Nutrient Cycles Flashcards
Ammonification
The production of ammonia from organic ammonium containing compounds (eg. urea, nucleic acids and vitamins) through feeding by Saprobiotic microorganisms
Nitrification
Conversion of ammonium ions to nitrate ions by oxidation of ammonium ions to nitrite ions and nitrite ions to nitrate ions by nitrifying bacteria
Why is ploughing important?
Nitrifying bacteria require oxygen to carry out nitrification so soil must be kept light and well aerated. Good drainage also prevents air spaces from being filled with water, preventing air being forced out of the soil.
Nitrogen Fixation
The process by which nitrogen gas is converted into nitrogen-containing compounds
What are the two types of nitrogen fixing microorganisms?
- free-living nitrogen-fixing bacteria
- > reduce gaseous nitrogen to ammonia which they then use to manufacture amino acids
- > Nitrogen-containing compounds are released when they die and decay - mutualistic nitrogen-fixing bacteria
- > live in nodules on the roots of plants such as peas and beans
- > They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria
Denitrification
Conversion of soil nitrates into gaseous nitrogen by denitrifying bacteria.
Why are fertilisers necessary in agricultural systems?
The crop harvested is transported from its origin for consumption so the urine, faeces and dead remains of the consumer are rarely returned to the same area of land, reducing the mineral ion concentration.
Natural organic fertilisers
Consist of the dead and decaying remains of plants and animals as well as animal wastes such as manure and bone meal.
Artificial inorganic fertilisers
Mined from rocks and deposits and then converted into different forms and blended together to give appropriate balance of minerals for a particular crop. Compounds almost always contain nitrogen, phosphorus and potassium.
How do nitrogen fertilisers reduce species diversity?
Nitrogen-rich soils favour the growth of grasses and other rapidly growing species, which out compete many other species which die as a result.
What does leaching involve?
The process by which rain water dissolves soluble nutrients such as nitrates, carrying them deep into the soil beyond plant roots into watercourses, such as rivers and streams, into fresh water lakes. This can be harmful if the the lake is a source of drinking water. Very high nitrate levels in drinking water can prevent oxygen transport in babies and a link to stomach cancer has been suggested.
Eutrophication
- Nitrate is typically a limiting factor for algae and plant growth in the body of water
- As nitrate conc. increases as a result of leaching, plants and algae grow exponentially
- The surface of the water becomes densely populated with algae - ‘algal bloom’
- Algal bloom prevents light from penetrating to lower depths of water
- Algae and plants below the surface of the water die due to lack of photosynthesis
- Saprobiotic algae feed of the dead algae and plant matter to grow exponentially
- As the population of saprobiotic organisms increase, a higher demand for oxygen is created by respiration causing oxygen conc. to reduce
- Aerobic organisms in the body of water such as fish die due to lack of oxygen
- The lack of competition for anaerobic organisms cause their population to rise
- The anaerobic organisms further decompose the dead material, releasing toxic waste such as hydrogen sulfide making the water putrid
What are the consequences of global warming?
- Melting of polar ice caps -> extinction + rise in sea level
- Rise in sea level could flood low-lying land + major cities
- Salt water would extend further up rivers and make cultivation of crop plants difficult
- Higher temperatures and less rainfall could lead to the failure of the present crop in some areas
- Distribution of plants and animals would change in favour of those adapted to withstand new conditions -> prevalence of xerophytes
- Life cycles and population of insect pests would alter as they adapt to changed conditions -> tropical diseases could spread to the poles
What are the possible benefits of global warming?
Increased rainfall would fill reservoirs, warmer temperatures would allow crops to be grown where it’s presently too cold, the rate of photosynthesis could increase and it might be possible to harvest twice a year.
How are carbon-containing compounds present in leaves that fall from a free used for growth by microorganisms in the soil?
Saprobiotic microorganisms secrete enzymes on dead organisms. These enzymes break down complex molecules into smaller soluble molecules that are then absorbed by diffusion.
