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Investigating The Effect Of Light Intensity On Cress Seedlings.

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Investigating The Effect Of Light Intensity On Cress Seedlings Aim - To investigate whether or not light intensity affects the growth of cress seedlings. Hypothesis - I predict, the higher the light intensity, the more the cress seedlings will grow. Theory - The theory of photosynthesis states that a plant needs 4 things to photosynthesise and make food (glucose) for itself; these are light, chlorophyll, carbon dioxide and water. In addition, 3 factors affect the rate of photosynthesis; they are light intensity, carbon dioxide and temperature (as I am testing light intensity, carbon dioxide and temperature will be ket as controls to ensure a fair test). If the light intensity is low, the rate of photosynthesis, and growth of the seedlings, will slow down as well. This is because the chlorophyll in the cress can only photosynthesise and grow as fast as the light energy is arriving. ...read more.


and the size of the holes. Apparatus - * 6 Petri Dishes * Cotton Wool * Black Card * Hole Puncher * Cress Seeds * Sellotape Method - 1. I will cut 6 circles of card the same area of the surface area of the petri dishes and punch holes into them to alter light intensity; the number of holes will be 1, 3, 5, 7, 9 and 11. 2. I will then stick these onto the petri dish lids. 3. After that, I will flatten out the wool to 1cm in thickness and cut out 6 5cmx5cm squares, dampen them, and then put them into the petri dishes. 4. Fourthly, I will put 6 seeds into each dish, evenly spread out, and put the lids, with the pieces of card on them, back on. 5. Then I will put them onto a windowsill. ...read more.


I observed there was only a 0.08cm difference in height between the cress seedlings averages in the petri dishes with 3 and 5 holes. This is because, a seed already has a food store, and if the shoot cannot find sunlight it uses the food store it already has, to grow in search of sunlight. The result for the petri dish with 3 holes was the only anomalous result, all the rest were correct because I successfully blocked out any extra sunlight other than the light coming through the holes. Evaluation - If I were to do the experiment again I would find a better way to vary light intensity and I would like to be able to somehow measure the light intensity and put it into a graph in relation to the growth of the seedlings, to see if there are any other patterns to be observed. After doing this experiment I would like to test the affect of limited carbon dioxide and varying temperature on cress seedlings. ...read more.

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