What is the key difference between how energy and nutrients move through an ecosystem?

The most fundamental difference is that energy flows, while nutrients cycle. Energy enters an ecosystem (usually from the sun), is transferred from one organism to another with significant loss as heat at each step, and does not get reused. Nutrients (matter), on the other hand, are finite and are continuously recycled within the ecosystem between living organisms and the non-living environment without being lost.

Why are food chains usually short, with only 4 or 5 trophic levels?

Food chains are limited in length due to the massive loss of energy at each trophic level, as described by the Second Law of Thermodynamics. Only about 10% of the energy from one level is incorporated into the next. After 4 or 5 transfers, there is simply not enough energy remaining to support a viable population at a higher trophic level.

Are decomposers part of the energy flow?

Yes, absolutely. Decomposers (like bacteria and fungi) obtain energy by breaking down dead organic matter from all trophic levels. In doing so, they respire, releasing heat energy, and are themselves consumed by other organisms. Crucially, they are also essential for nutrient cycling, as they return inorganic nutrients to the soil for producers to use again.

Is Energy flow, productivity and nutrient cycles (2.2) on IB ESS free to study?

Yes. The IB Environmental Systems and Societies course on MarkScheme is 100% free — including visual lessons, exam tips, flashcards, and criterion practice marking. No paywall for Energy flow, productivity and nutrient cycles.

How is IB Environmental Systems and Societies marked for Energy flow, productivity and nutrient cycles?

IB uses markbands and assessment criteria rather than Cambridge B1/M1/A1 codes. For Energy flow, productivity and nutrient cycles, examiners place your response in a level band against descriptors — our /mark tool scores criterion-by-criterion for IB ESS.

Energy flow, productivity and nutrient…

Revise Energy flow, productivity and nutrient cycles for IB Environmental Systems and Societies (2.2)

Looking for free IB Environmental Systems and Societies notes on Energy flow, productivity and nutrient cycles? This Standard Level lesson covers official syllabus point 2.2 on ESS SL. Use the visual steps, key terms, and quick checks below — then practise with IB criterion marking on Energy flow, productivity and nutrient cycles. Built for students searching "IB ESS 2.2", "Energy flow, productivity and nutrient cycles IB revision", or a free alternative to paid IB note sites.

Energy flow, productivity and nutrient cycles

Welcome to our exploration of Topic 2.2. In this lesson, we will unravel how ecosystems function by tracking the two most fundamental components: energy and matter. You will learn that energy flows in one direction, getting lost along the way, while essential chemical nutrients are endlessly recycled. Understanding these processes is crucial for analysing ecosystem health, stability, and the profound impacts of human activities.

BY THE END, YOU CAN…

1Explain the pathways of energy flow through ecosystems, including inputs, transfers, and outputs.
2Calculate and interpret values for gross and net productivity in producers and consumers.
3Describe the carbon and nitrogen cycles, identifying key storages, flows, and human impacts.
4Distinguish between the flow of energy and the cycling of matter in an ecosystem.

In simple terms

A friendly intro before the formal notes — no formulas yet.

The Ecosystem's Economy

Ecosystems run on an energy budget, where energy flows through once and is lost, while essential nutrients are constantly recycled. Productivity measures how efficiently organisms convert energy into biomass.

THINK OF IT LIKE…

Think of an ecosystem's energy flow like your personal finances. Your gross salary is the total energy captured (Gross Productivity). After you pay for your essential living costs like rent and food (Respiration), the money you have left to save or spend on growth is your net income (Net Productivity). You can't recycle the money you've spent, it's gone, just like energy is lost as heat.

1
First, identify the source of energy (usually the sun) and trace its path through different trophic levels, remembering that energy is lost at each step.
2
Next, distinguish between Gross Productivity (total energy assimilated) and Net Productivity (energy left for growth after respiration). Use the formulas NPP = GPP - R and NSP = GSP - R.
3
Then, analyse nutrient cycles like carbon and nitrogen by identifying the main storages (sinks) and the processes that move nutrients between them (flows or fluxes).
4
Finally, evaluate human impacts on these cycles, such as burning fossil fuels (carbon cycle) or using fertilisers (nitrogen cycle), and their consequences.

Explore the concept

Use the live diagram and synced steps — play it or tap a step card to walk through.

Key formulas

Tap any symbol to reveal exactly what it means and its units.

Net Primary Productivity (NPP) = Gross Primary Productivity (GPP) - Respiration (R)

Net Secondary Productivity (NSP) = Gross Secondary Productivity (GSP) - Respiration (R)

Full topic notes

Formal explanation with the rigour you need for the exam.

