The loopy leaf6/1/2023 ![]() Once it is demonstrated that all starch has been utilized or removed, photosynthesis is allowed to take place by exposing the plant to sunlight. To improve this experiment, the plant needs to be de-starched, and the leaves tested for the presence of starch. How can this experiment be extended to demonstrate conclusively that photosynthesis has taken place? We do not know whether starch has accumulated in the leaf as a result of photosynthesis or whether the starch is permanently present in the leaf. Do your results indicate that starch is the first product of photosynthesis? The results do not indicate whether starch is the initial, intermediate or final product of photosynthesis. Which products of photosynthesis may be present but not revelead by the iodine test? Glucose, fructose and sucrose are all carbohydrate products of photosynthesis not revealed by the iodine test for starch. Iodine solution is an aqueous solution of iodine/potassium iodie – potassium tri-iodide water is needed inside the leaf to enable penetration by diffusion. The leaf was rinsed in water to rehydrate it. The leaf was brittle as ethanol dehydrated (extracted water) from the leaf.Įxplain the significance of rinsing the leaf in water. Account for the texture of the leaf after being boiled in ethanol. Ethanol is an organic solvent and so extracts chlorophyll from the leaf. A decolourized leaf is pale yellow or green. theleaf needs to be ‘ decolourized’ for chabges to be observed. ![]() Chlorophyll needs to be removed from the leaf i. The leaf was flaccid (soft) as cell membranes were ruptured and turgor pressure was lost.Įxplain the significance of boiling the leaf in ethanol Chlorophyll is a green pigement and so masks the colour change of the iodine test for starch. Boiling arrests all chemical reactions, since enzymes which catalyse the reactions are denatured.ĭenatured enzymes have altered or destroyed active sites due to heat, pH, ionic concentration Account for the texture of the leaf after being boiled in water. Denatures enzymes, particularly those which convert starch to glucose e.Cell membranes are selectively permeable and do not readily allow the penetration of iodine. Ruptures cell membranes to make starch granules in cytoplasm and chloroplasts accessible to iodine/potassium iodide solutiion.Removes the waxy cuticle which prevents entry of iodine/potassium iodide solution.Explain the significance of boiling the leaf in water.The iodine solution will turn from brown to blue – black. Which organic substance does iodine/potassium iodide solution detect the presence of? What observations will you make if the test is positive? Starch. Glucoe may be immediately used, translocated in the form of fructose or sucrose or stored as starch granules. The carbohydrate, glucose is first formed. In the light – independent stage enzymes catalyse the reduction of carbon dioxide by hydrogen. Hydrogen enters the second stage, oxgen is gaseous by-product. In the light-depedent stage, water is photolyzed by sunlight into Hydrogen and oxgen. Photosynthesis involves 2 stages – the Light-dependent Stage and the Light-independent stage. Most photosynthesis takes places in the green parts of plants, in particular the leaves. Photosynthesis is the process by which light energy is harvested by chlorophyll and used to convert inorganic raw materials – carbon dioxide and water to the products glucose and oxygen. The leaf become flaccid once more after being rinsed in cold waterĭescribe Photosynthesis.The leaf was brittle after being boiled in ethanol.The ethanol changed from colourless to green.The leaf was flaccid (soft) after being boiled in water.Add a few frops of iodne/potassium iodide solution to the leaf and note any observations.Gently remove the leaf and wash with a fine trickle of cold tap water.( It may be necessary to replace the ethanol) Place the boiling tube in hot water and boil for 10 minutes or until the leaf decolourizes.Place the boiled leaf in a boiling tube containing 90% ethanol.(If you are using a heat source without a naked flame – electric water bath or hot plate – this step is uneccesary. Use the forceps to place the leaf in the boiling water.Remove a green leaf fom a plant that has been exposed to sunlight for a few hours.The Procedure outlined below is slightly different. The video above shows the steps in Testing a Leaf for the Presence of Starch.leaf to be tested (hibiscus leaves are excellent).bunsen burner, tripod stand, wire gauze(OR 90oC electric water bath OR hot plate).Biology Photosynthesis Lab APPARATUS/MATERIALS
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