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Comparing the growth of pea plants grown in the light and in the dark

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Biology Coursework by Duncan Garnett Experiment 1 - Comparing the growth of pea plants grown in the light and in the dark Aim: To compare the vertical growth and weight gain of pea plants grown in the light and in the dark. Background Knowledge: Photosynthesis forms the basis for this experiment. This is the process by which a plant makes food for itself from the raw materials around it. The energy needed for photosynthesis comes from sunlight, which is the variable for this experiment. The substance that absorbs sunlight is chlorophyll, which is mainly contained in chloroplasts. This energy is used to convert carbon dioxide (CO2) and water into sugars. This conversion creates the waste product oxygen, which is used by humans for breathing. Without being able to photosynthesise plants will stop growing and die. In a plant growing in the dark the chlorophyll will slowly be destroyed causing them to use their food reserves. Once the reserves have been used the plant will die. This is what happens in plants that are not grown in sunlight. Etiolation is a phenomenon that occurs in plants not being grown in sunlight, whereby the stem of the plant rapidly elongates to increase the probability of the plant finding light. ...read more.


* After 3 weeks of growing each plant was removed from the pot and the soil was cleared from the roots. The roots were then washed and the plants were put into envelopes for a week to dry. * Once completely dried the plants were removed from their envelopes and weighed, with their weights being recorded in a table. Results: Plant Heights in Centimetres (cm) 19 / 6 / 02 26 / 6 / 02 3 / 7 / 02 Increase from 19 / 6 / 02 Light - Pot 1 18.0 24.5 25.2 7.2 Pot 2 16.0 25.9 26.5 10.5 Pot 3 12.0 32.4 25.4 13.4 Pot 4 12.1 16.0 16.7 4.6 Pot 5 13.1 20.1 18.2 5.1 Pot 6 8.0 9.0 9.5 1.5 Total 79.2 127.9 121.5 42.3 Mean 13.2 21.3 20.3 7.1 Dark - Pot 7 18.0 18.2 16.5 -1.5 Pot 8 17.8 19.0 13.5 -4.3 Pot 9 - - - - Pot 10 17.0 17.0 17.4 0.4 Pot 11 12.3 13.0 11.1 -1.2 Pot 12 - - - - Total 65.1 67.2 58.5 -6.6 Mean 16.3 16.8 14.6 -1.7 Dry Weight of Plants in grams (g) ...read more.


Pot 5 also showed a slight decrease in height over the 3rd week of the experiment but this is more likely caused by leaf drop-off or growth beneath the surface of the soil rather than above. In terms of weight, pot 11, which was the shortest of the surviving plants in the dark was the heaviest of those grown in the dark, but this may well be due to extensive root growth rather than growth of stems and leaves. The main improvement I would make to this experiment would be to increase the amount of results obtained in the experiment, in order to draw more accurate averages and more concrete conclusions. This would include using more plants in both the light and the dark, recording growth everyday to compare the point at which plants in the light grow faster and also I would lengthen the experiment to compare the flowering and pea production of plants under different light conditions. Another improvement would be to compare growth under different light intensities, in order to determine the ideal intensity of light in which to grow plants. However this would require further equipment and more controlled environments to implement and is not possible on the available scale. ...read more.

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