Energy Flow and the Laws of Thermodynamics

Energy in almost all ecosystems originates from the sun. This solar energy is captured by autotrophs (producers) and converted into chemical energy through photosynthesis. This energy is then transferred through the ecosystem as one organism consumes another. However, this flow is unidirectional and inefficient.

First Law of Thermodynamics: Energy can be transferred and transformed, but it cannot be created or destroyed. In ecosystems, this means solar energy is converted to chemical energy, which is then transferred between trophic levels.
Second Law of Thermodynamics: During any energy conversion, some energy is lost as heat, and the entropy (disorder) of the universe increases. This explains why energy transfers are inefficient (the '10% rule') and why food chains are limited in length. Energy is lost as heat during respiration at each trophic level.

Ecosystem Productivity

Productivity is the rate at which biomass is generated in an ecosystem. It is a key measure of an ecosystem's health and ability to support life. We distinguish between primary productivity (by producers) and secondary productivity (by consumers).

For Producers (Autotrophs): Net Primary Productivity (NPP) = Gross Primary Productivity (GPP) - Respiration (R) GPP is the total energy fixed by photosynthesis. R is the energy used by the producers for their own life processes. NPP is the energy available to herbivores.

For Consumers (Heterotrophs): Net Secondary Productivity (NSP) = Gross Secondary Productivity (GSP) - Respiration (R) GSP is the energy assimilated from food ( $GSP = \text{food eaten} - \text{faecal loss}$ ). R is the energy used by the consumer for its life processes. NSP is the formation of new biomass (growth and reproduction).

Nutrient Cycling: Carbon and Nitrogen

Unlike energy, which flows through an ecosystem and is lost, matter is cycled. Biogeochemical cycles describe the pathways of essential elements like carbon and nitrogen through the biotic (living) and abiotic (non-living) components of an ecosystem. We model these using storages (where the nutrient is held) and flows (the processes that move it).

Carbon Cycle: Key storages include the atmosphere ( $CO_2$ ), oceans, biomass, and fossil fuels. Key flows are photosynthesis (atmosphere to biomass), respiration (biomass to atmosphere), combustion (fossil fuels to atmosphere), and diffusion (atmosphere to ocean).
Nitrogen Cycle: The main storage is the atmosphere ( $N_2$ ). Key flows include nitrogen fixation (by bacteria or lightning, converting $N_2$ to ammonia), nitrification (ammonia to nitrates), assimilation (uptake by plants), denitrification (nitrates to $N_2$ ), and ammonification (decomposition).
Human Impact: Burning fossil fuels adds excess $CO_2$ to the atmosphere, enhancing the greenhouse effect. The industrial production of fertilisers (Haber-Bosch process) has doubled the rate of nitrogen fixation, leading to eutrophication in aquatic systems.

Worked examples

See the formulas applied — reveal one step at a time, like the exam.

EXAMPLE 1

In a temperate forest ecosystem, the Gross Primary Productivity (GPP) was measured to be 8,400 $kJ~m^{-2}~yr^{-1}$ . The plant community's respiratory losses (R) were found to be 4,600 $kJ~m^{-2}~yr^{-1}$ . Calculate the Net Primary Productivity (NPP) of this ecosystem.

1
1. State the formula: NPP = GPP - R [1 mark] 2. Substitute the values: NPP = 8,400 $kJ~m^{-2}~yr^{-1}$ - 4,600 $kJ~m^{-2}~yr^{-1}$ [1 mark for correct substitution] 3. Calculate the final answer with units: NPP = 3,800 $kJ~m^{-2}~yr^{-1}$ [1 mark for correct answer and units] Total: 3 marks

✓ FULLY WORKED

EXAMPLE 2

A population of rabbits in a meadow consumes 25,000 $kJ~m^{-2}~yr^{-1}$ of plant matter. They produce 16,000 $kJ~m^{-2}~yr^{-1}$ of faeces (egestion). Their respiratory heat loss is 7,500 $kJ~m^{-2}~yr^{-1}$ . a) Calculate the Gross Secondary Productivity (GSP). b) Calculate the Net Secondary Productivity (NSP).

1
a) Calculate GSP: 1. State the formula: GSP = Food eaten - Faecal loss [1 mark] 2. Substitute values: GSP = 25,000 - 16,000 $kJ~m^{-2}~yr^{-1}$ 3. Final Answer: GSP = 9,000 $kJ~m^{-2}~yr^{-1}$ [1 mark] b) Calculate NSP: 1. State the formula: NSP = GSP - R [1 mark] 2. Substitute values: NSP = 9,000 - 7,500 $kJ~m^{-2}~yr^{-1}$ 3. Final Answer: NSP = 1,500 $kJ~m^{-2}~yr^{-1}$ [1 mark] Total: 4 marks

✓ FULLY WORKED

How it all connects

The big idea sits in the middle — tap a linked idea to explore the link.

