1. Metabolic Pathways of Plants Nathan J. Smith Undergraduate in WFS Tennessee Technological University Cookeville, TN 38501

2. Introduction  Objective: The object of this experiment was to show how a plant (coleus) grown in the dark for up to two weeks will not photosynthesize and therefore convert its starch back to glucose in order to perform cellular respiration.  Hypothesis: The plants grown in sunlight will photosynthesize and produce starch which will be stored. The plants grown in darkness will utilize their starch for cellular respiration. Once the plant uses all its starch, it should die.  Null Hypothesis: Both plants will photosynthesize, store their starch, and grow to maturity.

3. Introduction  Starch is a major storage component in plants which strongly affects how well the plant will mature. (Stark 1992)  The synthesis of starch from photo-assimilated carbon is one of the major biochemical fluxes in plants. (Zeeman 2004)  Soluble sugars like sucrose and glucose play a very important role in plant structure and metabolism. (Ivan 2006)  Plants receive energy from the sun through a chemical process called photosynthesis, which also produces oxygen in its breathable form. (Webber 2005)

4. Introduction  In Whitehead’s study on the response of total night-time respiration in plants, he and his group of scientists found that respiration is dependent on total photosynthesis during the previous day and that the response is mediated through changes in storage in carbohydrate pools. (Whitehead et al. 2004)

5. Methods and Materials  I placed two groups of coleus plants in two different environments. Group A was exposed to sunlight and group B was exposed to darkness/shade only.  After two weeks, I removed one leaf from each plant kept in the dark and one leaf form each plant which was exposed to light.  I placed the leaves in a beaker full of about 150 cc’s of water and placed it on a hotplate until it began to boil.  Once the leaves had been in the boiling water for about two minutes, I took them out and placed them into another beaker which contained about 75 cc’s of ethanol.

6. Methods and Materials  Once the ethanol began to boil I waited till the leaves lost all their pigment(s) and then removed them from the boiling ethanol.  I kept group A separate from group B by tying a tea-bag string around the stems of the leaves which were kept in total darkness (group B).  After flattening the leaves on a watch glass I placed two to three drops of iodine solution on each leaf, which would then let me know how much starch was present. (Whitehead 2004)

7. Results  The plants from group A, which were grown in the light, promoted more starch than plants from group B, which were placed in the dark/shade.

8. Results Promotes high amount of starch Promotes little starch Promotes no starch at all Group A ☼ ☼ ☼ Group AA ☼ ☼ ☼ Group B ☼ Group BB ☼

9. Results  The two plants from group A ended up having over twice the amount of starch present after both experiments were over.  Although group B were almost dead, they still had a small amount of starch left.

10. Results % of Starch in Leaves 0% 5% 20% 40% 60 % 80% Group A Group AA Group B Group BB

11. Discussion  All plants must photosynthesize if they have any chance of growing during their life cycle. Their food is a substance known as starch. (Stark 1992)  After my experiment was over, the plants left in complete darkness for two weeks had a very small amount of starch present. The reason for this is that the plants used up all their food (starch) in order to survive. Placing a plant in the dark is like placing a human on a desert island with a few bananas and some water. He will survive as long as he utilizes his food, but once he runs out he will die just as the plant will. Soluble sugars like sucrose and glucose also play a very important role in plant structure and metabolism. (Ivan 2006)  Before the plants in group B began to die they converted what glucose they had left back into starch, which would allow them a few extra days of survival. However, once all glucose was converted and all the starch was gone…the plants began to wilt away.

12. Discussion  The plants which were exposed to sunlight for two weeks had a much higher amount of starch present after the experiment. This is because they were able to turn energy from sunlight into bio-energy through a chemical process called photosynthesis, which also produces oxygen in its breathable form. (Webber 2005)  In order to achieve this, a plant must have carbon dioxide, water, light, and photosynthetic pigments. (Ensminger 2006)  Placing the coleus plants in shade for two weeks did not affect sugar concentrations but reduced starch concentrations in the leaves, leading to lower rates of respiration at night. (Whitehead et al. 2004)

13. Conclusions  The hypothesis was accepted.  The plants left in the dark for two weeks were almost wilted due to a loss of starch.  The plants which were exposed to light for two weeks did great and were full of starch.  The experiment was a success and should prove why it is important for plants to receive the proper amount of sunlight.

14. Literature Cited Couee, I., Sulmon, C., Gouesbet, G., Amrani, A. 2006. Involvement of soluble sugars in reactive oxygen species balance and responses to oxidative stress in plants. Journal of Experimental Botany. 57:449-460. *  Ensminger, I., Florian, B., Norman, P., Huner, A. 2006. Photostasis and cold acclimation: Sensing low temperature through photosynthesis. Physiologia Plantarum. 126:28- 36.  Kozlowski, T., Pallardy, S. 2002. Acclimation and adaptive responses of woody plants to  Environmental stresses. The Botanical Review. 69:270-336.  Stark, D., Barry, G., Preiss, J., Kishore, G., Prado. 1992. Regulations of the amount of starch in plant tissues by ADPGIc pyrophosphorylase. American Association for the Science. Science. 258:287-297.  Webber, K. 2005. Scientists Discover How Plants Disarm the Toxic Effects of Excessive  Sunlight. Ascribe Higher Education News Service.

15. THE END QUESTIONS??? QUESTIONS???