Describe how energy flows in an ecosystem [8] #
[ZIMSEC November 2003/2/13(a)]
- Source of energy, the sun
- Sun to plants/producers
- Conversion of light to chemical energy
- From plants/producers to primary consumers
- Examples of a food chain
- Secondary to tertiary consumers
- Loss of energy at each tropical level i.e loss of heat/respiration/excretion /egestion to the atmosphere
- Unidirectional flow of energy
Explain the role of nitrifying bacteria and denitrifying bacteria in the Nitrogen Cycle[8]. #
- nitrifying bacteria;
- convert , ammonium / NH4+ , to , nitrate III / nitrite / NO2- ; A ammonia / NH3
- nitrite , converted to , nitrate (V) / NO3- ;
- requires , aerobic conditions / oxygen / aerated soil ;
- (nitrate (V) ions) can be , taken up / used , by plants ;
- denitrifying bacteria;
- remove nitrate (V) (ions) / convert nitrate (V) (ions) to nitrogen (gas) ;
- in , anaerobic conditions / oxygen poor soil / non-aerated soil ;
- recycles nitrogen / further use of nitrogen (by fixing) ;
- prevents nitrogen being trapped
Describe the role played by microorganisms in the nitrogen cycle [6] #
[ZIMSEC June 2003/2/10(a)]
- saphrophytic bacteria/ fungi feed on dead organisms or waste/ decompose dead organisms or waste
- releasing ammonium compounds /ammonia
- nitrifying bacteria/ nitrosomonas
- oxidise ammonia or ammonium compounds to nitrates.
- oxidation of nitrates to nitrates by free-living bacteria/ nitrobacter/ nitrococcus
- nitrogen fixing bacteria/ rhizobium/ mutualistic bluegreen bacteria/ nostoc/ free- living green bacteria/ Azotobacter/ clostridium
- convert (gaseous) nitrogen into ammonia/nitrates
- denitrificans:
- converts nitrates (in the soil)into gaseous nitrogen
Discuss the use and effects of nitrogen containing fertilizers in agriculture. [8] #
[ZIMSEC November 2014/2/9(a)]
- Nitrogen containing fertilizers increase yields
- When a farmer rotate crops nitrogen containing fertilizers do not cause much harm
- When a farmer applies the correct amount of fertilizer no harm occurs;
- Problem arises when excess fertilizer are applied;
- Excess application of fertilizer causes eutrophication of water bodies;
- Eutrophication of water bodies cause algal blooms;
- Algal blooms decompose and reduce the amount of oxygen in water bodies;
- Cause death of aquatic organisms;
- Due to lack of oxygen;
