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Name:____________________________________
Class:_____________________
Topic: Photosynthesis Lab Report: Testing a Leaf for the Presence of Starch Date: 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 S unlight is the source of energy. Chlorophyll is foun d 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: Sunlight Carbon dioxide + Water
Sugar + 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
Plant
Appearance of leaves before testing for the presence of starch
Appearance of leaves after testing for the presence of starch
• • • • •
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 e thanol 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: _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _____