Lesson 6.3.1a

6.3.1a Ecosystems, energy flow and nutrient recycling Quiz: OCR Biology, Unit 9

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6.3.1a, Ecosystems, energy flow and nutrient recycling: 20 multiple choice questions for the OCR Biology (H020), Unit 9: Ecosystems, written with Revision Ninja.

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The 20 questions

  1. How is the efficiency of biomass transfer between trophic levels calculated?

    • (Intake ÷ transferred) × 100
    • (Transferred ÷ loss) × 100
    • (Respiration ÷ intake) × 100
    • (Transferred ÷ intake) × 100

  2. What is the role of Nitrosomonas bacteria in the nitrogen cycle?

    • Nitrate to nitrogen
    • Ammonium to nitrite
    • Nitrite to nitrate
    • Nitrogen to ammonia

  3. What reaction is catalysed by Nitrobacter bacteria in the nitrogen cycle?

    • Nitrogen to ammonia
    • Nitrate to nitrogen
    • Ammonium to nitrite
    • Nitrite to nitrate

  4. What is the primary function of Rhizobium bacteria in legumes?

    • Denitrification
    • Nitrification
    • Ammonification
    • Nitrogen fixation

  5. Which organisms typically act as pioneer species on bare rock during primary succession?

    • Hardwood trees
    • Mosses
    • Lichens
    • Shrubs

  6. What term describes the final, stable community achieved at the end of ecological succession?

    • Deflected climax
    • Pioneer community
    • Seral stage
    • Climax community

  7. What term describes an organism's feeding position in a food chain?

    • Ecosystem stage
    • Trophic cascade
    • Niche
    • Trophic level

  8. A herbivore takes in 500 kJ of food and stores 50 kJ as biomass. What is the efficiency of biomass transfer?

    • 1%
    • 90%
    • 10%
    • 50%

  9. If producers store 10,000 kJ and each transfer is 10% efficient, how much energy reaches tertiary consumers?

    • 1 kJ
    • 10 kJ
    • 100 kJ
    • 1000 kJ

  10. Why does energy flow through an ecosystem rather than being recycled like nutrients?

    • Lost as heat
    • Destroyed in respiration
    • Reflected by leaves
    • Stored in soil

  11. Which agricultural practice naturally increases soil nitrate levels using nitrogen-fixing bacteria?

    • Flooding fields
    • Spreading animal manure
    • Planting leguminous crops
    • Adding lime powder

  12. What process converts soil nitrates back into atmospheric nitrogen gas?

    • Denitrification
    • Nitrification
    • Ammonification
    • Nitrogen fixation

  13. Which organisms break down dead matter and return carbon dioxide to the atmosphere via respiration?

    • Nitrifying bacteria
    • Autotrophs
    • Decomposers
    • Primary consumers

  14. A tertiary consumer has an intake of 300 g from a population of secondary consumers that contains 15 g of biomass. What is the efficiency of biomass transfer?

    • 20%
    • 0.5%
    • 5%
    • 15%

  15. Which of the following is an abiotic factor in an ecosystem?

    • Predators
    • Soil pH
    • Competitors
    • Bacteria

  16. What is the typical efficiency of biomass transfer between trophic levels in an ecosystem?

    • 50%
    • 10%
    • 1%
    • 90%

  17. Producers store 20,000 kJ and each transfer between trophic levels is 10% efficient. How much energy reaches tertiary consumers?

    • 2000 kJ
    • 10 kJ
    • 20 kJ
    • 200 kJ

  18. Why does removing crop biomass cause nitrogen levels in soil to fall over time?

    • Increased denitrification rates
    • Reduced nitrogen fixation
    • Excessive nitrate leaching
    • Nitrogen biomass removed

  19. Primary consumers take in 400 kg of biomass and the transfer efficiency is 15%. How much biomass is transferred?

    • 400 kg
    • 60 kg
    • 15 kg
    • 6 kg

  20. Which term describes the total mass of living material in a specific area at a given time?

    • Biomass
    • Net production
    • Gross productivity
    • Standing crop

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