Exam qs

• Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water (5)

  • growth of algae / algal bloom blocks light
  • reduced /no photosynthesis so plants die
  • saprobiotic (microorganisms / bacteria)
  • aerobically respire/use oxygen in respiration
  • less oxygen for fish to respire /aerobic organisms die
• Explain how the NPP in the leaves of trees is made available to other plants in a rainforest ecosystem. (2)

  • ​Saprobiotic bacteria
  • ​break down dead material to release ammonia/ammonium ions
• Nitrogen and phosphorus are two elements that need to be recycled within ecosystems. ​Name two biological molecules containing nitrogen and two biological compounds ​containing phosphorus. (2)

   

  • ​Nitrogen – ATP, DNA, amino acids, proteins
  • Phosphorus – DNA, ATP, Phospholipids

   
• Suggest why natural fertilisers release their nutrients over a longer time ​period than artificial ​fertilisers. (2)

  • ​Natural fertilisers need to be broken down as they contain lots of organic matter
  • ​Artificial fertilisers contain minerals in a useable form

   
• What is the difference between nitrification and nitrogen fixation? (1)

   

  • ​Nitrification is the conversion of ammonium ions into nitrites and then nitrates
  • ​Nitrogen fixation is the conversion of nitrogen to ammonia/ammonium ions

   
• Explain how the nitrogen contained in dead animals and plants is returned to atmospheric nitrogen. (5)

  • ​Saprobiotic bacteria
  • Break down proteins in dead material to release ammonium ions
  • Ammonium ions converted to nitrites and nitrates
  • By nitrifying bacteria / Nitrification
  • ​Nitrates converted to nitrogen
  • ​By denitrifying bacteria
• Describe the role of saprobionts in the nitrogen cycle (2)

  • use enzymes to decompose proteins / DNA / RNA / urea
  • releasing ammonium ions
• Eutrophication can cause water to become cloudy.

  You are given samples of water from three different rivers.

  Describe how you would obtain a quantitative measurement of their cloudiness. (3)

  • Use of colorimeter
  • Measure absorbance / transmission of light
  • Standardise method by zeroing the colorimeter
• Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions.

  Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively in nitrate irations of ammonium compounds and low concentrations of nitrite ions (2)

  • Less nitrification
  • Less oxidation of ammonium ions to nitrite ions and to nitrate ions
  • More denitrification
  • So more nitrate ions reduced to nitrogen gas