Plant Nutrition ( 2 )

• Chlorophyll is needed for photosynthesis because it helps absorb light
• Light is important for photosynthesis because it provides the energy to drive the reaction
• Carbon dioxide is important for photosynthesis because it is converted into sugars such as glucose
• Investigating the importance of factors for photosynthesis

  1. Get a functioning plant

  2. Deprive it of each factor individually

  3. Prove the plant stops photosynthesizing when factors are absent
• Starch is stored in chloroplasts where photosynthesis occurs, so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesizing
• Glucose is not reliable to test for because it is quickly used, converted into other substances, and transported or stored as starch
• Removing starch and chlorophyll from leaves before investigations


  1. Leave plants in dark for 48 hours to use up starch

  2. Boil leaves in water to make permeable

  3. Boil leaves in ethanol to remove chlorophyll

  4. Rinse leaves in water to soften
• Investigating the need for chlorophyll in photosynthesis

  1. Use a variegated leaf

  2. Boil leaf in water to kill cells and break down membranes

  3. Put leaf in hot ethanol for 5-10 minutes to remove chlorophyll

  4. Dip leaf in boiling water to soften

  5. Spread leaf on white tile and add iodine solution
• Areas of leaf with no chlorophyll


  Do not turn blue-black when tested with iodine, indicating no starch and no photosynthesis
• Investigating the plant's need for light in photosynthesis

  1. Destarve plant by leaving in dark for 48 hours

  2. Partially cover leaf with aluminum foil

  3. Place plant in sunlight for a day

  4. Prepare leaf and test with iodine
• Covered area of leaf

  Does not turn blue-black with iodine, indicating no starch and no photosynthesis
• Investigating if carbon dioxide is needed for photosynthesis

  1. Destarve two plants by leaving in dark

  2. Place one plant in bell jar with sodium hydroxide to absorb CO2

  3. Place other plant in bell jar with water as control

  4. Place both in bright light

  5. Prepare leaves and test with iodine
• Leaf from plant near sodium hydroxide

  Does not turn blue-black with iodine, indicating no starch and no photosynthesis due to lack of CO2
• Factors affecting rate of photosynthesis are light intensity, carbon dioxide concentration, and temperature
• Investigating effect of light intensity on rate of photosynthesis

  1. Use aquatic plant in beaker of water with sodium hydrogen carbonate

  2. Place inverted funnel on plant and inverted boiling tube on funnel

  3. Use thermometer to monitor temperature

  4. Place lamp at different distances from beaker to vary light intensity

  5. Calculate rate of photosynthesis from oxygen bubbles released
• Increasing light intensity


  Increases rate of photosynthesis until another factor becomes limiting
• Investigating effect of carbon dioxide concentration on rate of photosynthesis

  1. Similar setup to light intensity experiment

  2. Vary amount of sodium hydrogen carbonate dissolved in water to change CO2 concentration

  3. Keep light intensity constant
• Increasing carbon dioxide concentration

  Increases rate of photosynthesis until another factor becomes limiting
• Investigating effect of temperature on rate of photosynthesis

  1. Similar setup to previous experiments

  2. Use hot plate to heat solution and vary temperature

  3. Calculate rate of photosynthesis at different temperatures
• Increasing temperature


  Initially increases rate of photosynthesis until optimum, then decreases due to enzyme denaturation