4.3 Cycles within ecosystems Flashcards
carbon cycle
the cycle where carbon moves between organisms and the environment, namely in the form of carbon dioxide and involving:
respiration
photosynthesis
fossilisation
combustion
decomposers in the nitrogen cycle
organisms that release enzymes that catalyse the breakdown of dead plant and animal material
releasing nitrogen containing compounds such as ammonia into the soil
Combustion
when fossil fuels are burnt
- releases carbon dioxide into the atmosphere
nitrogen fixation
the process by which atmospheric nitrogen in the air is converted to nitrates and ammonia in the soil.
Nitrogen fixation happens in two ways:
Via lightning - lightning converts atmospheric nitrogen directly into nitrates
Via nitrogen-fixing bacteria - these convert atmospheric nitrogen into ammonia
Nitrification
Nitrification is carried out by nitrifying bacteria in the soil, and consists of two steps:
Ammonia in the soil is first converted to nitrites.
Those nitrites are then converted to nitrates.
What happens to nitrates after being absorbed by plant roots?
they are combined with carbohydrates (from photosynthesis)
to form amino acids which are then made into proteins, and nucleotides which are joined to make DNA and RNA
What happens when animals eat plants?
they digest the proteins and DNA, absorbing the small soluble molecules (amino acids ad nucleotides)
these are then used by the animal to synthesise new proteins and DNA (assimilation)
What happens when a plant or animal dies?
its tissues are decomposed by bacteria and fungi (saprotrophic nutrition)
What happens to the molecules containing nitrogen such as proteins?
broken down by the bacteria and fungi and ammonia is released into the soil
deritrification
In denitrification, denitrifying bacteria in the soil convert nitrates back into atmospheric nitrogen.
denitrifying bacteria
bacteria that convert nitrates in the soil into nitrogen gas
occurs when conditions are anaerobic and can be prevented by ploughing the soil –> ensures there is enough oxygen to prevent the growth of these organisms
nitrifying bacteria
aerobic organisms that convert ammonia to nitrites and then nitrates which can be absorbed by plants using active transport
nitrogen cycle
the cycle through which nitrogen moves between living organisms and the environment
nitrogen fixing bacteria
bacteria that convert nitrogen gas into nitrogen containing compounds that plants can use
- can be free living in the soil or found in root nodules of leguminous plants
What is the name of the process that converts nitrates to atmospheric nitrogen?
Denitrification
Which process describes how plants use nitrogen to build biological molecules?
Assimilation
Where is nitrogen-fixing bacteria found?
soil
roots of some plants
Assimilation
Assimilation is the process by which plants absorb nitrates and ammonium ions, and use them to create biological molecules such as proteins. These biological molecules form part of the plant’s tissues.
When animals eat plants they assimilate these nitrogen containing compounds (e.g. proteins) into their own bodies
Decomposition
Decomposition occurs when decomposers feed on the waste excretions of animals, and the rotting corpses of dead plants and animals. During this process they convert urea and proteins into ammonia.
The ammonia in the soil forms ammonium ions, which is one of few the nitrogen-containing compounds plants can absorb and assimilate
Why is denitrification bad for plants?
Denitrification is bad for plants because it means there are fewer nitrates in the soil, reducing the amount available for the plants to absorb and assimilate.