MAIN IDEAEnergy flow, productivity and nutrient cycles

Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.

Glossary

Try to recall each definition before you reveal it.

Quick check

Answer in your head first — then tap to check. No pressure.

Revision flashcards

Flip the card. Test yourself before the exam.

QUESTION · 1 / 12

Gross Primary Productivity (GPP)

TAP OR SPACE TO FLIP

ANSWER

The total amount of chemical energy produced by autotrophs in an ecosystem, typically through photosynthesis, per unit area per unit time. It's the total 'income' of energy before any is used. Units: $kJ~m^{-2}~yr^{-1}$ or $g~m^{-2}~yr^{-1}$ .

TAP OR SPACE TO FLIP BACK

1 / 12 · ← → space

Key takeaways

Review these before you close the topic — retrieval beats re-reading.

✓
First Law of Thermodynamics: Energy can be transferred and transformed, but it cannot be created or destroyed. In ecosystems, this means solar energy is converted to chemical energy, which is then transferred between trophic levels.
✓
Second Law of Thermodynamics: During any energy conversion, some energy is lost as heat, and the entropy (disorder) of the universe increases. This explains why energy transfers are inefficient (the '10% rule') and why food chains are limited in length. Energy is lost as heat during respiration at each trophic level.

Practice — then mark it

The whole point: a real Cambridge question, marked mark-by-mark.

Real past paper[0]

Test Your Knowledge on Energy Flow and Nutrient Cycles

Do it on paper → mark itMARKED MARK-BY-MARK · B1 / M1 / A1 · OFFICIAL SCHEME

Extra simulations & links

PhET, GeoGebra and other curated tools — open in a new tab.

Frequently asked

✓

Checkpoint

One marked question is worth ten re-reads — close the loop before you move on.

Checkpoint

Reading it isn’t knowing it — prove it.

Before you move on: do Test Your Knowledge on Energy Flow and Nutrient Cycles on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.

Attempt & get marked →Takes about a minute · you’ll land back on this lesson

← PREVIOUS2.1 Ecosystems and ecology NEXT →3.1 Biodiversity and conservation

Energy flow, productivity and nutrient cycles

BY THE END, YOU CAN…

1Explain the pathways of energy flow through ecosystems, including inputs, transfers, and outputs.
2Calculate and interpret values for gross and net productivity in producers and consumers.
3Describe the carbon and nitrogen cycles, identifying key storages, flows, and human impacts.
4Distinguish between the flow of energy and the cycling of matter in an ecosystem.

In simple terms

A friendly intro before the formal notes — no formulas yet.

The Ecosystem's Economy

THINK OF IT LIKE…

1
First, identify the source of energy (usually the sun) and trace its path through different trophic levels, remembering that energy is lost at each step.
2
Next, distinguish between Gross Productivity (total energy assimilated) and Net Productivity (energy left for growth after respiration). Use the formulas NPP = GPP - R and NSP = GSP - R.
3
Then, analyse nutrient cycles like carbon and nitrogen by identifying the main storages (sinks) and the processes that move nutrients between them (flows or fluxes).
4
Finally, evaluate human impacts on these cycles, such as burning fossil fuels (carbon cycle) or using fertilisers (nitrogen cycle), and their consequences.

Explore the concept

Use the live diagram and synced steps — play it or tap a step card to walk through.

Key formulas

Tap any symbol to reveal exactly what it means and its units.

Net Primary Productivity (NPP) = Gross Primary Productivity (GPP) - Respiration (R)

Net Secondary Productivity (NSP) = Gross Secondary Productivity (GSP) - Respiration (R)

Full topic notes

Formal explanation with the rigour you need for the exam.

Energy Flow and the Laws of Thermodynamics

First Law of Thermodynamics: Energy can be transferred and transformed, but it cannot be created or destroyed. In ecosystems, this means solar energy is converted to chemical energy, which is then transferred between trophic levels.
Second Law of Thermodynamics: During any energy conversion, some energy is lost as heat, and the entropy (disorder) of the universe increases. This explains why energy transfers are inefficient (the '10% rule') and why food chains are limited in length. Energy is lost as heat during respiration at each trophic level.

Ecosystem Productivity

Nutrient Cycling: Carbon and Nitrogen

Carbon Cycle: Key storages include the atmosphere ( $CO_2$ ), oceans, biomass, and fossil fuels. Key flows are photosynthesis (atmosphere to biomass), respiration (biomass to atmosphere), combustion (fossil fuels to atmosphere), and diffusion (atmosphere to ocean).
Nitrogen Cycle: The main storage is the atmosphere ( $N_2$ ). Key flows include nitrogen fixation (by bacteria or lightning, converting $N_2$ to ammonia), nitrification (ammonia to nitrates), assimilation (uptake by plants), denitrification (nitrates to $N_2$ ), and ammonification (decomposition).
Human Impact: Burning fossil fuels adds excess $CO_2$ to the atmosphere, enhancing the greenhouse effect. The industrial production of fertilisers (Haber-Bosch process) has doubled the rate of nitrogen fixation, leading to eutrophication in aquatic systems.

