RP 6 - Photosynthesis

• What is photosynthesis?

  The process by which plants synthesize glucose using light energy from the Sun
• How would you investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant?

  • Place cut pondweed in a boiling tube with sodium hydrogen carbonate solution at a fixed distance from a light source
  • Count the number of bubbles produced in one minute using a stopwatch
  • Repeat several times at different distances/light intensities and calculate a mean for each distance
  • Plot a graph of light intensity (x) against rate of photosynthesis (bubbles per minute, y)
• Why is it best to use an LED light source rather than a lamp in photosynthesis experiments?

  A lamp emits more heat energy than an LED, which may change the temperature of the experiment and affect the rate of photosynthesis
• What is the relationship between the distance from a light source and light intensity?

  The relationship is described by the inverse square law: light intensity ∝ 1 / distance²
• How can the measurement of oxygen production be made more accurate in photosynthesis experiments?

  By placing the pondweed under a filter funnel with an inverted measuring cylinder over the spout to determine the volume of oxygen produced
• Why is sodium hydrogen carbonate solution used during the photosynthesis experiment?

  It releases CO₂, which is used by the pondweed during photosynthesis
• Why can the number of bubbles produced be used to calculate the rate of photosynthesis?

  Oxygen bubbles are formed as a product during photosynthesis, and the number of bubbles produced in a given time is proportional to the rate of photosynthesis