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The effects of how light intensity within storage of potatoes effect the rate of catalase activity will be investigated.

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Biology planning skills assignment Potatoes, like all other vegetables contain the enzyme catalase, which breaks down the toxic waste product of hydrogen peroxide. Potatoes have an unusual response to long exposures of light, where the chemical properties are altered within the cells. This can be seen as the surface changes green in colour. Storage conditions of potatoes are therefore important, to ensure potatoes remain in the original state after cultivation. Within this assessment, the effects of how light intensity within storage of potatoes effect the rate of catalase activity will be investigated, and a suitable experiment to obtain results showing this will be devised. Potatoes belong to a family of plants called the Solacaneae, which includes the tomato and eggplant. These species of plants naturally produce glycoalkaloids, a toxic substance to protect them from predators. Within potatoes, this glycoalkaloid is solanine, and is present within relatively high concentrations within the stem and leaves. However, within the tuber, solanine is low in concentration and can be found on the surface, about one eighth of an inch in depth. When exposed to light, the solanine concentration increases by about ten times. Simultaneously, the chlorophyll is produced, which changes the surface to green in colour. The formation of chlorophyll has no effect on the increase of solanine, however, the conditions which accumulate it, also increases the concentration of the glycoalkaloid. Thus, a green surface colour on a potato tuber is a clear indication of increased solanine levels. Solanine, like all glycoalkaloids are is a toxic substance to animal species. When consumed, they inhibit a group of enzymes called cholinesterases which are critical to the function of the nervous system. Within humans, this can cause severe vomiting and if the concentration of solanine is high enough, even death. Glycoalkaloids are as suggested by its name, alkaline in pH, and any potatoes with high concentrations of this substance is bitter in taste. All light affects the chemistry within potato cells; however, different types affect it in different ways. ...read more.


Four light intensities are needed to compare the rate of reaction for, to come a firm conclusion from the results. The first potato will be right next to the lamp, and therefore be fully exposed to the whole intensity. The other potatoes will follow this by being 30cm behind each other, so that the second potato will have half the intensity, the third will have a quarter the intensity, and the last an eighth. Comparison within ratios between the light intensity is enough to draw a strong conclusion from the results to be obtained. It is certain that low light intensity achieved by a longer distance from the florescent lamp, will cause less light induced solanine to be produced. This lower content will mean that the pH of the peroxisomes whence the catalase is present will be increased by only a little. With contact with 20 volume hydrogen peroxide concentration, the reaction will be quite fast. It is therefore ideal that a 20ml measuring cylinder be used to measure the dependent variable, the volume of oxygen produced, as this is large enough to measure the volume over the four minute period allowed. Variables The independent variable here is the light intensity upon which the same variety of King Edward potatoes will be exposed to. This will be done within a darkened room where only a fluorescent lamp will be a light source, and the potatoes will be exposed to different light sources due to their distance from it. To ensure that the potatoes are exposed to the same light intensity at all times, and that the chemical changes within the potato tissue is due to the same exposure, it is important that the fluorescent lamp maintains the same power throughout the time needed for the potatoes to turn green. This could be over three days, and therefore there is a likely chance that the fuse could go, or the lamp could get overheated. ...read more.


Using the 12mm potato cutter, chop potato tubes from one of the potatoes. Cut 12 5mm thick potato disks ensuring they are cut next to the edge. Put them in a labelled Petri dish. Do the same for the other three potatoes. 2. Fill the water bath to half full. Fill the measuring cylinder with water. Place upside down into the water bath so that no air is let in. Clamp this into position. 3. Position the conical flask with the wooden blocks, and ensure that the end of the glass tubing enters the measuring cylinder. 4. Put four disks of the first light intensity within the conical flask. Pour some of the hydrogen peroxide solution within a beaker. Using a pipette transfer 20ml of the solution to a labelled beaker. 5. Pour the hydrogen peroxide solution into the conical flask. Put the rubber bung on and start the stop clock immediately. 6. Add the vaseline to the rubber bung 7. Record the volume of oxygen collected within the measuring cylinder at every minute for four minutes. 8. After four minutes, remove the conical flask. Empty the contents, and wash out the flask and bung using tap water. Then wash out using distilled water. 9. Repeat steps 2-8 for to obtain all the results for the repeats and the other potato disks of different intensities. Ensure you repeat each light intensity potato disk experiment twice to obtain three sets of results for each one. Hypothesis When exposed to light, the solanine concentration on the surface of the skin will increase. The light will also accumulate the formation of chlorophyll. The increased solanine, like any other glycoalkaloid will cause the cells to become alkaline. This will cause the peroxisomes where the catalase is stored to also become a high pH. Catalase, whose optimum pH is around 7.6, will slow down the rate at which it decomposes the hydrogen peroxide due to this change in high pH. Those potatoes closer to the fluorescent lamp will experience a higher light intensity. This will cause more chlorophyll and solanine formation faster than those potatoes further away. ...read more.

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