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MYP Biology Topic Ecosystem Cycles Revision Notes | RevisionDojo

Why Do Ecosystems Need Nutrient Cycles?

All living organisms need elements like carbon, nitrogen, and phosphorus to build their bodies.
Unlike energy, which flows and is eventually lost as heat, matter is recycled.
Earth receives constant sunlight, but almost no new matter. Nutrients must therefore move in continuous loops.

Definition

Nutrient cycle

The continuous movement of essential chemical elements through living organisms and the environment.

Note

The key idea here is that energy flows, while matter cycles.
Without nutrient cycling, ecosystems would run out of usable materials.

Why Don’t Nutrients Run Out?

Nutrients are reused through a repeating loop:
1. Producers absorb minerals from soil, water, or air.
2. Consumers obtain nutrients by feeding.
3. Decomposers break down dead organisms and waste, returning nutrients to the environment.
4. Nutrients re-enter producers, completing the cycle.

Analogy

Energy = spending money (once gone, it’s gone).
Nutrients = recycling bins (materials are cleaned and reused).

What Happens When a Nutrient Cycle Is Disrupted?

If a cycle breaks or becomes unbalanced, entire ecosystems shift.
The effects of this disruption include:
1. Nutrient depletion → reduced plant growth, lower productivity.
2. Nutrient overload → pollution, algal blooms, oxygen loss in water.
3. Species loss → organisms cannot obtain essential nutrients.
4. Community changes → fast-growing or opportunistic species dominate.

Example

Excess phosphorus from fertilizers enters rivers, leading to rapid algal growth.
This causes water to become turbid and light to become blocked.
Algal decay depletes dissolved oxygen, creating hypoxic “dead zones.”
Results include fish kills and biodiversity loss; reduce runoff with buffer strips and smarter fertilizer timing/doses.

How Does Carbon Moves Through Living Systems? (Carbon Cycle)

Carbon is the backbone of organic molecules, moving between the atmosphere and living things through predictable processes.

Photosynthesis
1. Plants and algae take CO₂ from the atmosphere and convert it into glucose.
2. Carbon moves into living organisms.
Respiration
1. All organisms respire, releasing CO₂ back to the atmosphere.
Feeding & Decomposition

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Definition

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MYP Biology Ecosystem Cycles Notes

Why Do Ecosystems Need Nutrient Cycles?

Why Don’t Nutrients Run Out?

What Happens When a Nutrient Cycle Is Disrupted?

How Does Carbon Moves Through Living Systems? (Carbon Cycle)

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Why Do Ecosystems Need Nutrient Cycles?

Why Don’t Nutrients Run Out?

What Happens When a Nutrient Cycle Is Disrupted?

How Does Carbon Moves Through Living Systems? (Carbon Cycle)

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Cells7 subtopics

Organisms7 subtopics

Processes10 subtopics

Metabolism4 subtopics

Evolution7 subtopics

Interactions with environment6 subtopics

Interactions between organisms5 subtopics

Human interactions with environments3 subtopics

Biotechnology3 subtopics

MYP Biology Ecosystem Cycles Notes

Cells7 subtopics

Organisms7 subtopics

Processes10 subtopics

Metabolism4 subtopics

Evolution7 subtopics

Interactions with environment6 subtopics

Interactions between organisms5 subtopics

Human interactions with environments3 subtopics

Biotechnology3 subtopics

Why Do Ecosystems Need Nutrient Cycles?

Why Don’t Nutrients Run Out?

What Happens When a Nutrient Cycle Is Disrupted?

How Does Carbon Moves Through Living Systems? (Carbon Cycle)

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Why Do Ecosystems Need Nutrient Cycles?

Why Don’t Nutrients Run Out?

What Happens When a Nutrient Cycle Is Disrupted?

How Does Carbon Moves Through Living Systems? (Carbon Cycle)

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account