Name:____________________________________ Class:_____________________

Topic: PhotosynthesisLab Report: Testing a Leaf for the Presence of StarchDate: 6/2/13

Introduction:Photosynthesis is the process in which plants make their own food using carbon dioxide, water, sunlight and chlorophyll. Sugar (starch), which is stored in the leaves, and oxygen, are produced in this process. Sunlight is the source of energy. Chlorophyll is found in the chloroplast where photosynthesis takes place. Carbon dioxide and water are the raw materials which are turned into sugar and oxygen.

This is the word equation for photosynthesis:

SunlightCarbon dioxide + Water Sugar + Oxygen Chlorophyll

Sunlight, carbon dioxide, water and chlorophyll are needed for photosynthesis to take place. Photosynthesis cannot happen if one of these factors is missing.

Aim:To show that photosynthesis cannot take place without the presence of carbon dioxide.

Materials needed:

Leaf to be tested Beaker Test tube Iodine Ethanol Glass rod Test tube holder Forceps Water Tripod stand Bunsen Burner Wire gauze White tile

Procedure:

1. Remove a green leaf from a plant that has been exposed to sunlight for a few hours

2. Half-fill a 250cm3 beaker with water. Heat the water until it boils. Keep the water at boiling point.

3. Use the forceps to place the leaf in the boiling water. Boil for 2 minutes.4. Turn off the Bunsen burner. 5. Place the boiled leaf in a boiling tube containing ethanol.6. Place the boiling tube in hot water and boil for 10 minutes or until the leaf

decolourizes. ( It may be necessary to replace the ethanol)7. Gently remove the leaf and wash with a fine trickle of cold tap water.8. Spread the leaf evenly on a white tile.9. Add a few drops of iodine/potassium iodide solution to the leaf and note any

observations

Record:

Observation Appearance of leaves before testing for the presence of starch

Appearance of leaves after testing for the presence of starch

Plant

The leaf was flaccid (soft) after being boiled in water The ethanol changed from colorless to green The leaf was brittle after being boiled in ethanol The leaf become flaccid once more after being rinsed in cold water After iodine solution was added:

Observation Interpretation

No color change (Iodine Solution remains brown)

Iodine changed from brown to blue- black

Conclusion:

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