2.2 Energy and Biomass in Ecosystem

What is a trophic level?

A trophic level is a position in a food chain determined by how an organism obtains its energy, such as producers (T1), primary consumers (T2), etc.

What is a food chain?

A linear sequence showing the transfer of energy and matter through trophic levels as organisms eat and are eaten.

What is a food web?

A network of interconnected food chains showing how energy and matter flow through an ecosystem.

What do the arrows in a food chain represent?

The direction of energy flow, pointing toward where the energy goes.

What is energy transformation?

The conversion of one form of energy to another (e.g. light → chemical energy in photosynthesis).

What is matter transformation?

The conversion of substances (e.g. CO₂ and H₂O → glucose and O₂ in photosynthesis).

What are the laws of thermodynamics in ecology?

• 1st Law: Energy cannot be created or destroyed, only transformed.

• 2nd Law: Energy transformations are inefficient, and some energy is lost as heat.

What is photosynthesis?

The process where light energy is transformed into chemical energy as glucose using CO₂ and H₂O.
Equation:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

What is cellular respiration?

The process that releases energy from glucose by breaking it down with oxygen into CO₂ and H₂O.
Equation:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP + heat)

Why is heat produced in cellular respiration?

Because the process is not 100% efficient — some chemical energy is transformed into thermal energy and lost to the environment.

What is productivity?

The rate of creation of new biomass in an ecosystem per unit time.

What is gross productivity (GP)?

The total gain in biomass by an organism before energy losses from respiration.

What is net productivity (NP)?

The biomass remaining after energy losses from respiration.
Formula: NP = GP – R

What is primary productivity?

The rate at which producers (autotrophs) convert inorganic matter into organic biomass using an external energy source (usually sunlight).

What is gross primary productivity (GPP)?

The total biomass produced by primary producers per unit time.

What is net primary productivity (NPP)?

The biomass remaining after respiration losses in producers.
Formula: NPP = GPP – R
It represents the energy available to primary consumers.

What is secondary productivity?

The gain in biomass by consumers from feeding on other organisms.

What is gross secondary productivity (GSP)?

The biomass gained by consumers from food absorbed and assimilated, excluding faeces.
Formula: GSP = Food eaten – Faecal loss

What is net secondary productivity (NSP)?

The biomass remaining after accounting for respiration losses.
Formula: NSP = GSP – R

What is maximum sustainable yield (MSY)?

The maximum amount of biomass that can be harvested without reducing future yields, equivalent to net productivity.

Why are sustainable yields higher at lower trophic levels?

Due to the 2nd Law of Thermodynamics, less energy is lost between trophic levels at the bottom of the food chain, so more energy is available for harvest.

What are methods to measure primary productivity?

• Radioactive tracer method (C-14): Measures carbon fixation in biomass.

• Light-dark bottle technique: Measures O₂ production/consumption to estimate carbon uptake.

What does biomass represent?

The mass of living material or stored energy in an organism or trophic level.

What is a self-sustaining ecosystem?

A system where energy and matter cycles maintain themselves without external input, like aquaponics.