Photosynthesis Experiments

Question 1

Testing a leaf for starch

Answer 1

1. Heat leaf in boiling water for 10 seconds to denature the enzymes and stop chemical reactions
2. Put the leaf into a test tube of alcohol. Stand test tube in the beaker of hot water for 10 mins. This will decolourise the leaf
3. Rinse leaf in water to remove alcohol and rehydrate it
4. Put leaf in white tile cover with iodine solution
   A blue/black colour shows that starch is present

Question 2

Test for chlorophyll (whether it is needed for photosynthesis)

Answer 2

1. Take a variegated leaf from a plant that has been exposed to light. Record which parts were green and which parts weren’t
2. Test the leaf for starch - only parts that were green turn blue-black
   This suggests that only parts of the leaf that contained chlorophyll are able to photosynthesise and produce starch

Question 3

Test for CO2 (whether it is needed for photosynthesis)

Answer 3

1. Set up experiment with a soda lime and plant inside a sealed bell jar. A lamp shines light at the apparatus
2. The soda lime will absorb CO2 out of the air in the jar
3. After being left for a while and tested for starch, the plant leaves won’t turn blue-black
   No starch made in the absence of CO2 = CO2 needed for photosynthesis

Question 4

Test for light (whether it is needed for photosynthesis)

Answer 4

1. Place plant in dark cupboard for 48 hours. This will mean that it has used up its starch stores
2. Cut a leaf from the plant and test it for starch using iodine solution. The leaf will not turn blue-black.
   Therefore, light is needed for photosynthesis