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What is the water cycle?
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What is the water cycle?
The water cycle is the series of processes by which water moves through an ecosystem.
How does water enter the atmosphere during the water cycle?
Water enters the atmosphere during the water cycle by:
evaporation, e.g. from seas and lakes
transpiration from the leaves of plants
During the water cycle, in the atmosphere condenses to form .
During the water cycle, water vapour in the atmosphere condenses to form clouds.
True or False?
Water vapour returns to the earth as precipitation during the water cycle.
True.
Water from the atmosphere returns to the earth as precipitation, e.g. rain or snow.
How can water from the environment be made potable?
Water can be made potable, or drinkable, as follows:
desalination, e.g. by distillation or reverse osmosis
treatment to remove pathogens and toxins
How is carbon taken out of the atmosphere during the carbon cycle?
Carbon is taken out of the atmosphere in the form of carbon dioxide by plants during photosynthesis.
What happens to carbon when a primary consumer eats a plant?
When primary consumers eat a plant the following may happen to the stored carbon:
carbon compounds in the plant are digested and used to build new carbon compounds which are stored in the animal's tissues
some of the carbon compounds may be used by the consumer in respiration, releasing carbon dioxide into the atmosphere
How is carbon returned to the atmosphere in the carbon cycle?
Carbon is returned to the atmosphere when it is released as carbon dioxide by the following processes:
respiration in plants and animals
respiration in decomposers, e.g. bacteria
combustion of fossil fuels or other organic matter, e.g. wood
reversal of the dissolving process by which carbon dioxide dissolves in the oceans
What is the role of combustion in the carbon cycle?
Combustion releases carbon dioxide into the atmosphere. This occurs during the combustion of fossil fuels, or of other organic matter such as wood.
True or False?
Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere.
True.
Fossil fuel use releases carbon dioxide into the atmosphere by the process of combustion. This raises the atmospheric carbon dioxide concentration.
What is the impact of mass deforestation on the carbon cycle?
Mass deforestation (cutting down many trees) affects the carbon cycle as follows:
it reduces the number of trees carrying out photosynthesis so less carbon is removed from the atmosphere
it is often followed by combustion as trees are burned, increasing the addition of carbon to the atmosphere
Why is nitrogen needed by living organisms?
Nitrogen is required by living organisms to make proteins.
True or False?
Plants and animals can absorb nitrogen gas directly from the air.
False.
Neither plants nor animals can absorb nitrogen gas (N2) from the air. N2 needs to be fixed to produce nitrates before nitrogen can be absorbed by plants and passed on to animals.
In what form do plants absorb nitrogen from the soil?
Plants absorb nitrogen from the soil in the form of nitrates.
How is nitrogen gas converted into a usable form during the nitrogen cycle?
Nitrogen gas can be converted into a usable form as follows:
nitrogen-fixing bacteria convert N2 gas into ammonium compounds, which can then be converted to usable nitrates
lightning can split the bond between the two N atoms, turning them into nitrous oxides that dissolve in rainwater and leach into the soil
How do animals obtain the nitrogen they need?
Animals get the nitrogen they need from plant proteins or from the tissues of other animals when they eat.
True or False?
The action of decomposers returns nitrogen to the soil in the nitrogen cycle.
True.
Decomposers break down proteins in the dead and waste material, allowing nitrogen to return to the soil.
True or False?
Denitrifying bacteria increase the availability of soil nutrients.
False.
Denitrifying bacteria take nitrates out of the soil and convert them back into nitrogen gas, reducing soil fertility and plant growth.
Why do farmers often need to use fertilisers to aid crop growth?
Farmers often need to use fertilisers because harvesting crops can disrupt the nitrogen cycle. The nitrogen contained within the tissues of crop plants is not returned to the soil by decomposition, so fertilisers are needed to replace lost nitrates (as well as other minerals).
What is the purpose of crop rotation in agriculture?
The purpose of crop rotation is to reduce the problem of soil depletion. Different crops have different nutrient requirements, so growing different crops each year means that the same nutrients are not constantly being removed from the soil.
Farmers can also introduce crops that aid soil fertility into crop rotation, e.g. legumes with nitrogen fixing bacteria in their root nodules.
Define the term decomposition.
Decomposition is the break down of organic material by, e.g. bacteria and fungi.
What are the factors that impact the rate of decay?
The rate of decay is influenced by:
temperature
water availability
oxygen availability
pH can also affect the activity of decomposers.
Why does oxygen availability impact the rate of decay?
Oxygen availability impacts the rate of decay because decomposers require oxygen for respiration. If oxygen levels become depleted decomposers will die and decomposition will slow down or stop.
True or False?
In the UK decomposition happens faster in the summer than in the winter months.
True.
Higher temperatures increase the rate of decay. This is because the enzyme controlled reactions required for decomposition occur faster at higher temperatures.
True or False?
Dried foods can be preserved for longer because of their reduced water content.
True.
Water availability is low inside dried foods, meaning that conditions are not favourable for the growth of the microorganisms that cause decay.
How does vacuum-packing aid food preservation?
Vacuum-packing aids food preservation because it removes oxygen from the storage environment. This means that decay organisms cannot respire.
Why does compost develop more quickly inside insulated compost bins?
Compost develops more quickly inside insulated compost bins because insulation retains heat energy, raising the temperature of the compost heap. This allows the enzyme-controlled reactions of decay to occur more quickly.
How can the rate of decay be calculated?
The rate of decay can be calculated using the formula:
rate of decay = mass lost ÷ time taken