Understanding Photosynthesis: Energy Transformations and Chlorophyll Absorption

Exercise #6
PHOTOSYNTHESIS
In the process of 
photosynthesis
photosynthesis
, several energy transformations
take place.
 
-Light energy is captured by plant cells and is converted into
 
electrical energy in the form of high energy electrons.
 
-The kinetic energy of the electron is transformed into 
 
chemical energy in the bonds of ATP.
 
-The ATP, in turn, transfers the energy to the chemical bonds
 
of a glucose molecule.
Through this process, light energy from the sun is captured and 
stored in the chemical bonds of sugar molecules.
Exercise #6
PHOTOSYNTHESIS
 
PHOTOSYNTHETIC PIGMENTS
PHOTOSYNTHETIC PIGMENTS
The initial step of photosynthesis involves the capture of light
energy by the photosynthetic pigment, 
chlorophyll
chlorophyll
.
However, the plant does not absorb all of the light energy in
the visible portion of the 
electromagnet
electromagnet
ic 
spectrum
spectrum
.
 
-
Figure 6.1 of your lab manual represents the visible
 
portion of the electromagnetic spectrum.
In this exercise, you will use the spectrophotometer to determine
which wavelengths of light are absorbed and which ones are 
reflected by the chlorophyll molecule.
Exercise #6
PHOTOSYNTHESIS
 
PROCEDURE
PROCEDURE
In order to study the absorbance of various wavelengths of light
by chlorophyll, you must first separate the pigment from the leaf tissue.
This is accomplished by following the procedure below:
 
1)  Place a large spinach leaf into a 50 ml beaker and add 30 ml of ethanol.
 
2)  Place the beaker with ethanol on a hot plate and slowly heat the solution taking care not to crush the 
 
      leaf or boil the ethanol solution.
 
3)  As the chlorophyll exits the leaf tissue it will enter the ethanol solution and turn the color green.
 
4)  Fill the cuvette approximately 2/3 full will the chlorophyll extract.
Refer to the diagrams on the 
right for a representation of the
chlorophyll extract.
Exercise #6
PHOTOSYNTHESIS
At this point, we wish to determine which wavelengths of light
are absorbed by the chlorophyll extract.  However, we must first
ensure that the concentration of chlorophyll in the solution is 
appropriate for the experiment.
To do this, follow the procedure below:
 
1)  Set the spectrophotometer at 550 nm and depress the %T button.
 
2)  Place a cuvette filled 2/3 full of ethanol into the sample compartment and calibrate to 100 %T.
 
3)  In order to continue on with the absorption experiment you must obtain a reading between 65% - 85%.
  
-If you have a reading below 65%, your experimental solution is too concentrated--what 
  
should you do to change its concentration.
Once you have reached an appropriate %T reading you are ready to
continue with the experiment.
Exercise #6
PHOTOSYNTHESIS
Use your chlorophyll extract along with an ethanol blank and
determine the absorbance of the chlorophyll solution at various
wavelengths.
 
NOTE: 
the procedure employed here is identical to that used in the determination of the 
  
absorption spectrum for methylene blue (Exercise #3)
   
-remember to zero the machine after you change each wavelength.
In order to clearly visualize the actual absorbance characteristics
of your chlorophyll extract, you will plot your data using graphic
analysis.
 
Remember that wavelength is the 
independent variable
independent variable
 and
 
that absorbance is the 
dependent variable
dependent variable
.  Indicate with 
 
arrows on the x-axis the wavelengths of light most strongly
 
absorbed by the chlorophyll extract.
Exercise #6
PHOTOSYNTHESIS
 
LIGHT INTENSITY AND PHOTOSYNTHESIS
LIGHT INTENSITY AND PHOTOSYNTHESIS
In general, as the intensity of light increases, the rate of
photosynthesis increases.
 How does one measure the rate of photosynthesis?
 
As you should recall, oxygen is a by-product of photosynthesis.
 