Worked examples

See the formulas applied — reveal one step at a time, like the exam.

EXAMPLE 1

1
1. State the formula: NPP = GPP - R [1 mark] 2. Substitute the values: NPP = 8,400 $kJ~m^{-2}~yr^{-1}$ - 4,600 $kJ~m^{-2}~yr^{-1}$ [1 mark for correct substitution] 3. Calculate the final answer with units: NPP = 3,800 $kJ~m^{-2}~yr^{-1}$ [1 mark for correct answer and units] Total: 3 marks

✓ FULLY WORKED

EXAMPLE 2

1
a) Calculate GSP: 1. State the formula: GSP = Food eaten - Faecal loss [1 mark] 2. Substitute values: GSP = 25,000 - 16,000 $kJ~m^{-2}~yr^{-1}$ 3. Final Answer: GSP = 9,000 $kJ~m^{-2}~yr^{-1}$ [1 mark] b) Calculate NSP: 1. State the formula: NSP = GSP - R [1 mark] 2. Substitute values: NSP = 9,000 - 7,500 $kJ~m^{-2}~yr^{-1}$ 3. Final Answer: NSP = 1,500 $kJ~m^{-2}~yr^{-1}$ [1 mark] Total: 4 marks

✓ FULLY WORKED

How it all connects

The big idea sits in the middle — tap a linked idea to explore the link.

MAIN IDEAEnergy flow, productivity and nutrient cycles

Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.

Glossary

Try to recall each definition before you reveal it.

Quick check

Answer in your head first — then tap to check. No pressure.

Revision flashcards

Flip the card. Test yourself before the exam.

QUESTION · 1 / 12

Gross Primary Productivity (GPP)

TAP OR SPACE TO FLIP

ANSWER

TAP OR SPACE TO FLIP BACK

1 / 12 · ← → space

Key takeaways

Review these before you close the topic — retrieval beats re-reading.

✓
First Law of Thermodynamics: Energy can be transferred and transformed, but it cannot be created or destroyed. In ecosystems, this means solar energy is converted to chemical energy, which is then transferred between trophic levels.
✓
Second Law of Thermodynamics: During any energy conversion, some energy is lost as heat, and the entropy (disorder) of the universe increases. This explains why energy transfers are inefficient (the '10% rule') and why food chains are limited in length. Energy is lost as heat during respiration at each trophic level.

Practice — then mark it

The whole point: a real Cambridge question, marked mark-by-mark.

Real past paper[0]

Test Your Knowledge on Energy Flow and Nutrient Cycles

Do it on paper → mark itMARKED MARK-BY-MARK · B1 / M1 / A1 · OFFICIAL SCHEME

Extra simulations & links

PhET, GeoGebra and other curated tools — open in a new tab.

Frequently asked

✓

Checkpoint

One marked question is worth ten re-reads — close the loop before you move on.

Checkpoint

Reading it isn’t knowing it — prove it.

Before you move on: do Test Your Knowledge on Energy Flow and Nutrient Cycles on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.

Attempt & get marked →Takes about a minute · you’ll land back on this lesson

← PREVIOUS2.1 Ecosystems and ecology NEXT →3.1 Biodiversity and conservation

Revise Energy flow, productivity and nutrient cycles for IB Environmental Systems and Societies (2.2)

In simple terms

Explore the concept

Key formulas

Full topic notes

Energy Flow and the Laws of Thermodynamics

Ecosystem Productivity

Nutrient Cycling: Carbon and Nitrogen

Worked examples

How it all connects

Glossary

Quick check

Revision flashcards

Key takeaways

Practice — then mark it

Test Your Knowledge on Energy Flow and Nutrient Cycles

Extra simulations & links

Frequently asked

Checkpoint

Reading it isn’t knowing it — prove it.

In simple terms

Explore the concept

Key formulas

Full topic notes

Energy Flow and the Laws of Thermodynamics

Ecosystem Productivity

Nutrient Cycling: Carbon and Nitrogen

Worked examples

How it all connects

Glossary

Quick check

Revision flashcards

Key takeaways

Practice — then mark it

Test Your Knowledge on Energy Flow and Nutrient Cycles

Extra simulations & links

Frequently asked

Checkpoint

Reading it isn’t knowing it — prove it.

Discuss Energy flow, productivity and nutrient cycles