What is Biomass Energy?

Biomass energy is one of the most misunderstood topics in the curriculum. Is it a biological measurement? Is it a renewable fuel? In reality, it is both.

In 2026, examiners are looking for students who can bridge the gap between how biomass is produced in nature and how it is harnessed by humans for electricity and heat.

What is Biomass?

In a biological context, biomass is the total mass of living material in a specific area at a specific time. It represents the “chemical energy” stored within an organism.

The “Dry Mass” Gold Standard

For your A Level Biology practicals, remember:

• Wet Mass: Unreliable because water content varies (e.g., a plant after a rainstorm vs. a drought).
• Dry Mass: The mass of an organism after all water has been removed.
• Measurement Process: Scientists heat samples in a low-temperature oven (~80°C) and weigh them repeatedly until the mass becomes constant.

Biomass Energy in Ecosystems

Every calorie of energy in biomass originally came from the sun. Plants (producers) convert light energy into chemical energy through photosynthesis.

Pyramids of Biomass and Efficiency

In a food chain, biomass is lost at every level. On average, only 10% is passed on.

• Where does the energy go? It is lost through respiration (heat), movement, excretion (feces/urea), and parts that are not eaten (roots/bones).
• The 2025 Math Requirement: You must be able to calculate efficiency:
  $\text{Efficiency}=\frac{\text{Energy available after transfer}}{\text{Energy available before transfer}}\times 100$

Biomass as a Renewable Energy Source

Beyond ecosystems, Biomass Energy refers to the fuel we create from organic materials. In 2025, this is a critical part of the UK’s and the world’s “Net Zero” strategy.

The Three Main Types of Biomass Fuel:

1. Solid Biomass: Burning wood, straw, or poultry litter directly to produce heat or steam for electricity.
2. Biofuels (Liquid):
   • Bioethanol: Created by fermenting sugar/corn crops.
   • Biodiesel: Created from vegetable oils or recycled cooking grease.
3. Biogas (Gas): Produced via Anaerobic Digestion. Bacteria break down sewage or animal manure in the absence of oxygen to produce Methane.

The Sustainability Debate: Is it Truly “Carbon Neutral”?

Exam boards like AQA and Edexcel Geography focus heavily on the evaluation of biomass.

The Pros:

• Carbon Neutrality (Theory): The $C{O}_2$ released when burning the fuel is equal to the $C{O}_2$ absorbed by the plant while it was growing.
• Waste Reduction: It turns landfill waste (sewage/food scraps) into useful electricity.

The Cons (The 2025 “Grade 9” Perspective):

• Carbon Debt: Burning a tree takes minutes, but it takes 30–50 years for a new tree to grow and “re-absorb” that carbon. This creates a temporary spike in global warming.
• Food vs. Fuel: In many countries, land that should be used to grow food is being used to grow “energy crops” (like maize for biogas), which can drive up food prices.
• Biodiversity Loss: Monoculture plantations (growing only one type of tree for fuel) destroy natural habitats.

How to Measure the Energy Content (Calorimetry)

If an exam question asks, “How do we know how much energy is in this wood chip?”, the answer is Calorimetry.

• Process: A known mass of dry biomass is burned in a Bomb Calorimeter.
• Measurement: The heat released from the burning biomass increases the temperature of a known volume of water.
• Calculation: Because we know the “specific heat capacity” of water, we can calculate exactly how many Joules of energy were in the biomass based on the temperature rise.

Biomass Revision Cheat Sheet (GCSE & A Level)

Topic & Exam Level	Sample Exam Question	Model Answer / Key Marking Points
Energy Loss (GCSE Biology)	Explain why the biomass of the top predator in a food chain is much less than the biomass of the producers.	• Not all parts of the organism are eaten (e.g., bones, roots). • Biomass is lost as waste/excretion (e.g., urea, feces). • Energy is used for respiration to release heat. • Energy is used for movement or keeping warm.
Efficiency Calculation (GCSE Science)	Calculate the efficiency of biomass transfer from a primary consumer (1500kg) to a secondary consumer (120kg).	• Formula: $\frac{\text{biomass in higher level}}{\text{biomass in lower level}}\times 100$ • $\frac{120}{1500}\times 100=\mathbf{8}\mathbf{\%}$
Dry Mass Method (A Level Biology)	Describe how a scientist could determine the dry mass of a sample of plant material.	• Heat the sample in an oven at a low temperature (to prevent burning). • Weigh and reheat the sample at regular intervals. • Continue until the mass becomes constant (ensures all water is removed).
Renewable Energy (GCSE Physics/Geog)	Evaluate the use of biomass as a replacement for fossil fuels.	• Pros: Renewable; carbon-neutral (CO₂ absorbed during growth equals CO₂ released when burned). • Cons: Large areas of land needed (crops vs. food); may lead to deforestation; lower energy density than fossil fuels.
Calorimetry (A Level Biology)	How can a bomb calorimeter be used to estimate the chemical energy stored in dry biomass?	• A known mass of dry biomass is burned in pure oxygen. • The heat released increases the temperature of a known volume of water. • Use 𝑄=𝑚𝑐Δ𝑇 to calculate energy based on the temperature rise.

Pro-Tip for 2026 Exams:

When writing about biomass energy, never say it “does not produce $C{O}_2$. It does produce $C{O}_2$when burned.

The correct phrasing is that it is “Carbon Neutral” because it recycles atmospheric carbon rather than adding “new” carbon from fossil fuel reserves.

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