Testing a leaf for starch - Kerboodle

1 Student practical name .. class .. Date .. Oxford University Press 2016: This resource sheet may have been changed from the original. 1 Testing a leaf for starch Specification references Uses of glucose from photosynthesis WS WS WS AT 8 Aims You should be able to follow a method and understand the justification for the steps in that method. You should work safely and have an appreciation of the risk factors. Learning outcomes After completing this activity, you should be able to: use a given method to carry out the starch test on the leaf describe the ways plants makes use of glucose.

2 Background Biologists need to be able to test for a range of biological molecules. It is possible to test leaves for starch . If photosynthesis has occurred, sugar will be produced in leaves and converted to starch . Safety Ethanol (alcohol) is HIGHLY FLAMMABLE AND HARMFUL. Ensure that all naked flames are extinguished before using it. Container for waste ethanol NOT to be disposed of in sink Iodine will stain hands and clothing. Use of glassware. Wear eye protection. Equipment and materials tripod gauze Bunsen burner heatproof mat 250 cm beaker Student practical name .

3 class .. Date .. Oxford University Press 2016: This resource sheet may have been changed from the original. 2 boiling tube forceps glass rod ethanol eye protection white tile iodine solution Method 1 De- starch the leaves of the plant before the experiment by placing into a dark cupboard for 24 hours. 2 Set up the plant as shown below. 3 Boil 150 cm3 of water in a beaker or collect boiling water from a kettle. 4 Place the leaf to be tested in the water for 2 minutes: this kills the leaf, stopping further photosynthesis. Student practical name .

4 class .. Date .. Oxford University Press 2016: This resource sheet may have been changed from the original. 3 5 Remove the leaf from the water and place in a boiling tube. 6 TURN OFF THE BUNSEN BURNER. 7 Add ethanol to the boiling tube to cover the leaf. Your teacher may choose to handle the alcohol/ethanol here. 8 Place the boiling tube in the hot water for 10 15 minutes; the ethanol should boil and remove the chlorophyll from the leaf. Student practical name .. class .. Date .. Oxford University Press 2016: This resource sheet may have been changed from the original.

5 4 9 Now remove the leaf from the ethanol. 10 Dip the leaf into the hot water to soften the leaf (see diagram at point 4 above). 11 Spread the leaf out on a white tile. 12 Cover the leaf with iodine solution. 13 Areas that turn black contain starch , whereas areas of the leaf that stay brown do not contain starch . Results Draw a diagram of your leaf. Questions 1 name the zone of your leaf that produced starch . (1 mark) 2 name the process that produced the starch . (1 mark) 3 Some of the glucose produced in photosynthesis is converted to starch . a name three other products that glucose can be converted into in a plant.

6 (3 marks) b Explain why the plant stores glucose as starch . (2 marks) Student practical name .. class .. Date .. Oxford University Press 2016: This resource sheet may have been changed from the original. 5 4 Describe one step taken in the experiment as a safety precaution. (1 mark) 5 Explain why the plant needed to be de-starched prior to the experiment being set up. (2 marks) Student follow-up There are a number of complex steps in the method for Testing a leaf for starch . 1 Explain why each of the following steps are carried out: a boiling the leaf in water (1 mark) b boiling the leaf in ethanol.

7 (1 mark) 2 Explain why you can t simply add iodine to an untreated leaf to test for starch . (2 marks)