Transcript Final Power Point Presentation

Metabolic Pathways of Plants
Nathan J. Smith
Undergraduate in WFS
Tennessee Technological University
Cookeville, TN 38501
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.
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)
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)
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.
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)
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.
Results
Group A
Promotes
high
amount of
starch
☼☼☼
Group AA
☼☼☼
Promotes
little starch
Group B
☼
Group BB
☼
Promotes
no starch at
all
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.
Results
% of Starch in Leaves
80%
60%
40%
20%
5%
0%
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.
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)
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.
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. 126:2836.

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.
THE END
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