5.2.1Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Ecological Productivity — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 6 parts Lesson 16 of 36 Unit quiz
Curriculum Equation Key معادلة التنفس الخلوي الهوائي الموزونة - Balanced Cellular Respiration EquationFast Exam Solution
C₆H₁₂O₆ + 6O₂ ➔ 6CO₂ + 6H₂O + 36-38 ATP
Word Equation & Conditions: Glucose + Oxygen -> Carbon Dioxide + Water + Energy (36-38 ATP) | جلوكوز + أكسجين ← ثاني أكسيد كربون + ماء + طاقة
Location & Specifications: الميتوكوندريا (Mitochondria) والسيتوسول.
Part 1 of 6Primary Productivity
Primary productivity is the rate at which producers store energy in organic molecules.
GPP
- GPP Gross primary productivity is the rate at which chemical energy is made by photosynthesis in a given area.
Respiratory loss
- Respiratory loss Plants respire, so a large proportion of the energy fixed is released as heat and used for ATP.
NPP
- NPP Net primary productivity is the energy stored in plant biomass after respiratory losses, NPP = GPP - R.
Importance
- Importance NPP is the energy available to herbivores, decomposers and every higher trophic level.
Units
- Units Productivity is a rate per area, such as kJ m⁻² year⁻¹ or g m⁻² year⁻¹.
Part 2 of 6Productivity of Consumers
Consumers gain energy by ingestion, not photosynthesis.
Productivity of Consumers
Ingested energy
- Ingested energy Only part of the energy in the food eaten is absorbed, because some is lost as undigested material.
Faeces and urine
- Faeces and urine Energy in faeces and nitrogenous waste is not available for growth.
Respiration
- Respiration Respiration releases much of the absorbed energy as heat and for movement.
Equation
- Equation Net production of consumers N = I - (F + R), where I is intake and F is faeces and urine.
Part 3 of 6Factors Affecting Productivity
Productivity differs between ecosystems and seasons.
1
Light intensity, which varies with season, latitude and cloud cover, limits the rate of photosynthesis.
2
Temperature affects enzyme activity so productivity is low in cold regions.
3
Water and mineral availability, especially nitrate and phosphate, affect growth.
4
Agriculture increases NPP by adding fertiliser, irrigating and removing competing plants.
| Ecosystem | Typical NPP |
|---|---|
| Tropical rainforest | Very high |
| Open ocean | Low per area |
| Desert | Very low |
Part 4 of 6Why Energy Is Not All Useful
Light lost
- Light lost Much of the incident light is reflected, transmitted or is of the wrong wavelength.
Heat
- Heat Energy released in respiration becomes heat and cannot be recycled.
Efficiency
- Efficiency Only a small fraction of incident light energy becomes chemical energy in NPP.
Link
- Link NPP controls how much biomass supports the food web.
Part 5 of 6Worked Example
Question
- A grassland has GPP of 18 000 kJ m⁻² year⁻¹ and plant respiration of 7 200 kJ m⁻² year⁻¹.
- Calculate NPP and the percentage of GPP that becomes NPP.
- NPP = GPP - R = 18 000 - 7 200 = 10 800 kJ m⁻² year⁻¹.
- Percentage = 10 800 / 18 000 x 100 = 60 percent.
Answer NPP = 10 800 kJ m⁻² year⁻¹, which is 60 percent of GPP.
Part 6 of 6Exam Checklist & Tips
5.2.1 – Key Points for the Exam
- GPP Gross primary productivity, the total rate of energy fixation by photosynthesis.
- NPP Net primary productivity, GPP minus respiratory loss R.
- Productivity The rate at which energy or biomass is made per unit area.
- Biomass The mass of organic material in organisms, usually measured as dry mass.
Common Mistakes
- Writing NPP = GPP + R; respiration is subtracted.
- Giving productivity without units that include time.
- Confusing biomass, a mass, with productivity, a rate.
- Forgetting that net production of consumers also loses energy in faeces.
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