Cycles within Ecosystems (Edexcel GCSE Combined Science: Biology): Flashcards
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- FrontThe Water Cycle
Evaporation
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Evaporation
When energy from the Sun heats water in oceans, rivers and lakes, turning it into water vapour that enters the atmosphere.
Precipitation
Water returning to Earth as rain, snow or sleet when the water droplets in clouds become big and heavy.
What are the two ways water enters the atmosphere as water vapour?
Evaporation from oceans, rivers and lakes (using energy from the Sun), and transpiration from plants.
How do clouds form in the water cycle?
Warm air rises and cools, so the water vapour condenses back into liquid water, forming clouds.
Why is the water cycle important for life?
It distributes fresh water globally, providing clean water for drinking and supporting processes such as photosynthesis.
What is potable water?
Water that is safe to drink.
What is desalination?
Removing the excess mineral ions (salts) from salty water, such as sea water, to make it drinkable.
Describe distillation as a method of desalination.
Saline water is boiled, the water vapour is funnelled through a tube, then it is condensed and the pure water is collected.
How does reverse osmosis produce potable water?
Saline water is forced at high pressure through a partially permeable membrane, which filters out the mineral ions, leaving pure water.
Water vapour is released from plants into the air by .
transpiration
As warm air rises and cools, water vapour back into liquid water, forming clouds.
condenses
Combustion
The burning of fossil fuels, which combines carbon with oxygen and releases carbon dioxide into the atmosphere.
How is carbon dioxide removed from the atmosphere?
By plants (producers), which take it in to use for photosynthesis.
How is carbon passed from plants to animals?
By feeding.
Which process returns carbon dioxide to the atmosphere from plants, animals and microorganisms?
Respiration.
How are fossil fuels formed?
When animals and plants die where decomposing microorganisms are absent, the carbon in their bodies is converted, over millions of years and under pressure, into fossil fuels.
Give two human activities that increase the carbon dioxide content of the atmosphere.
Increased burning (combustion) of fossil fuels, and mass deforestation.
How does deforestation increase atmospheric carbon dioxide?
It reduces the number of producers available to remove CO₂ by photosynthesis, and burning the cleared trees releases yet more CO₂.
Why is the carbon cycle important?
Carbon is a component of all organic molecules essential for life (e.g. glucose); the cycle recycles carbon so new organisms can be made and grow.
Name two global reservoirs between which carbon moves.
Any two of: the atmosphere, biomass, the ocean and the soil.
Carbon is removed from the atmosphere by plants during and returned to it by .
photosynthesis / respiration
When fossil fuels are burned during , carbon dioxide is released into the atmosphere.
combustion
Nitrogen fixation
When nitrogen-fixing bacteria convert nitrogen gas (N₂) into ammonium compounds, which can then be converted into usable nitrates.
Denitrification
When denitrifying bacteria convert nitrates in the soil into nitrogen gas, which returns to the atmosphere.
Why do plants and animals need nitrogen?
To produce proteins and nucleic acids (DNA and RNA).
Why can't plants use nitrogen gas from the air directly?
They cannot access nitrogen in its gaseous form, so they rely on bacteria to convert it into nitrogen-containing compounds (nitrates) that they can take up.
What happens during ammonification?
Saprobionts (decomposers such as fungi and bacteria) convert nitrogen compounds in waste and dead organisms into ammonia, which forms ammonium ions in the soil.
What happens during nitrification?
Nitrifying bacteria convert ammonium ions into nitrites, and then different nitrifying bacteria convert the nitrites into nitrates.
Under what conditions does denitrification occur?
In anaerobic conditions (little or no oxygen), such as in waterlogged soil.
Besides bacteria, what else can fix nitrogen from the air?
Lightning, which splits the bond between the two nitrogen atoms, forming nitrous oxides that dissolve in rainwater and leach into the soil.
Where can nitrogen-fixing bacteria be found?
Free-living in the soil, or living within the root nodules of some plants.
Nitrogen-fixing bacteria convert nitrogen gas into ammonium compounds in a process called nitrogen .
fixation
Decomposers called convert nitrogen compounds in dead organisms and waste into ammonia.
saprobionts
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