Ecosystem Productivity
This term describes the total rate at which primary producers convert solar energy into chemical energy through photosynthesis—often thought of as an ecosystem's "gross income".
What is Gross Primary Productivity (GPP)?
This percentage represents the average amount of energy stored as biomass at one trophic level that is successfully transferred to the next.
What is 10%?
This fundamental law of physics states that energy cannot be created or destroyed, only transformed from one form to another.
What is the First Law of Thermodynamics?
Bacteria, fungi, and detritivores perform this critical function by breaking down dead organic matter.
Organisms that produce their own organic food from inorganic carbon sources are broadly known by this term.
What are Autotrophs?
Expressed as a simple equation, this represents the net chemical energy remaining in plant tissues available to herbivores after accounting for plant respiration (R)
What is NPP = GPP - R?
If primary producers in a grassland ecosystem store 10,000 J of energy in their biomass, calculate the amount of energy available to the tertiary consumers.
What is 10 J?
Primary producer: 10,000 J
Primary Consumer: 1,000 J
Secondary Consumer: 100 J
Tertiary Consumer: 10 J
Unlike matter, which continuously cycles through decomposers, energy moves through an ecosystem in this specific manner.
What is one direction (unidirectional flow)?
Name two of the primary inorganic nutrients released back into the soil and air during decomposition.
What are Nitrogen, Phosphorus, or Carbon?
Unlike plants that use sunlight, deep-sea hydrothermal vent bacteria acquire energy from inorganic molecules like hydrogen sulfide using this metabolic pathway.
What is chemosynthesis?
Name two ecosystems that typically exhibit high Net Primary Productivity due to abundant warm sunlight, water, and nutrients.
Answer: What are Tropical Rainforests, Estuaries, or Coral Reefs?
TWO of the three primary reasons why 90% of energy is NOT transferred to the next trophic level.
What are Cellular Respiration/Heat Loss, Egested Waste (feces), and Uneaten Biomass (roots, bones, fur)?
According to the Second Law of Thermodynamics, every time energy is transformed or moved up a food chain, some energy is lost to the environment in this specific low-grade form.
What is heat?
Evaluate the following prompt
Decomposers bridge the gap between matter cycling and ecosystem energy flow.
Is this correct? explain why
This is correct. Decomposers release inorganic nutrients from dead biomass back to the soil/water, which autotrophs require to perform photosynthesis and generate new biomass (NPP)
Organisms like the Venus flytrap or Euglena that combine autotrophic and heterotrophic pathways depending on environmental conditions are classified as these.
What are Mixotrophs?
Temperate Deciduous Forest: A temperate forest has an NPP of 16,000 kcal/m²/yr. If plant respiration (R) accounts for 6,000 kcal/m²/yr, what is the Gross Primary Productivity (GPP) of this ecosystem?
What is GPP= 22,000?
Can a terrestrial ecosystem support a 6th or 7th trophic level? Explain why or why not.
Because energy decreases exponentially by ~90% at each tier, after 4–5 levels there is insufficient energy remaining to support a viable population of apex predators
Contrast the long-term behavior of carbon or nitrogen atoms in an ecosystem with the path of solar energy absorbed by a plant leaf.
Matter is recycled continuously through abiotic and biotic pools, whereas solar energy flows through trophic levels and is ultimately lost as heat to space?
Predict what would happen to an ecosystem's Net Primary Productivity (NPP) over time if all decomposers were suddenly removed by a chemical agent.
NPP would crash/drop to near zero because essential inorganic nutrients would remain locked in dead organic biomass, causing nutrient starvation for primary producers
State the Competitive Exclusion Principle and explain how diverse energy acquisition strategies help prevent it among species occupying the same niche.
What is Two species competing for the exact same limited resource cannot stably coexist. Distinct acquisition strategies (niche differentiation/resource partitioning) allow species to use different energy sources, reducing direct competition?
An agricultural field of corn has a GPP of 20,000 kcal/m²/yr. Scientists determine that the corn plants use 60% of their total captured energy for respiration (R).
a. Calculate the amount of energy lost to respiration (R).
b. Calculate the Net Primary Productivity (NPP) of the cornfield.
a. R = ________________________ kcal/m²/yr
b. NPP = ________________________ kcal/m²/yr
Connecting NPP to the 10% Energy Rule:
If a grassland ecosystem has an NPP of 2,000 kcal/m²/yr, approximately how much energy is available to be passed on to:
a. Primary Consumers (Herbivores)?
b. Secondary Consumers (Carnivores)?
4a) R= 12,000
4b) NPP= 8,000
5a) 200kcal
5b) 20kcal
Predict the ecological consequence on trophic biomass and population sizes if an agricultural region transitions from human consumption of grain (herbivory) to human consumption of grain-fed beef (carnivory).
Eating beef adds a trophic level, losing ~90% more energy to heat/respiration. This requires significantly more grain/land/water to support the same human population compared to direct grain consumption?
Evaluate the following student claim: An ecosystem can operate as a completely closed loop where 100% of the energy is reused forever without solar input.
Is this claim true or false? Use the laws of thermodynamics to explain.
The claim is false because the Second Law of Thermodynamics states that energy transformations are inefficient, constantly losing energy as heat. Without a continuous external energy source (the Sun), the ecosystem will run out of usable energy
Distinguish the structural difference in ecosystem dynamics between disrupting a primary consumer population versus disrupting a decomposer population.
Disrupting a primary consumer impacts specific upper trophic levels in energy flow, but disrupting decomposers halts nutrient cycling entirely, collapsing the foundational primary productivity (NPP) that supports all trophic levels
How would mixotrophy allow for an organism to have a competitive advantage over strict autotrophs and strict heterotrophs in fluctuating environments.
Mixotrophy allows the organism to switch metabolic pathways based on resource availability. During high light, it acts autotrophically to capture solar energy without spending energy on hunting; when light is limited, it acts heterotrophically to extract energy and nutrients from prey. This flexibility prevents competitive exclusion by allowing it to maintain net energy gain when pure autotrophs starve from lack of light and pure heterotrophs starve from prey shortages.