Manipulation Of Photosynthesis

Manipulation of Photosynthesis

Abstract

These experiments in this study was to show how significant it is for plants to receive all

its inputs, so it can produce all its outputs in photosynthesis. Our initial hypothesis was correct

for all three experiments, because we predicted that the change in light and carbon dioxide would

affect how much starch the plant produced. We also predicted that the baking soda would speed

up the process of photosynthesis, which caused it to produce more oxygen. This helped us to

conclude that sunlight, carbon dioxide and water are all necessary for photosynthesis to occur

and to be successful.

Introduction

Plants are the foundation for many ecosystems and for humans as a whole. Agriculture in

South Dakota alone leads the state in revenue and at the end of the day it all comes back to

plants. Starch in plants positively affects agricultural yield of a number of crops (Stark). Plants

produce starch (carbohydrates), oxygen and water through the process of photosynthesis. To start

this process though, plants need sunlight, carbon dioxide and water (Mader). In this lab we

manipulated the inputs of photosynthesis to see how it affected its outputs. We also tried to speed

up photosynthesis using baking soda with a water plant. Even though marine plants rate of

photosynthesis is very similar to that of terrestrial plants, we found a way to make it faster

(Black). In both cases, we got to see what photosynthesis makes and how changing the inputs of

it will change the outputs.

Materials and methods

We first started off by doing a little experiment to test for starch. We started off by

placing a couple drops of starch, glucose, and distilled water in three different depressions of the

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spot plate. After this we placed a drop of iodine solution into each spot. We then recorded our

observations.

Our next experiment started off by collecting three leaf samples from the greenhouse.

Each leaf simulated different situations. One plant was in the dark room, another one was in a

closed environment, and the third was left in the light but had a section of the leaf covered up.

After the leaves were recovered, two beakers were filled. One was filled with water and one

filled with alcohol. The amount of liquid put into either beaker does not matter, but we filled

both half full. Both beakers were then brought to a boil. Once both were boiling, we placed one

of the leaves into the boiling water for about a minute. Then we pulled it out with forceps and

placed it into the boiling alcohol until the color pigments had been extracted. The leaf was then

taken out of the boiling alcohol and dipped into the boiling water to soften it back up.

Once the leaves were taken out of the boiling solutions, they were placed in a petri dish

and then soaked in an iodine solution. After letting the leaf soak for a couple minutes, we then

rinsed it off and floated it in water. We then observed the patter of staining. This was done with

all three leaves.

Our second experiment was to test the effect of an external carbon source on

photosynthesis. First, we filled up two separate beakers half full with water. We set one beaker

aside and put two teaspoons of baking soda into the one beaker and labeled it. We then added

equal amounts of Elodea into each beaker. After this, both beakers were covered with plastic

wrap and set underneath a lamp for fifteen minutes. After the fifteen minutes we observed what

we saw and wrote it down. Next, we covered both beakers completely with aluminon foil. Again,

we let it sit for fifteen minutes and recorded your observations after.

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Results

The first experiment results were that only one of the solutions turned a

dark purple. The other two solutions did not change at all as you can see in

Figure 1.

Our results during the next experiment was what we expected. The leaves

showed what we expected they would show. The leaf that was left in the light

and had the part covered up showed the most purple color where the leaf was not

covered up. The part where the leaf was covered showed little to no purple color

which was expected (Figure 2). The leaf that was left in the dark showed almost

no purple at all which was also expected (Figure 3). The leaf that was left in a closed

environment had very little purple in it, only showing some towards the middle of the leaf

(Figure 4).

Lastly, our results for the external

carbon experiment was also expected. There appeared to be more gas produced in the beaker

with the baking soda. This was what we hypothesized. In the second part of the experiment

though, the one with baking soda had less bubbles (Figure 5).

Figure 1. The 3 solutions

tested for starch.

Figure 2. Leaf left in

light with left edge

covered. Figure 3. Leaf

that was left in

the dark.

Figure 4. Leaf left in a

closed environment.

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Discussion

Based on the colors in the very first experiment, we could easily tell which liquid was

starch because it turned purple right away. Iodine will turn starch purple, which helped us lead

into the experiment dealing with the leaves. As we know, photosynthesis produces

carbohydrates, which is a starch. Because it is a starch we could test for it in the leaves and again

look for the purple color. The leaf that was left in the light was our control so we could see what

a leaf should look like, but it had a part of it that was covered up and could not receive light.

Once, we died the leaf the section that was exposed to light turned purple but the part that was

not could not turn purple because it had no starch in it. It had no starch because it did not have

light which is needed in photosynthesis. Sunlight, carbon dioxide and water are all needed in

photosynthesis, so the part that was covered up could not properly do photosynthesis (Mader).

This was also true for the plant that was left in the dark. Because it had no sunlight, it could not

do photosynthesis so it appeared to have no purple color in it. Lastly was the plant that was in a

closed environment, which had another part to make photosynthesis was cut off. Instead of

having no light this time, the plant had no carbon dioxide so it again could not complete the

Figure 5. Baking soda beaker on

the left and regular water on right.

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process of photosynthesis. We could see this because again there was no purple in the leaf when

we stained it.

In the experiment with the baking soda, we also got to observe the process of

photosynthesis. When the beakers were just covered with plastic wrap, the plant with the baking

soda produced more bubbles which means more gas. It had more bubbles that were collecting

on the leaves because it is producing more oxygen. By adding NAHCO 3 the reagent is causing

photosynthesis to speed up which is not present in the other solution. After we covered the

beakers up though, the amount of bubbles in the baking soda slowed down and the one without

baking soda caught up. This again proved that the baking soda helped speed it up.

Overall, all three experiments helped to understand the process of photosynthesis.

Without having all three inputs of photosynthesis, it is unable to produce its outputs. This was a

good manipulation of it.

Literature Cited

Black, C. C., J. E. Burris, and R. G. Everson. ‘Influence of oxygen concentration on

photosynthesis in marine plants.’ Functional Plant Biology 3.1 (1976): 81-86.

Mader, Sylvia S. and Windelspecht, Michael. 2019. Photosynthesis. Biology, 13 th Edition. 113-

125.

Stark, David M., ‘Regulation of the amount of starch in plant tissues by ADP glucose

pyrophosphorylase.’ Science 258.5080 (1992): 287-292.