topic 5 xoxo

• What are the 5 key limiting factors of photosynthesis?

  1. Light intensity
  2. Temperature
  3. Avaliability of water
  4. Avaliability of chlorophyll
  5. Avaliability of CO
• What is meant by 'compensation point'?

  • No net exchange of gases
  • Rate of photosynthesis is equal to the rate of respiration 
• Suggest how water stress could affect the rate of photosynthesis in a plant.

  • Plants don't have enough water - stomata will close to save the little water that they have
  • Less CO2 will enter
  • Slower rate of Calvin Cycle (less CO2 to combine with RuBP)
• Describe the role of saprobionts in the nitrogen cycle

  Producing/releasing ammonia/ammonium ions

   decompose proteins
• Describe how you would obtain a quantitative measurement of their cloudiness

  1. Use of colorimeter
  2. Measure the absorbance/transmission (of light)
  3. Examples of how the method can be standardised eg same volume of water, zeroing colorimeter, and same wavelength of light.
• Net primary production


  the chemical energy stored in plant biomass after respiratory losses to the environment have been taken into account.
• The diagram shows Melvin Calvin’s Lollipop experiment for identifying the products of the Calvin Cycle. Why was radioactive hydrogen carbonate supplied to the algae?

  So that the substances into which the CO2 is incorporated can be identified.
• The diagram shows Melvin Calvin’s Lollipop experiment for identifying the products of the Calvin Cycle. Why is a fast flow tap used in this experiment?

  To terminate the reactions immediately.
• The diagram shows Melvin Calvin’s Lollipop experiment for identifying the products of the Calvin Cycle. Why is hot methanol supplied to the algae?

  High temp will denature enzymes that catalyse reactions.

  Methonal could denature the enzymes.
• Heat stress decreases the LDR - why does this lead to a decrease in the LIDR?

  Less ATP

  Less reduced NADP