Practical: Rate

• What is the purpose of the practical investigating photosynthesis?

  To determine factors affecting photosynthesis rate
• Which aquatic plants can be used in the investigation?

  Elodea or Cabomba
• How can light intensity be changed in the experiment?

  By changing the distance from the light source
• What does sodium hydrogencarbonate produce when dissolved?

  Carbon dioxide (CO₂)
• How should temperature be controlled during the experiment?

  By using water baths of different temperatures
• What must remain constant when changing one factor in the investigation?

  The other two factors being tested
• Why should the pondweed be submerged in sodium hydrogen carbonate solution?

  To ensure a controlled supply of carbon dioxide
• What is measured to assess the rate of photosynthesis?

  The volume of gas collected
• What is the relationship between light intensity and oxygen production?

  Higher light intensity increases oxygen production
• How can temperature affect the rate of photosynthesis?

  By increasing the temperature of the water
• What happens to oxygen production at a certain light intensity?

  It stops changing when another factor limits it
• What is the formula for light intensity in relation to distance?

  Light intensity is proportional to $1/d^2$
• What is the role of immobilised algae beads in experiments?

  To ensure a standard quantity of algae
• Where do the light-dependent reactions of photosynthesis occur?

  In the thylakoid membrane
• What happens to electrons during the light-dependent reactions?

  They are released from chlorophyll a molecules
• What is the effect of a redox indicator like DCPIP in the experiment?

  It accepts electrons and changes color
• What color does DCPIP turn when reduced?

  Colorless
• How does light intensity affect the rate of photoactivation of electrons?

  Higher intensity speeds up photoactivation
• What is the purpose of using an isolation medium in the experiment?

  To produce a concentrated leaf extract
• Why must the isolation medium be ice-cold?

  To avoid damaging the chloroplasts
• What is the significance of controlling the temperature during the experiment?

  To maintain optimal conditions for photosynthesis
• What should be done to ensure the effect of light is measured accurately?

  A control not exposed to light should be set up
• What does a higher rate of decrease in absorbance indicate?

  Higher activity of the dehydrogenase enzyme
• What is a limitation of measuring the rate of photosynthesis using DCPIP?

  It predicts rather than directly measures activity
• What should be done to ensure accurate results in the experiment?

  Repeat results and calculate the mean value
• Why is it important to control the amount of leaf used in the experiment?

  To ensure consistent chloroplast concentration
• What are the three limiting factors of photosynthesis?

  Light intensity, temperature, carbon dioxide concentration
• How can light intensity be altered in the laboratory?

  By changing the distance between the lamp and plant
• What must be kept constant during the experiment?

  The control variables not being tested