Small Splashes in Photosynthesis: 7 Idiots and a Colorimeter

March 15, 2013

  • Hello again people of the inter webs I am departing from the videos for a sec simply because I need to prep my self for the AP Biology exam so I will be writing post to do so.

Get ready for some gigantic posts coming your way because I have three topics that I will be discussing and each is getting a rather large chunk of my thought and time.

We are going to start with Photosynthesis. What is photosynthesis? well simple answer is the process by which plants convert light Water (H2O) and Carbon dioxide (CO2) Into oxygen and Sugar for storage and consumption. And the complicated version is the rest of this post.

First experiment:

Plant Pigment Gradient

The first in our series of experiments on photosynthesis was a 15 minute mini lab that’s purpose was to help us understand the coloring of the of leaves that perform photosynthesis and the different pigments within the leaves that serve different functions at different points during the year

  • ›Step 1 Procure some leafy greens(Spinach)
  • ›Step 2 get some filter paper
  • ›Step 3 Cut the paper in to a strip with point, using the edge of a coin press the spinach leave into the filter paper ¼ of the way up from the tip, this should leave a green line on the paper.
  • ›Step 4 pour some diffusion solution into a plugable container but not too much
  • ›Step 5 Dip only the tip of the paper into the solution and leave it up right in the container, then plug the container
  • ›Step 6 Profit.

If done correctly the result after about 10-15 minutes should be this.

Evernote Camera Roll 20130207 011124

The purpose of this Experiment was to expose the below pigments.

Evernote Camera Roll 20130207 011102

You all know what chlorophyll is but whats Carotene, well carotene is just like it except during the fall when the chlorophyll is no longer needed because of the decrease in photosynthesis it shuts down and all that’s left is the Carotene, that is why leaves change colors during the fall.

Now lets discuss the Actual process of photosynthesis. It starts in side the Chloroplast. Inside the chloroplast light strikes the different pigments we discussed earlier and inside the pigments there are small amounts of metal (magnesium). This causes Electrons to fly off of the pigments and Create ATP when it passes through proteins, starting the photosynthesis process. All of the actions take place inside the granum which is and oval like structure with many of the same structure stacked on top of each other, this is inside the Chloroplast inside the plant cell. In the granum there are 2 major reactions that take place. The Light Dependant, and the Light Independent.

The Light Dependant Reaction starts with the electrons freed from the Chlorophyll and that electron generates ATP and NADPH2. This energy is then passed on to start the Independent reaction.

The Light Independent reaction starts when the ATP and NADPH2 start to react with carbon. A 5 carbon chain meets up with another carbon and becomes a 6 carbon chain this is then split by ATP and NADPH2 into two 3 Carbon chains, these chains have picked up some hydrogen molecules and that makes them glycerol which can then be made by their process into sugars and all other kinds of things necessary for the function of the plant. The hydrogen that latched onto the carbon chain actually came from water and that oxygen leaves the plant through chemi-osmosis henceforth giving us the oxygen in our atmosphere.

Now that you know the basics of the actual process let’s get into the other more hefty experiments we did.

Using a colorimeter which is a device that measures how much light is absorbed by that ever is in tha path of the beam of light that runs through the device. We constructed two separate experiments. Using hole punched circles from spinach leaves we tried to measure the productivity of photosynthesis in different colors of lights. In the first experiment we used BTB solution which starts blue, then reacts with CO2 to turn orange. We reacted the BTB with CO2 by blowing into it the solution turned orange and we put the spinach circles into the solution measured it then set it to be under the light for 15 minutes then measured again after words to find the percent of change we were hoping to view  the use of CO2 in the solution for photosynthesis by the solution turning back to blue. the results of that experiment are as follows in percent of change

White 150% change in absorbance

Red 423%

Green 263%

Black light 442%

Now The results we found interesting; Being that plants are green meaning that they reflect green light  so the fact that the Change was so high in our green Light but not in our white light which is all of the colors of light was slightly shocking.  How ever the red light and black light are easier to explain. Chlorophyll Absorbs a lot of red light so the fact that the rate was high is expected. The black light is Ultraviolet light so it has and even higher absorption rate than Red lights because it’s on the tail end of the visible light spectrum.

USing the same basic idea of the last experiment we thought about another way to measure whether photosynthesis is occurring which is through the amounts of electrons that are released. As I covered earlier electrons are released during photosynthesis to create energy. Our second solution was one of water and DPIP. This solution starts dark blue and progressively gets lighter colored the more electrons travel through it. For this experiment we also set up a control testing weather or not the lights would lighten the solution on their own, and another with spinach circles in it but covered in tin foil so that the light  could not start the photosynthesis reaction. here are our results.

note- the light control confirmed that light did not change the DPIP solution at all.

White :30.78%

Red :28.53%

Green :6.75%

Black :-1.53%

Foil Control:-3.03%

As you can tell when we rethought our experiment it was a major improvement the data is more conclusive and more consistent with what we know about photosynthesis and the experiment its self was more controlled and efficient. The negative values you see are were cause by the DPIP solution get darker. this is only possible because to begin with those solution were measure before the experiment and the had been exposed to light be for hand. During the actual experiment all of the light were of except for the spotlights trained on the subjects.

In conclusion, based on our studies and final experiment on photosynthesis We can deduce that photosynthesis occurs best in white or red lights. Until next lab “bows” Farewell.


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