Chapter 34 - Biochemical Cycling Flashcards
What’s biochemical cycling?
The flow of chemical elements between living organisms and the environment.
What is a cycle?
When a substance is removed, used and released to be reused again.
Why is nitrogen an essential element in nature?
It is essential for growth and reproduction in plants & animals.
It’s found in amino aids that make up proteins, nucleic acids, organic compound like chlorophyll + vitamins and in inorganic substances like nitric acid + ammonia.
Why cant plants use nitrogen directly from the air?
Because 2 nitrogen atoms are held together by very strong and stable bonds, making nitrogen molecules in the air inert. In order for nitrogen to be used for plant growth, it must be fixed into a reactive form.
Name the process involved of the following microorganisms in the nitrogen cycle:
- Rhizobia (nitrogen-fixing bacteria)
- putrefying bacteria
- nitrifying bacteria
- denitrifying bacteria
- nitrogen fixation
- ammonification/decomposition/putrefication
- nitrification
- denitrification
Describe the process of biological nitrogen fixation.
Nitrogen fixing bacteria live in the root nodules of legume plants.
They convert unusable nitrogen into ammonia or ammonium compounds in aerobic conditions.
Ammonia and ammonium is then converted to amino acids which is then provided to legume cells in return for carbohydrates. The plant uses the amino acids to make proteins for growth and production of chlorophyll and nucleic acids.
Some plant roots absorbs nitrates which are used by the plant to make amino acids.
Explain the process of atmospheric nitrogen fixation.
The enormous energy of lightning breaks up nitrogen molecules and enables their atoms to bond with oxygen in the air forming nitrogen oxides.
They dissolve in rain, forming nitric and nitrous acids which combine with other salts to form nitrates.
Explain the process of industrial nitrogen fixation. (Haber process)
Under great pressure and temperature, atmospheric nitrogen and hydrogen can be combined to form ammonia
Ammonia can be used directly as fertiliser, but most of it is processed into urea and ammonium nitrate.
NPK fertilisers form nitrates when added to the soil.
Explain how animals obtain animal protein.
Plants absorb nitrates to produce protein. Animals feed on plants and take in the nitrogen in the form of proteins during nutrition. Animals digest protein into amino acids and absorb it to synthesise animal protein.
Explain the process of decomposition.
When plants and animals die, their bodies are broken down by putrefying bacteria and fungi during decomposition
This process of decomposition of nitrogenous compounds results in the formation of ammonia and ammonium compounds (ammonification).
Excretory products of plants and animals contain nitrogenous waste such as urea and uric acid, which are decomposed to form ammonia and ammonium compounds.
Faeces and animal manure are also decomposed into ammonia and ammonium compounds.
Explain the process of nitrification.
Ammonia and ammonium compounds must now be converted into nitrites.
The nitrites are then converted into nitrates by nitrifying bacteria.
Nitrification requires aerobic conditions.
Nitrate ions can be taken up and used by plants to produce protein.
Nitrifying bacteria live in the soil and use ammonia and ammonium compounds as an energy source.
Explain the process of denitrification.
Denitrifying bacteria obtain energy by breaking down nitrates into nitrogen gas which escapes into the atmosphere.
This occurs in anaerobic conditions.
Denitrification is important to maintain the cycle and to prevent nitrogen being trapped.
Why is denitrification not good for agriculture?
They reverse the action of nitrifying bacteria which isn’t good for agriculture and plant growth. Because nitrates are required for amino acids, protein and nucleic acid formation and therefore growth in plants.
Nitrogen gas isn’t a usable form for plants. Removal of nitrates slows plant growth which reduces crop yield.
Denitrification reduces the level of nitrates in the soil, therefore decreasing the fertility of the soil and fertilisers then needs to be added to the soil.
Why is carbon and essential element in nature?
It forms part of more compounds than any other element and form the basis to all plant and animal life.
Carbon is the basis of organic molecules like carbohydrates, fats & proteins.
0.04% of air is carbon dioxide.
Explain the process of photosynthesis in the carbon cycle.
Green plants remove CO2 during photosynthesis.
The carbon from CO2 is fixed into carbohydrates like glucose and starch molecules.
