B8

• What is a limiting factor in a chemical reaction?

  A factor in limited supply that restricts reaction rate
• What safety precautions should be taken during the photosynthesis practical?

  • Wash hands after handling pondweed
  • Be cautious of hot lamp
  • Keep electrical equipment dry
• What equipment is needed for the photosynthesis practical?

  • Pondweed
  • Scissors
  • Boiling tube of water
  • Test tube rack
  • Large beaker of water
  • Lamp
  • Metre rule
  • Stopwatch
  • Thermometer
• How long should the piece of pondweed be cut for the experiment?

  8–10 cm long
• What should be done after placing the pondweed in the boiling tube?

  Measure the temperature of the water
• How far should the lamp be placed from the boiling tube initially?

  15 cm
• How long should bubbles be counted for in the experiment?

  2 minutes
• What should be done after counting the bubbles?

  Measure the temperature again
• How should the distance between the lamp and boiling tube be changed in the experiment?

  Increase by 2 cm each time
• What should be done after repeating the experiment multiple times?

  Calculate the mean number of bubbles
• What is the role of nitrates in plants?

  Essential for producing amino acids and proteins
• What can glucose be used to make in plants?

  Starch, cellulose, proteins, and lipids
• What deficiency symptom indicates a lack of nitrates?

  Pale upper leaves and yellow lower leaves
• What is magnesium needed for in plants?

  Chlorophyll production
• What deficiency symptom indicates a lack of magnesium?

  Pale lower leaves with normal upper leaves
• How can artificial lighting benefit plant growth?

  • Increases light intensity
  • Must avoid damaging chlorophyll
• How can carbon dioxide concentrations be increased in glasshouses?

  • Using heaters that burn fossil fuels
  • Pumping CO2 into the glasshouse
• What are the advantages of using glasshouses for plant growth?

  • Controlled conditions for photosynthesis
  • Maximizes growth and profit
  • Allows multiple crops per year
• How does light intensity affect the rate of photosynthesis?

  Increases until a maximum value is reached
• What determines the overall rate of photosynthesis when multiple limiting factors are present?

  The factor in shortest supply
• What are the three main limiting factors for photosynthesis?

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• What happens to light intensity as the distance from the plant increases?

  It decreases following an inverse square law
• What happens to the rate of photosynthesis at high CO2 concentrations?

  It increases until a maximum is reached
• What happens to the rate of photosynthesis above 40°C?

  It drops to zero
• Why does the rate of photosynthesis drop at high temperatures?

  Enzymes in chloroplasts denature
• How does temperature affect the rate of photosynthesis?

  Increases proportionally until a maximum
• What role does chlorophyll play in photosynthesis?

  Absorbs light energy for the reaction
• What happens when chlorophyll levels increase in leaf cells?

  The rate of photosynthesis increases
• What is the purpose of the photosynthesis practical?

  • To observe the effect of light intensity on photosynthesis
  • Control variables: length of pondweed, temperature, CO2 concentration
• Why might results from the practical be inaccurate?

  Difficulty counting small bubbles accurately
• Why should the plant be left for a few minutes before counting bubbles?

  To allow adjustment to light and temperature
• How can heat from the lamp be minimized as a source of error?

  Use a heatproof glass screen
• What other limiting factors must be considered besides light?

  Temperature and CO2 concentration
• What happens to the rate of photosynthesis at maximum light intensity?

  It levels off due to other limiting factors
• What is the overall process of photosynthesis?

  Plants use CO2 and water to make glucose
• Where does photosynthesis occur in plants?

  In the chloroplasts
• What is required for photosynthesis to occur?

  Light energy
• What is the relationship between lamp distance and bubble production rate?

  Closer lamp increases bubble production rate