c.6- nitrogen and phosphorous cycles Flashcards
describe the nitrogen cycle
- nitrogen fixation: nitrogen gas (N2) in the atmosphere is converted to ammonia (NH3) in the soil by:
- mutualistic nitrogen-fixing bacteria in root nodules (eg Rhizobium)
- free-living nitrogen-fixing bacteria in the soil (eg Azotobacter)
- non-living processes, (eg lightning and the Haber process) - nitrification of ammonia (NH3) to nitrite (NO2-) by the genus of Nitrosomonas bacteria
- nitrification of nitrites (NO2-) into nitrates (NO3-) by nitrifying bacteria (eg Nitrobacter)
- denitrification of nitrates (NO3-) into nitrogen gas (N2) in the atmosphere (eg by Pseudomonas denitrificans)
OR
- Uptake and assimilation of nitrates (NO3-) by plants, and subsequently animals.
- Ammonification into ammonia (NH3) by decomposers, (mainly bacteria and fungi)
describe the mutualistic relationship between rhizobium and roots
- plant cannot carry out nitrogen fixation by itself but it is vital for the production of amino acids
- plants passes carbohydrates produced during photosynthesis to the bacteria as an energy source
what are chemoautotrophs? give two examples
they derive energy from inorganic compounds
- nitrobacter
- nitrosomonas
when do denitrifying bacteria reduce nitrate in the soil, releasing gaseous nitrogen as a product?
in the absence of oxygen
give 2 impacts of water logging on the nitrogen cycle
- eutrophication, if the excess water flows off the field and enters water courses as a runoff
- loss of bioavailable nitrogen through denitrification by Pseudomonas denitrificans
oxygen is in —– supply in waterlogged soils
short
state an adaptation of plants living in wetlands and explain the need for it
wetlands have permanently waterlogged soils and would therefore have nitrogen-deficient soils
an adaptation of bog plants is to become insectivorous and obtain nitrogen through the extracellular digestion of animals
what is phosphorous required for in living things?
to produce molecules such as ATP, DNA, RNA, maintain skeletons, and form a component of cell membranes
define the rate of turnover
the amount of phosphorous released from one stock to another per unit time
phosphorous has a relatively —— turnover rate in comparison to nitrogen
low
why does phosphorous have a low turnover rate?
it is only slowly released from rocks into soil/ecosystems by weathering and erosion.
how can amount of phosphorous in the phosphorous cycle be changed?
- added by application of fertiliser
- removed by the harvesting of agricultural crops
how is fertiliser made?
by mining of phosphorous and conversion to phosphate-based fertiliser
how will availability of phosphate resources affect agriculture in the future?
the availability of phosphate will limit agriculture; there is a depletion of phosphate resources that can be mined. without fertilisers, famine would result as yields would plummet
describe eutrophication
- rain can result in the leaching of water-soluble nutrients from agricultural land into bodies of water
- the nutrients favour the growth of algae leading to algal bloom, blocking the light to the plants below
- when the algae and plants below them die, it leads to loss of oxygen due to bacterial activity on the dead organic matter (high BOD)
- fish die
