Energy and ecosystems

What is Biomass?

Biomass refers to the total mass of living material in a specific area or volume, expressed as either carbon mass or dry mass.

It represents the chemical energy stored in organisms and forms the foundation of energy flow in ecosystems.

Biomass can be measured as dry mass (mass of tissue without water) per given area.

The chemical energy in dry biomass can be estimated using calorimetry, where:

• A sample is burned in a calorimeter.

• Heat released heats a known volume of water, and the temperature change is used to calculate energy content.

Food Chains:

• Show linear energy flow from producers to consumers.

• Simplify complex interactions but do not show the full picture.

Food Webs:

• Illustrate interconnected feeding relationships in an ecosystem.

• Highlight how energy flows through multiple pathways.

Primary production

Primary productivity refers to the rate of energy production by producers (plants).

It is measured in biomass per unit area per year (e.g., kJ m⁻² year⁻¹).

Gross Primary Production (GPP) is the total amount of chemical energy fixed by plants via photosynthesis in a given area or volume.

It forms the energy basis for all organisms in the ecosystem.

Net Primary Production (NPP) is the energy remaining in plant biomass after respiratory losses are accounted for.

Energy is lost as plants respire (R) for their metabolic processes.

Formula: 

NPP = GPP− R

Significance: NPP is the energy available for:

• Plant growth and reproduction.

• Transfer to other trophic levels, such as herbivores and decomposers.

Secondary production

Secondary Productivity refers to the rate of energy production by consumers.

It rreflects energy stored in animal biomass after losses through respiration and excretion.

Net Production of Consumers (N) is the energy available to animals after accounting for energy losses.

Formula: 

N = I − (F + R)

Where:

• I: Energy ingested through food.

• F: Energy lost in feces and urine.

• R: Energy lost due to respiration.

Factors affecting energy transfer

Only a small percentage of energy is transferred from one trophic level to the next:

Calculation of Efficiency: 

At the Producer Level:

• Not all sunlight is captured:

  • Light is reflected, absorbed by the atmosphere, or of non-absorbed wavelengths.

  • Environmental factors (e.g., low temperatures, water availability) can limit photosynthesis.

At the Consumer Level:

• Not all parts of the food are consumed (e.g., bones, cellulose).

• Energy losses occur through:

  • Digestion and egestion (excretion of undigested material).

  • Respiration and movement.

  • Heat loss, especially in warm-blooded animals.

Agricultural ecosystems

Agricultural ecosystems aim to maximize energy transfer to humans.

They often involve monocultures (single-species crops) and high-input farming methods.

Methods to maximise productivity for crops:

• Remove competitors like weeds and pests.

• Apply fertilizers to replenish nutrients.

• Irrigation to maintain water supply.

Methods to maximise productivity for livestock:

• Restrict movement to reduce energy loss.

• Maintain warm environments to minimize heat loss.

• Use selective breeding for efficiency.

Environmental and Ethical Concerns:

• Environmental Impacts:

  • Habitat destruction, deforestation, and loss of biodiversity.

  • Pollution from fertilizers, pesticides, and concentrated waste.

• Ethical Issues:

  • Animal welfare concerns (e.g., cramped conditions, overuse of antibiotics).

  • Disease spread in high-density populations.

  • Climate impact from methane emissions.

Definitions