Testing+Leaves+for+starch

Section 2- Structures and functions in living organisms a) Levels of organisation - b) Cell structure - c) Biological molecules - d) Movement of substances - e) Human Nutrition - e) Plant Nutrition - f) Respiration - g) Gas exchange (Humans) - g) Gas exchange (Plants) - h) Transport (Humans) - h) Transport (Plants) - i) Excretion - j) Coordination and response

This practical is in two parts:
 * Setup a variegated plant to photosynthesize
 * Test the leaves for starch and analyse your findings

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 * Setup a variegated (leaves coloured both green and white) plant**
 * 1) De-starch the plant by keeping the plant in darkness for 48 hours prior to the lab (this should have been done for you)
 * 2) Cover both part of the green region and part of the white region of one leaf
 * 3) Put the plant in a well lit location for 1-2 days

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 * Testing the leaf for starch**
 * 1) Cut off the leaf you partially covered.
 * 2) Use the whole leaf if it is small if not make sure the section of leaf you use includes: a green covered section, a green uncovered section, a white covered section and a white uncovered section.
 * 3) Pour some boiling water from a kettle into a large beaker. (alternatively water can be boiled using a bunsen burner)
 * 4) Place the leaf in the hot water for about two minutes
 * 1) Using forceps, remove the leaf from the boiling water. Note how it has changed.
 * 2) Drop the leaf into a test tube and push it to the bottom
 * 3) Add enough ethanol to cover the leaf, and stand the test tube in your beaker of hot water. (BUNSEN MUST BE TURNED OFF)
 * 1) Wait a few minutes, watch as the ethanol boils and the green colouring (chlorophyll) is removed from the leaf.
 * 2) Using forceps, remove the leaf from the boiling tube and rinse the leaf in cold water. //Be careful when removing the leaf as it will be very brittle until you rinse it.//
 * 1) Put the leaf on a white tile and cover with iodine solution.
 * 1) Wait a few minutes and watch for colour changes. Does any part of the leaf become blue-black?

Safety considerations
 * Use eye protection
 * Be careful of the hot liquids
 * Wash your hands to remove any traces of plant sap, or the chemicals that you have used.

Image of a variegated leaf tested for starch

Analysis of the results
 * 1) What was the role of the boiling water?
 * 2) What was the reason for soaking the leaf in ethanol?
 * 3) Which regions of the leaf did not produce starch, give reasons why?
 * 4) Which regions of the leaf did produce starch?
 * 5) The lab proves that two things are needed for photosynthesis to occur, what are they?
 * 6) Photosynthesis produces glucose, why do we test for starch not glucose?

Images courtesy of [|Practical Biology]