3.9.1Additional lessons
Ecosystems as Open Systems — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 19 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Open, Closed and Isolated Systems
Ecologists describe an ecosystem by what crosses its boundary.
System
- System A system is a set of components that interact and are considered together, such as a pond, a forest or the whole of the biosphere.
Open system
- Open system An open system exchanges both energy and matter with its surroundings, which is true of most ecosystems.
Closed system
- Closed system A closed system exchanges energy but not matter with its surroundings, and Earth as a whole is close to this.
Isolated system
- Isolated system An isolated system exchanges neither energy nor matter, and no real ecosystem is truly isolated.
Part 2 of 5Inputs and Outputs of an Ecosystem
Inputs and Outputs of an Ecosystem
Energy input
- Energy input Light energy from the Sun enters and is converted into chemical energy by photosynthesis in producers.
Energy output
- Energy output Energy leaves as heat, produced mainly by respiration, and is radiated back to the atmosphere and space.
Matter input
- Matter input Water, gases and minerals enter through rainfall, wind, rivers and the movement of animals.
Matter output
- Matter output Matter leaves in run-off, harvested crops, migration, gases from respiration and drainage of dissolved ions.
Part 3 of 5Sustainability of Ecosystems
1
Producers absorb nutrients, such as nitrate and phosphate ions, from the soil or water and build them into organic compounds.
2
Consumers obtain these nutrients by feeding, and waste and dead matter pass the nutrients on to decomposers.
3
Decomposers return the nutrients to the soil or water in inorganic form, ready for uptake by producers again.
4
Because nutrients are recycled while energy flows through in one direction, an ecosystem can persist for a very long time, provided the Sun keeps supplying energy.
| Item | Behaviour in an ecosystem |
|---|---|
| Energy | Flows in one direction, entering as light and leaving as heat |
| Nutrients | Recycled between organisms and the physical environment |
| Water | Cycles via evaporation, rainfall and run-off |
Part 4 of 5Worked Illustration: A Pond
Energy in
- Energy in Sunlight falls on the pond and is captured by algae and water plants, which supply organic compounds to the rest of the community.
Matter in
- Matter in Streams and rainfall bring water and dissolved ions, while oxygen and carbon dioxide are exchanged with the air.
Matter out
- Matter out Water drains out of the pond, insects with aquatic larvae fly away as adults, and fish may be caught by birds from outside.
Energy out
- Energy out All the organisms release heat through respiration, which warms the water and is lost to the air.
Recycling
- Recycling Bacteria and fungi decompose dead plants and animals on the bottom, returning nitrate and phosphate ions to the water.
Part 5 of 5Exam Checklist & Tips
3.9.1 – Key Points for the Exam
- Open system A system that exchanges energy and matter with its surroundings.
- Closed system A system that exchanges energy but not matter.
- Decomposer An organism that breaks down dead matter and releases nutrients.
- Sustainability The ability of an ecosystem to continue without outside intervention.
- Biosphere All the parts of Earth where life exists.
Common Mistakes
- Saying ecosystems are closed systems because nutrients are recycled;
- they still exchange matter with surroundings.
- Thinking energy is recycled, when it flows and is lost as heat.
- Forgetting that energy leaving the ecosystem is mostly heat.
- Confusing an isolated system with a closed one.
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