3.9.7Additional lessons
Primary and Secondary Production — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 25 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.
Section 1 of 5Primary Production
Primary production is the rate at which producers convert inorganic carbon into organic matter.
Gross primary production
- Gross primary production GPP is the total quantity of organic matter made by producers in photosynthesis in a given area and time.
Respiration
- Respiration Producers use part of their GPP in their own respiration, which is lost as carbon dioxide and heat.
Net primary production
- Net primary production NPP is the organic matter that remains and builds biomass, found by subtracting respiration from GPP.
Equation
- Equation NPP = GPP − R, where R is the energy or biomass used in respiration.
Units
- Units Production is measured per unit area per unit time, for example g m⁻² yr⁻¹ or kJ m⁻² yr⁻¹.
Section 2 of 5Secondary Production
Secondary Production
Definition
- Definition Secondary production is the formation of new biomass by consumers, which are heterotrophs, through feeding on other organisms.
Gross secondary production
- Gross secondary production This is the total energy or matter that consumers assimilate from their food.
Net secondary production
- Net secondary production This is the assimilated amount minus the part used in respiration, and it is what builds new consumer biomass.
Available to the next level
- Available to the next level Net production is the biomass that predators or decomposers can obtain.
Section 3 of 5Measuring Production
1
Mark out an area and harvest the organisms at the start, then dry them in an oven until the mass is constant.
2
Harvest a similar sample at the end of the period and dry it in the same way.
3
The increase in dry mass per unit area gives the net production for the period.
4
Compare ecosystems: tropical rainforests have a high NPP per unit area, whereas deserts and tundra have a low NPP.
| Measure | Equation |
|---|---|
| Net primary production | GPP − R |
| Net secondary production | Assimilation − R |
| Percentage NPP of GPP | NPP ÷ GPP × 100 |
Section 4 of 5Worked Example
Question
- A grassland has a gross primary production of 12 000 kJ m⁻² yr⁻¹, and the plants use 7 800 kJ m⁻² yr⁻¹ in respiration.
- Calculate the net primary production and the percentage of GPP that it represents.
- NPP = GPP − R = 12 000 − 7 800 = 4 200 kJ m⁻² yr⁻¹.
- Percentage = NPP ÷ GPP × 100 = 4 200 ÷ 12 000 × 100 = 35%.
Answer The NPP is 4 200 kJ m⁻² yr⁻¹, which is 35% of the GPP.
Section 5 of 5Exam Checklist & Tips
3.9.7 – Key Points for the Exam
- GPP The total organic matter made by photosynthesis in a given area and time.
- NPP GPP minus the part used in the producers' respiration.
- Secondary production Biomass produced by consumers.
- Productivity Rate of production of biomass per unit area per time.
- Dry mass Mass after all water is removed, used to measure biomass.
Common Mistakes
- Writing that NPP is greater than GPP, which can never be so.
- Measuring production with fresh mass, which includes variable water content.
- Forgetting the time period in the units of production.
- Using the term primary production for consumers.
Last updated:
\n