Energy Transfers In & Between Organisms

• Describe what happens during photoionization in the light-dependent reaction?

  1. Chlorophyll absorbs light
  2. Electrons are lost
• Describe the method used when separating pigments after a solution of pigments is applied to the origin line?

  1. Level of solvent below origin line
  2. Remove before solvent reaches top
• Suggest and explain the advantage of of having different coloured pigments in leaves?

  1. Absorb different wavelengths of light for photosynthesis
• Why does a decrease in the light-dependent reaction lead to a decrease in the light-independent reaction?

  1. Less ATP
  2. Less reduced NADP
• Explain why a decrease in the activity of rubisco would limit the rate of photosynthesis?

  1. Less carbon dioxide reacts with RuBP
  2. Less GP
• Where precisely is rubisco found in a cell?

  1. Stroma
• In natural ecosystems, most of the light falling on producers is not used in photosynthesis. Suggest 2 reasons why?

  1. Light is reflected
  2. Light is the wrong wavelength
• Name 2 products of the light-dependent reaction that are necessary for the light-independent reaction?

  1. ATP
  2. Reduced NADP
• How does a reduction of transfer of electrons down the electron transfer chain lead to a reduced rate of photosynthesis?

  1. Reduced chemiosmotic gradient/protein gradient across thylakoid membrane
  2. Less ATP produced
  3. Less NADPH produced
  4. Light-independent reaction slows
• Describe the process of glycolysis?

  1. Phosphorylation of glucose using ATP
  2. Oxidation of triose phosphate to pyruvate
  3. Net gain of 2 ATP
  4. NAD reduced
• Malonate inhibits a reaction in the Krebs cycle. Explain why malonate would decrease the uptake of oxygen is a respiring cell?

  1. Less reduced NAD
  2. Oxygen is the terminal electron acceptor
• Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration?

  1. Regenerates NAD
  2. So glycolysis continues
• During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how?

  1. Carbon dioxide combines with ribulose biphosphate, catalysed by rubisco
  2. Produces 2 molecules of glycerate 3-phosphate
  3. GP reduced to triose phosphate
  4. Using reduced NADP and energy from ATP
  5. Triose phosphate converted to glucose
• In the light dependent reaction of photosynthesis, light energy generates ATP. Describe how?

  1. Light energy excites electrons in chlorophyll
  2. Electrons pass down electron transfer chain
  3. Electrons reduce carriers
  4. Energy released
  5. ATP generated from ADP and (inorganic) phosphate
• Describe the fate of reduced NAD in aerobic respiration?

  1. Reduced NAD from glycolysis enters the mitochondria
  2. Moves to inner membrane of mitochondria
  3. Becomes oxidised NAD as electrons are transferred to the ETC
  4. Hydrogen ions pumped into membrane space
  5. NAD returns to Krebs cycle
• Describe the role of saprobionts in the nitrogen cycle?

  1. They use enzymes to decompose protein/RNA/DNA
  2. Producing ammonium compounds
• Describe how you would obtain a quantitative measure of cloudiness in a river?

  1. Use of colorimeter
  2. Measure the absorbance of light
  3. Standardisation, same volume of water
• Give 2 examples of biological molecules containing nitrogen that would be removed when a crop is harvested?

  1. Amino acid/protein
  2. DNA
• Why do leguminous plants need to absorb fewer nitrogen-containing compounds from the soil than other plants?

  1. Contain nitrogen fixing bacteria in root nodules
  2. Bacteria produce nitrogen-containing compounds for the plant's cells to use directly
• Describe the process of ammonification?

  1. Saprobionts
  2. Decompose nitrogen-containing compounds into ammonia (using oxygen)
• Why is the nitrate content of water logged soil low? Suggest how farmers could overcome this?

  1. Water fills the air spaces in the soil, reduces oxygen levels in soil
  2. Encourages denitrification
  3. Aerate soil and ensure good drainage
• Explain why soil in tropical rain forests contain more nitrates than the desert?

  1. Lots of thunderstorms/lightning in the tropical rainforest
  2. Provides electrical energy to react O2 and N2 to form nitrogen oxides
  3. Nitrogen oxides dissolve in rain to form nitrates in the soil
• Explain why farmers aerate their soil by ploughing their fields?

  1. More oxygen in soil so aerobic conditions
  2. Nitrifying bacteria and nitrogen fixing bacteria are aerobic, both increase nitrate content in soil
  3. Denitrifying bacteria are anaerobic, convert nitrates to nitrogen
• Nitrate from fertiliser applied to crops may enter ponds and lakes. Explain how nitrate may cause the death of fish in fresh water?

  1. Growth of algae/algal bloom blocks light
  2. Reduced photosynthesis so (submerged) plants die
  3. Saprobiotic bacteria aerobically respire
  4. Less oxygen for fish to respire/aerobic organisms die