Lesson 3.5.3.1

3.5.3.1 Biomass and net primary productivity Quiz: AQA Biology, Unit 5

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.5.3.1, Biomass and net primary productivity: 20 multiple choice questions for the AQA Biology (7402), Unit 5: Energy transfers in and between organisms, written with Revision Ninja.

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The 20 questions

  1. What is gross primary production (GPP)?

    • The chemical energy store in plant biomass after respiratory losses
    • The energy released by respiration in a plant cell
    • The energy transferred from plants to herbivores
    • The chemical energy store in plant biomass in a given area or volume

  2. Which equation correctly defines net primary production (NPP)?

    • NPP = R - GPP
    • NPP = GPP + R
    • NPP = GPP - R
    • NPP = GPP / R

  3. Biomass can be measured in terms of which of the following?

    • Mass of carbon or dry mass of tissue per given area
    • Number of individual plants per hectare only
    • Volume of water absorbed by the roots only
    • Colour of the leaves

  4. What does calorimetry estimate in dry biomass?

    • The rate of transpiration
    • The water content of fresh tissue
    • The number of species present
    • The chemical energy store in the dry biomass

  5. Which unit is an example of a unit for primary productivity?

    • mol dm^-3 per cell
    • kg m^-1 s^-1 per species
    • % yield per gram
    • kJ ha^-1 year^-1

  6. What are most of the sugars made by plants used for?

    • Conversion directly into carbon dioxide
    • Storage as dissolved oxygen
    • Excretion as waste
    • Respiratory substrates

  7. Net primary production is described as available for which of the following?

    • Only the growth of the root system
    • Only photosynthesis in the next season
    • Only the production of oxygen
    • Plant growth and reproduction, and other trophic levels such as herbivores and decomposers

  8. A plant has GPP of 5000 kJ and respiratory losses of 1800 kJ. What is its NPP?

    • 1800 kJ
    • 3200 kJ
    • 2778 kJ
    • 6800 kJ

  9. An ecosystem has GPP of 8400 kJ per square metre per year and NPP of 5100 kJ per square metre per year. What are the respiratory losses?

    • 5100 kJ per square metre per year
    • 13 500 kJ per square metre per year
    • 3300 kJ per square metre per year
    • 1700 kJ per square metre per year

  10. A field has GPP of 2500 kJ per square metre per year, with respiratory losses equal to 40% of GPP. What is the NPP?

    • 1000 kJ per square metre per year
    • 1500 kJ per square metre per year
    • 2100 kJ per square metre per year
    • 2500 kJ per square metre per year

  11. A 0.5 g sample of dry plant biomass releases 10 kJ when burnt in a calorimeter. How much energy is stored per kilogram of dry biomass?

    • 200 kJ
    • 20 000 kJ
    • 20 kJ
    • 5 kJ

  12. Why is dry mass used rather than fresh mass when measuring biomass?

    • Dry mass includes the water that plants absorb
    • Water content varies, so dry mass gives a consistent measure of organic material
    • Fresh mass cannot be weighed on a balance
    • Dry mass is the only measure that includes carbon

  13. Which process accounts for the difference between GPP and NPP?

    • Transpiration
    • Respiration
    • Egestion
    • Photosynthesis

  14. A forest has GPP of 20 000 and respiratory losses of 12 000 kJ, while a grassland has GPP of 8000 and respiratory losses of 3000 kJ. Which has the higher NPP?

    • The grassland, with NPP of 5000 compared with 8000
    • The forest, with NPP of 8000 compared with 5000
    • Both have the same NPP
    • The grassland, because its GPP is lower

  15. A crop has GPP of 25 000 kJ per hectare per year, with respiratory losses of 60% of GPP. What is its NPP?

    • 25 000 kJ per hectare per year
    • 15 000 kJ per hectare per year
    • 40 000 kJ per hectare per year
    • 10 000 kJ per hectare per year

  16. Two plots have the same GPP, but plot P has higher respiratory losses. What is the most likely consequence for plot P?

    • It has more biomass because respiration removes waste
    • It has higher NPP because respiration adds energy
    • It has lower NPP and so less energy is available for plant growth and reproduction
    • It has the same NPP because GPP is equal

  17. Which factor would most reduce NPP without changing GPP?

    • A decrease in light intensity that does not affect respiration
    • A rise in the number of species present
    • A reduction in the number of decomposers
    • An increase in respiratory losses, for example at high temperatures

  18. The GPP of a grassland is 9000 kJ per square metre per year and NPP is 3600 kJ per square metre per year. What fraction of GPP is lost to respiration?

    • 40%
    • 25%
    • 75%
    • 60%

  19. Explain why plants do not use all their GPP for growth. Which statement is most accurate?

    • Plants store all of GPP as starch without any losses
    • Plants release GPP as oxygen to the atmosphere
    • Plants use GPP only to make new roots
    • Plants use part of GPP in respiration to release energy for their own metabolism

  20. A plant has GPP of 4000 kJ per square metre per year and NPP of 2500 kJ per square metre per year. What percentage of GPP is lost to respiration?

    • 15%
    • 62.5%
    • 25%
    • 37.5%

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