1. What is the role of saprobionts in decomposition ?
Answer
Carry out extracellular digestion, releasing phosphate ions and ammonium compounds.
2. The figure below shows a simplified diagram of the nitrogen cycle. Identify what is represented by X in the diagram.
Answer
Nitrite ions (NO2–)
3. Give the letter(s) of the arrows that represent ammonification and nitrification.
Answer
ammonification - E,
4. Describe the role played by microorganisms in stage A and stage I.
Answer
Stage A (Nitrogen fixation): Nitrogen-fixing bacteria play a crucial role by converting atmospheric nitrogen gas into ammonia or ammonium ions. This process makes nitrogen available in a form that plants can absorb and use for growth.
Stage I (Denitrification): Denitrifying bacteria are responsible for converting nitrates and ammonium compounds back into nitrogen gas or oxides of nitrogen. This returns nitrogen to the atmosphere, completing the nitrogen cycle.
5. Name some nitrogen-containing molecules that are found in plants and animals.
Answer
Proteins, DNA, RNA, ATP, amino acids, nucleotides, etc.
6. In sewage treatment works, sewage enters large tanks. The organic matter settles at the bottom of the tank and is then placed into a large fermenter. In the fermenter, anaerobic bacteria digest the organic matter into biogas, which is high in methane. The sewage sludge that remains can be used as fertiliser on farmland. Suggest some advantages of carrying out this process in a fermenter rather than in an open tank.
Answer
Methane/biogas can be collected, does not contribute to global warming, open tank is a potential safety hazard to personnel, etc.
7. Give some advantages of using treated sewage sludge on farmland, rather than inorganic fertiliser.
Answer
Breaks down more slowly over longer time, adds organic matter to soil improving soil quality, could cause pollution if not used on farmland, inorganic fertiliser more likely to leach/cause eutrophication, etc.