pondweed required practical

• 1. Leave for five minutes for the pondweed to acclimatise to the new light intensity.
  2. Count the number of bubbles given off in one minute.
  3. Move the light 10 cm further back.
  4. Leave for five minutes for the pondweed to acclimatise again.
  5. Count the number of bubbles given off in one minute.
  6. Repeat by moving the lamp away by 10 cm intervals until 50 cm is reached.
• the pondweed experiment is done to see how light intensity affects the rate of photosynthesis
• the independent variable (what we change) for the pondweed experiment is the light intensity (how close the light is)
• the dependant variable (what we measure)for the pondweed experiment is the amount of bubbles given off to show the rate of photosynthesis
• the control variable (what we keep the same) for the pondweed experiment is the size of the pondweed, the temperature of water and its volume
• the results of the pondweed experiment should suggest that the further away the pondweed is from the lamp the lower the rate of photosynthesis
• in the pondweed experiment more oxygen bubbles are produced when the light is closer to the beaker. So a greater light intensity gives a greater rate of photosynthesis.
• we can measure the rate of photosynthesis by counting the bubbles that are produced by the pondweed
• we can add a heat shield to the apparatus to control the temperature of the pondweed
• as the distance of the light from the plant increases the light intensity decreases this is called an inverse relationship. the light intensity changes inversely to the square of the distance
• the inverse square law can be calculated using the equation I = 1/d^2