Photosynthesis

• Why is an LED light source preferred for this experiment?


  Because it doesn't release much heat
• What should you do if using a normal light bulb instead of an LED?

  Place a beaker of water between the light and the boiling tube
• What solution is filled in the boiling tube for the experiment?


  Sodium hydrogen carbonate solution
• What does sodium hydrogen carbonate solution release that is needed for photosynthesis?


  Carbon dioxide
• What should be placed in the boiling tube with the sodium hydrogen carbonate solution?

  A piece of pond weed
• How long should the pond weed be left to acclimatize in the boiling tube?

  Five minutes
• What gas is produced by the pond weed during photosynthesis?

  Oxygen
• What should you do after starting the stopwatch during the experiment?

  Count the number of bubbles produced in one minute
• How many times should the experiment be repeated to calculate the mean number of bubbles produced?

  Two more times
• What are two main problems with counting bubbles in this practical?

  The bubbles can be too fast to count accurately and vary in size
• How can the problems with counting bubbles be solved?

  By measuring the volume of oxygen produced instead of counting bubbles
• What equipment is used to measure the volume of oxygen produced?

  A measuring cylinder filled with water
• What happens to the number of bubbles per minute when the distance from the light source is doubled?

  The number of bubbles per minute falls by a factor of four
• What is the scientific term for the relationship between distance and light intensity in this experiment?

  The inverse square law
• Why does doubling the distance cause the light intensity to fall by four times?

  Because light intensity decreases with the square of the distance
• What is necessary for photosynthesis that affects the number of oxygen bubbles produced?

  Light
• Independent variable 


  Light intensity (distance of lamp from plant)
• Dependant variable


  The number of oxygen bubbles produced per minute and volume of oxygen produced per minute.
• Control variable


  type, mass or length of plant, power of lamp, temperature (measure with thermometer), co2 concentration (add sodium bicarbonate solution to increase this) ANY OF THESE COUL BE IV
• What do green plants use to produce glucose and oxygen during photosynthesis?

  Carbon dioxide and water in the presence of light energy
• What factors can affect the rate of photosynthesis in the practical experiment?

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• What type of plant is used in the photosynthesis practical?

  Aquatic plant, specifically common pond weed
• Why is sodium hydrogen carbonate solution added to the boiling tube?

  To encourage the pond weeds to photosynthesize
• How is the oxygen produced by the pond weed measured in the experiment?

  By counting the number of bubbles of oxygen gas released
• Why is the stem of the pond weed cut underwater?

  To ensure a steady stream of oxygen bubbles is produced
• What is the independent variable in the photosynthesis experiment?

  Light intensity
• How can light intensity be changed in the experiment?

  By changing the distance between the pond weed and the light source
• Why is it suggested to use an LED light source instead of a regular bulb?

  LEDs produce less heat, preventing temperature changes
• What should be done before taking measurements of oxygen bubbles?

  Allow the pond weed to adjust to the light for a few minutes
• How many values should be recorded for the independent variable in the experiment?

  Five values
• What happens to the number of bubbles produced as the distance from the light source increases?

  The number of bubbles produced decreases
• What is an alternative method to measure oxygen production in the experiment?

  • Collect the gas produced using a glass funnel and boiling tube
  • Measure the volume of oxygen collected
  • Test with a glowing splint to confirm it is oxygen
• What is the purpose of inverting the boiling tube over the funnel in the alternative method?

  To collect the oxygen gas produced by the pond weed
• What indicates that the gas collected is oxygen in the alternative method?

  A glowing splint relights when exposed to the gas
• What is the role of light energy in photosynthesis?

  It is necessary for the conversion of carbon dioxide and water into glucose and oxygen.
• Why is it important to control variables in the photosynthesis experiment?

  To ensure that the test is fair and results are valid.
• Why is the pond weed cut at an angle?

  To ensure a steady stream of oxygen bubbles is produced.
• Why is it necessary to turn off overhead lights during the experiment?

  To ensure that the only light source is from the lamp being used.
• What is the potential error in assuming all bubbles produced are the same volume?

  It may lead to inaccurate measurements of oxygen production.
• What is the setup for collecting gas in the alternative method?

  A glass funnel is placed under the pond weed in a beaker of water.