally given per unit area per year, such as kJ per m² per year, so that data are comparable.
Drawback
- Drawback Measuring energy content needs special equipment, so it is harder to collect the data than counts or masses.
| Trophic level | Energy (kJ per m² per year) |
|---|---|
| Producers | 20 000 |
| Primary consumers | 2 000 |
| Secondary consumers | 200 |
| Tertiary consumers | 20 |
Part 4 of 6Calculating Transfer
1
Find the energy at the lower trophic level and at the higher trophic level from the data given.
2
Divide the energy at the higher level by the energy at the lower level.
3
Multiply by 100 to express the answer as a percentage of energy transferred.
4
Subtract from 100 if the question asks for the percentage lost.
Part 5 of 6Worked Example
Question
- A grass crop stores 8000 kJ per m² per year.
- The animals feeding on it store 720 kJ per m² per year.
- Calculate the percentage of energy transferred, and the percentage lost.
- Percentage transferred = 720 ÷ 8000 × 100 = 9%.
- Percentage lost = 100 − 9 = 91%.
Answer 9% of the energy is transferred to the primary consumers and 91% is lost.
Part 6 of 6Exam Checklist & Tips
19.1.4 – Key Points for the Exam
- Energy transfer The movement of energy from one trophic level to the next.
- Pyramid of energy A diagram showing the energy stored at each trophic level.
- Respiration The release of energy from food in cells.
- Decomposer An organism that gets energy from dead or waste organic material.
- Efficiency The percentage of energy passed on compared with that received.
Common Mistakes
- Saying energy is destroyed, when it is transferred to the surroundings, mostly as heat.
- Writing that 10% of the organisms, rather than 10% of the energy, is passed on.
- Forgetting to give units for energy, such as kJ per m² per year.
- Drawing an energy pyramid with any level wider than the one below it.
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