Biomass Transfers through Ecosystems 🌾🐄📊

Why is biomass measured as dry mass rather than fresh mass?

• The water content of organisms varies significantly and contains no chemical energy. Dry mass allows for a fair comparison of the biological material present.

What is Biomass?

• Biomass is the mass of living material (e.g., proteins, carbohydrates) in an organism or area. It can be equated to the chemical energy stored in the organism.

How does biomass move up a food chain?

• \text{Producers}\rightarrow\text{Primary Consumers}\rightarrow\text{Secondary Consumers}

• However biomass is lost at each stage.

Why does biomass in each stage in the food chain get lost at each stage?

• Biomass lost as faeces.

• Energy from respiration is transferred to the surroundings.

Describe the method used to determine the dry mass of an organism.

• Kill the organism.

• Heat in an oven (at approx 80°C).

• Weigh periodically until the mass is constant (all water has evaporated).

State the formula for the efficiency of biomass transfer.

• \text{Efficiency} (\%)= \left( \frac{\text{Biomass transferred to next level}}{\text{Biomass intake at current level}} \right) \times 100

Why do producers only convert a small percentage (1-3%) of sunlight into biomass?

• Light is reflected off the leaf.

• Light passes through the leaf (transmission) without hitting chloroplasts.

• Light is of the wrong wavelength (e.g., green light is reflected).

List three reasons why biomass is lost between Primary Consumers (herbivores) and Secondary Consumers (carnivores).

• Respiration: Energy lost as heat (movement/metabolic heat).

• Egestion: Not all food is digested (e.g., cellulose/bones/hair) and is lost in faeces.

• Excretion: Energy lost in urine (urea).

What is Gross Primary Production (GPP)?

• The rate at which plants convert light energy into chemical energy (biomass) through photosynthesis.

How do Herbicides increase the efficiency of energy transfer in crop production?

• They kill weeds, removing interspecific competition. This means the crop gets more light, water, and nutrients, increasing its rate of growth (Net Primary Production).

What is the formula linking Net Primary Production (NPP), Gross Primary Production (GPP), and Respiration (R)?

• \text{NPP} = \text{GPP} - R

How does intensive farming (factory farming) of livestock improve secondary productivity?

• Restricted movement: Reduces energy lost to muscle contraction/respiration.

• Controlled temperature: Reduces energy lost to maintaining body heat.

• High-protein feed: Maximises growth.

How do Fungicides increase biomass in crops?

• They kill fungal infections (like blight/rot) which would otherwise damage leaves (reducing photosynthesis) or consume the plant's stored nutrients.

Explain why food chains rarely have more than four or five trophic levels. (3 marks)

• Energy/biomass is lost at each trophic level (due to respiration/excretion/inedible parts) (1).

• Only a small proportion (approx 10%) is transferred to the next level (1).

• By the 4th/5th level, there is insufficient energy/biomass remaining to support a viable population of predators (1).

Calculate the efficiency of biomass transfer if a cow eats $2500kg of grass and increases its own biomass by 100kg. (2 marks)

Formula:

• \frac{\text{Biomass Transferred}}{\text{Biomass Intake}} \times 100

• \frac{100}{2500} \times 100 = \mathbf{4\%}

Farmers often remove hedges to create larger fields (monoculture). Explain the effect this has on the food web and biomass transfer. (3 marks)

• Removing hedges destroys habitats, reducing biodiversity (1).

• This removes natural predators of pests (e.g., beetles/birds), potentially increasing pest populations (1).

• However, it allows for easier machinery use and removes competition for the crop, aiming to increase the yield/biomass of the single crop species for human consumption (1).