19.1Organisms and their Environment
Energy flow — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 17 parts Lesson 3 of 7 Unit quiz
Lesson summary
19.1 Energy flow — IGCSE BIOLOGY notes: Explain energy flow through ecosystems, pyramids of number, biomass and energy, and why energy transfer is inefficient.Source — the Sun is the principal source of energy input to biological systems.Forms — light energy from the Sun and chem…
- Pyramid of numbers
- Width of box
- Larger organisms
- Pyramid of biomass
- Advantage over numbers
- Pyramid of energy
Part 1 of 8Energy flow
1Source
- Source the Sun is the principal source of energy input to biological systems.
2Forms
- Forms light energy from the Sun and chemical energy in organisms.
3Direction
- Direction energy flows through organisms and is eventually transferred to the environment as heat.
4
Energy flows, while nutrients cycle.
Part 2 of 8Pyramids of numbers
Pyramid of numbers
Pyramid of numbers shows how many organisms are present at each level of a food chain.
Width of box
- Width of box the number of organisms at that level.
Shape
- Shape not always pyramid-shaped because the size of organisms matters, for example one large oak tree supports many insects.
Larger organisms
- Larger organisms generally there are fewer individuals.
Part 3 of 8Rules for drawing pyramids of numbers
Order
- Order producers at the bottom, then primary, secondary and tertiary consumers.
Labels
- Labels each bar is labelled with its trophic level.
Scale
- Scale drawn to scale if graph paper is provided.
Part 4 of 8Pyramids of biomass
Pyramid of biomass
Pyramid of biomass shows how much living matter is present at each trophic level.
Biomass
- Biomass often measured as dry mass, once water is removed.
Shape
- Shape always pyramid-shaped because mass decreases up a food chain.
Advantage over numbers
- Advantage over numbers takes account of organism size, so gives a more accurate picture of living matter.
Energy
- Energy stored in biomass, so biomass approximates the energy available at each level.
Part 5 of 8Pyramids of energy
Pyramid of energy
Pyramid of energy shows the energy stored at each trophic level.
Always pyramid-shaped
- Always pyramid-shaped it is never inverted, because energy is lost at each stage.
Advantages
- Advantages highlights energy lost at each level and allows fair comparison, since organisms store different amounts of energy per unit biomass.
Part 6 of 8Why energy transfer is inefficient
Why energy transfer is inefficient
Respiration
- Respiration energy is released for movement and heat.
Excretion
- Excretion energy is lost in metabolic wastes such as urine.
Uneaten parts
- Uneaten parts roots of plants or bones of animals never enter the consumer.
Undigested waste
- Undigested waste faeces are removed and feed decomposers.
Transfer
- Transfer only about 10% of the energy at one level is available to the next.
Part 7 of 8Consequences of energy loss
Food chains
- Food chains rarely have more than five organisms, because the final consumer would need to eat huge numbers of organisms below.
More levels
- More levels the greater the number of trophic levels, the greater the energy loss.
Humans
- Humans it is more energy efficient to eat crop plants such as wheat than cattle fed on wheat.
Exceptions
- Exceptions animals often eat plants humans cannot, like grass, or plants too widely spread, like ocean algae.
Part 8 of 8More from the specification
Combustion energy of conventional fossil fuels
- Combustion energy of conventional fossil fuels burning coal, oil,
- and gas fossil fuels releases ancient trapped photosynthetic energy alongside carbon dioxide.
Unidirectional Energy Transfer from Sunlight
- Sunlight represents the principal initial source of biological energy;
- photosynthetic primary producers convert radiant solar energy into chemical energy stored within organic carbohydrates.
Thermodynamic Inefficiency Across Trophic Levels
- Approximately 90% of available energy is lost between consecutive trophic levels through cellular respiration, heat dissipation, incomplete digestion,
- and egestion, leaving only ~10% for incorporation into consumer biomass.
Limitations on Food Chain Length
- Due to persistent progressive thermodynamic energy losses, food chains rarely exceed four to five trophic levels before insufficient metabolic energy remains to sustain higher consumer populations.
Fossil fuel
- Fuel formed from long-dead organisms.
Population
- A group of organisms of one species in the same area at the same time.
Nitrogen
- Element in amino acids and nitrogenous bases.
Carbon
- Element with four valence electrons that forms the backbone of organic molecules.
Growth
- A permanent increase in size and dry mass.
Photosynthesis
- The process by which plants make carbohydrates from raw materials using energy from light.
Species
- A group of organisms that can reproduce to produce fertile offspring.
Microorganism
- A living organism so small that it can only be seen clearly with a microscope.
Bacteria
- Single-celled microorganisms, much smaller than plant or animal cells.
Key terms
| Term | Meaning |
|---|---|
| Producer | An organism that makes its own food, usually using sunlight. |
| Consumer | An organism that feeds on other organisms. |
| Trophic level | The feeding level of an organism in a chain. |
| Biomass | The mass of living matter, often dry mass. |
| Pyramid of energy | A diagram of energy stored at each trophic level. |
| Decomposer | An organism that feeds on dead or waste material. |
Avoid these mistakes
1
Saying pyramids of energy can be inverted — they cannot.
2
Saying energy is recycled — it is lost as heat.
3
Saying plants lose energy as urine or faeces — plants do not make these.
4
Saying all energy passes to the next level — only about 10% does.
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