Edexcel A Level (IAL) Biology -5.10 Energy & Biomass Transfers- Study Notes- New Syllabus

Efficiency of Biomass and Energy Transfer Between Trophic Levels

📌 Introduction

In a food chain, energy flows from one trophic level to the next (plants → herbivores → carnivores).
But not all the energy or biomass gets passed on. A lot is lost along the way.

🔹 Why Energy/Biomass Is Lost Between Levels

Before calculating efficiency, it helps to know where the energy disappears:

• Some energy is used in respiration (movement, metabolism).
• Some is lost as heat.
• Not all parts are eaten (bones, roots, bark).
• Not all eaten food is digested (lost as faeces).
• Biomass decreases as you move up trophic levels.
• That’s why pyramids of biomass always shrink.

🔹 Formula for Efficiency

Efficiency of Biomass Transfer (%)

Efficiency = Biomass transferred to next level Biomass available at previous level × 100

Efficiency of Energy Transfer (%)

Efficiency = Energy at next trophic level Energy at previous trophic level × 100

Both formulas are the same only the units change (kJ vs g of biomass).

🔹 Quick Example

If plants contain 5000 kJ and herbivores gain 500 kJ from them:

Efficiency = 500 5000 × 100 = 10 %

Meaning only 10 percent of the plant’s energy became herbivore biomass.

🔹 Why Efficiency Matters

• Explains why food chains are usually short (not enough energy to support many levels).
• Helps in farming to improve efficiency (e.g., warm sheds reduce heat loss).
• Shows how much energy humans get from different food sources.

📘 Summary Table

⚡ Quick Recap
Only a small amount of energy moves to the next trophic level.
Use the same percentage formula for biomass or energy.
Most loss happens via respiration and heat.
Food chains stay short because energy drops quickly.
Efficiency helps explain ecosystem structures and farming methods.