AQA Biology 4.7.4.3 · Triple only
Transfer of biomass
Where the mass of a meal goes, why about 90% never reaches the next level, and how to turn two biomass values into an efficiency.
Triple Science · Higher tier
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A big dinner.
You eat a large dinner, but the next morning you have not gained a dinner’s weight.
If you had to guess, did most of that mass leave your body, or did it turn into muscle and fat?
Where the biomass goes
1000 g of grass into a rabbit.
Producers are mostly plants and algae which transfer about 1% of the incident energy from light for photosynthesis. Then only approximately 10% of the biomass from each trophic level is transferred to the level above it. Follow 1000 g of grass. The split is illustrative; it varies between organisms.
Which of these is egested rather than excreted?
Pick one.
Less biomass at each level supports fewer organisms, so food chains rarely go beyond four or five levels. Farmers use this: limiting an animal’s movement means less of its food is used in respiration, so more becomes body mass.
Equation · efficiency of biomass transfer
Efficiency is the biomass that reaches the next level as a fraction of the biomass at this level. Both values must be in the same unit. Tap the quantity you want to find.
Equation
Efficiency of biomass transfer
Side by side: multiply.
One over the other: divide.
Tap the quantity you want to find.
Written out
efficiency = biomass at the next level ÷ biomass at this level
- B2
- biomass at the next level
- g/m², kg/m² or kg (same unit for both)
- E
- efficiency (as a decimal)
- × 100 for %
- B1
- biomass at this level
- g/m², kg/m² or kg (same unit for both)
The triangle gives the efficiency as a decimal (or a fraction). Turning it into a percentage is its own line:
efficiency (%) = decimal × 100
Always divide the next level by this level. An answer over 100% means you divided the bigger number by the smaller: impossible, so turn it round.
Think again · over 100%?
“Divide the bigger number by the smaller.”
Your call
ChooseGrass 4000 g/m², rabbits 320 g/m². A pupil writes efficiency = (4000 ÷ 320) × 100 = 1250%. What has gone wrong?
Sort
Egested or excreted?
Place each loss.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Calculate
- Efficiency as a percentage or a fraction; biomass transferred; two transfers in a row.
- Explain
- How biomass is lost between trophic levels, and the effect on numbers at each level.
- Describe
- The 1% and the 10%.
Key fact
Only about 10% of the biomass at one trophic level reaches the next. The rest leaves as faeces (egested), as carbon dioxide and water from respiration, and as urea and water in urine. Efficiency = next level ÷ this level, then × 100.
Key note · AQA 4.7.4.3 (Biology only)
Transfer of biomass
- Producers are mostly plants and algae which transfer about 1% of the incident energy from light for photosynthesis.
- Only approximately 10% of the biomass from each trophic level is transferred to the level above it.
- Losses: not all the ingested material is absorbed, some is egested as faeces; some absorbed material is lost as waste, such as carbon dioxide and water in respiration and water and urea in urine. Large amounts of glucose are used in respiration.
- Efficiency = biomass at the next level ÷ biomass at this level, as a fraction or × 100 as a percentage. Match the units first. Over 100% is impossible.
- Two transfers: multiply the efficiencies (10% of 10% is 1%). Less biomass at each level supports fewer organisms, so chains are short.
Photograph this card. Tomorrow, cover it and say each line first.
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Getting an efficiency over 100%?
All biomass values are made up round numbers for practice.