Photosynthesis

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Test for Starch in a Leaf

Equipment:  Beaker, heat-proof mat, tripod, bunsen, gauze, test tube, pipette, leaf, ethanol, tile and iodine solution

 Method:

1.     Boil water and place it in the beaker.

2.     Place it on top of a gauze on a tripod. Place the Bunsen burner under on heatproof mat.

3.     Place a leaf in the water to kill it and stop photosynthesis. Leave for 1 minute

4.     Then place the leaf a test tube of ethanol and place that in the hot water for 10 minutes. Turn off the Bunsen. This extracts the chlorophyll and makes the colour change more obvious

5.     Place the leaf back in the hot water for another minute. This softens the leaf so it can be spread out on the tile.

6.     Spread the leaf out on a tile.  Cover in iodine solution.

8.     If starch is present it will turn blue-black if not it will remain orange.

1 of 4

Does a plant need light to carry out p/s?

Two conditions – light and dark

·      Leave for 48 hours

·      Test for starch

·      Leaf in light blue-black

·      Leaf in dark orange

Precautions: to remove starch leave plant in dark for 48 hrs before. Starch will be used up in respiration.

2 of 4

Does a plant need CO2 to p/s?

 Two conditions – CO2 and no CO2(leave in bag of NaOH to absorb the CO2)

  •  Leave for 48 hours
  • Test for starch
  • Leaf in CO2 blue-black
  • Leaf not in CO2 orange

Precautions: to remove starch leave plant in dark for 48 hrs before. Starch will be used up in respiration.

3 of 4

Does a plant ned chlorophyll to p/s?

Two conditions – Chlorophyll present (green part of leaf) and no chlorophyll (white part of leaf)

  • Leave in light for 48hrs
  • Green bit will turn blue-black with iodine
  • White bit will remain orange with iodine

Precautions: to remove starch leave plant in dark for 48 hrs before. Starch will be used up in respiration.

4 of 4

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