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My name is Poon Cheng Moh. I have been teaching biology in SMK(P) Raja Zarina, Port Klang for 26 years. I sincerely hope that this blog on SPM Biology will be useful to both teachers and students.

Saturday, September 10, 2011

Answers to Hands on Pg 74


To show that light is needed for photosynthesis


Is light needed for photosynthesis?


Plant needs light for photosynthesis.


Manipulated: Presence or absence of sunlight

Responding: Presence or absence of starch

Fixed: Temperature, light intensity, concentration of carbon dioxide


Materials: Ethanol, iodine solution, aluminium foil and paper clips

Apparatus: Beaker, boiling tubes, Bunsen burner, tripod stand, wire gauze and white tile


Test for starch in leaf using iodine solution and draw the diagram of the leaf to show the part of the leaf that turned dark blue.


1. Keep a plant in the dark for two days.

2. Choose a healthy leaf on the plant and cover part of a leaf with the aluminum foil as shown.

3. The plant was exposed to sunlight for 6 hours.

4. Light the Bunsen burner and boil the water. When the water had boiled add the leaf.

5. Wait one minute for the leaf to boil (this is to get rid of the waterproof layer and break the open cells and make it soft).

6. Turn off the Bunsen burner (for safety reasons, we are going to use ethanol), and take out the leaf.

7. Put the leaf in a boiling tube and cover with ethanol.

8. Be careful when using ethanol because its highly flammable.

9. Put the tube of ethanol plus leaf into the beaker of hot water.

10. Dip the leaf back into the hot water so it can get the ethanol off.

11. Spread the leaf out on a tile.

12. Add about five drops of iodine on to the leaf and observe after about two minutes after the iodine had soaked in.

13. Draw the diagram of the leaf to show the part of leaf that turned dark blue.

14. Repeat steps 4-13 on another leaf (not covered) on the same plant.


Diagram after experiment


Hypothesis is accepted. Light is needed for photosynthesis.

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