Energy transferred in ecosystemsOxford AQA IGCSE Biology: Flashcards

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What is a food chain?

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What is a food chain?: A food chain is a sequence of organisms showing the transfer of energy and nutrients from one organism to the next, beginning with a producer and progressing through consumers.
Define a food web.: A food web is a network of interconnected food chains in an ecosystem, showing multiple feeding relationships and energy pathways between different organisms.
Name four ways energy is lost at each trophic level.: Energy is lost through: respiration (heat released), egestion (faeces expelled), excretion (urine and other waste products), and incomplete ingestion of prey organisms.
Why does the length of food chains rarely exceed four or five trophic levels?: Energy is lost at each trophic level through respiration, egestion, excretion and heat. Only approximately 10% of energy is transferred to the next trophic level, so insufficient energy remains to support additional levels.
What is the approximate energy transfer efficiency between consecutive trophic levels?: Approximately 10% of energy is transferred from one trophic level to the next; alternatively, about 90% of energy is lost at each trophic level.
Calculate the energy available to secondary consumers if primary consumers receive 2000 kJ of energy.: Secondary consumers would receive approximately 200 kJ of energy (10% of 2000 kJ), calculated as: energy transfer = energy available × 0.1 or ÷ 10.
Describe the role of photosynthesis in the carbon cycle.: Photosynthesis removes carbon dioxide from the atmosphere and converts it into organic compounds (glucose) in plant tissues, incorporating carbon into the ecosystem.
Name the four main processes of the carbon cycle.: The four main processes are: photosynthesis (uptake of CO₂), respiration (release of CO₂), decomposition (release of CO₂ by decomposers), and combustion (burning of fossil fuels releases CO₂).
What is fossilisation in the carbon cycle?: Fossilisation is the slow conversion of dead organisms into fossil fuels (coal, oil, natural gas) over millions of years, locking carbon away from the atmosphere for extended periods.
Describe nitrogen fixation.: Nitrogen fixation is the process by which certain bacteria (including Rhizobium in root nodules and free-living soil bacteria) convert atmospheric nitrogen (N₂) into ammonia (NH₃) for use by plants.
Define nitrification in the nitrogen cycle.: Nitrification is the oxidation of ammonia (NH₃) into nitrates (NO₃⁻) by nitrifying bacteria in the soil, making nitrogen available for plant absorption.
Explain denitrification in the nitrogen cycle.: Denitrification is the process by which denitrifying bacteria convert nitrates (NO₃⁻) back into atmospheric nitrogen (N₂), removing nitrogen from the soil and returning it to the atmosphere.
Describe the role of decomposers in the nitrogen cycle.: Decomposers break down dead organisms and waste products, converting organic nitrogen into ammonia (NH₃) through decomposition, which can then be nitrified or utilised by other organisms.
Name the four main processes of the water cycle.: The four main processes are: evaporation (water from surface to vapour), condensation (vapour to liquid), precipitation (water falls as rain/snow), and transpiration (water from plants to atmosphere).
What is the difference between evaporation and transpiration in the water cycle?: Evaporation is the loss of water from soil, water bodies and organisms to the atmosphere, whilst transpiration is specifically the loss of water vapour from plant leaves through stomata.