Therefore, the photosynthetic rate can be determined by 
 
measuring the rate of oxygen production by the plant.
During this portion of the laboratory you will observe the effect
of light intensity on oxygen production and then make a generalization
on plant survival based upon the data you have collected.
Exercise #6
PHOTOSYNTHESIS
PROCEDURE
PROCEDURE
To determine the effect of light intensity upon photosynthetic rate, 
you will conduct the following experiment:
1)  Obtain a piece of 
Elodea
 5 to 6 inches in length and place it in a test tube with the cut end up.
2)  Fill the test tube with NaHCO3 (serves as a source of CO2) and plug with the rubber stopper containing
     the bent glass
 pipette
 an a 
syringe
.---AVOID AIR BUBBLES!
3)  The position of the fluid in the pipette can be adjusted by raising or lowering the plunger in the syringe
4)  Prepare a second tube filled with NaHCO3 without 
Elodea
 to act as a control for temperature and 
     pressure fluctuations.
5)  Place both tubes in a beaker filled with 
room temperature water.
6)  Place a lamp 75 cm from the experimental beaker and set up a heat filter (additional beaker) filled
     with tap water placed half way between the light source and the experimental beaker.
Refer to the picture on the following slide for reference.
 
Exercise #6
PHOTOSYNTHESIS
 
The following movie represents the experimental setup for the
light intensity experiment.
Exercise #6
PHOTOSYNTHESIS
 
PROCEDURE (continued)
PROCEDURE (continued)
75 cm - 
Move the lamp so it is 75 cm away from the experimental tubes and place the heat
 
 
  filter half way between the lamp and tubes.  
Wait 5 minutes for equilibration
.  Adjust
 
  the fluids in the pipettes so that they are at the 0.2 ml mark and recalibrate only when
 
  changing the distance to the light source.  Record the position of the fluid in the 
 
  pipettes at 2 minute intervals for 10 minutes.
50 cm - 
Move the lamp forward so it is 50 cm away from the experimental tubes and again place
 
  the heat filter half way between the lamp and experimental tubes.  Wait 5 minutes for 
 
  equilibration and adjust the fluid in the pipettes to 0.2 ml.  Repeat the experiment and 
 
  record your data in table 6.4.
 
25 cm - 
Repeat the equilibration, adjustments and measurements at the 25 cm mark.  Record 
 
  your data in Table 6.4.
 
Exercise #6
PHOTOSYNTHESIS
The changes observed in the tube containing 
Elodea
 are the
result of two simultaneous happenings:
 
1)  the production of oxygen by 
Elodea
 which will always
 
      result in an increase in volume, and
 
2)  fluctuations in temperature and pressure, which is why
 
      the pipette is set at the 0.2 ml mark.
To obtain a true reading of oxygen production, you must
To obtain a true reading of oxygen production, you must
subtract the control reading from the 
subtract the control reading from the 
Elodea
Elodea
 reading.
 reading.
Exercise #6
PHOTOSYNTHESIS
 
Graphic Analysis
Graphic Analysis
Plot all three cumulative movements of fluid as a function of time
on a sheet of graph paper.
It is suggested that different plotting symbols be used for each
distance from the light source (e.g. * for 75 cm; + for 50 cm; and 
- for 25 cm).
Using a clear plastic ruler, draw a straight line that best fits all 
points for each distance.  Your lines should indicate that 
the greater
the greater
the light intensity, the greater the rate of oxygen production 
the light intensity, the greater the rate of oxygen production 
by the plant
by the plant
.
Exercise #6
PHOTOSYNTHESIS
 
CONCLUSIONS
CONCLUSIONS
1)  You have seen that plants contain photosynthetic pigments.
1)  You have seen that plants contain photosynthetic pigments.
2)  Such pigments (chlorophyll) absorb only specific 
2)  Such pigments (chlorophyll) absorb only specific 
     wavelengths of light.
     wavelengths of light.
3)  The amount of light that the plant is exposed to has an
3)  The amount of light that the plant is exposed to has an
     influence on photosynthetic rate.
     influence on photosynthetic rate.
 
This powerpoint was kindly donated to
www.worldofteaching.com
 
 
 
 
http://www.worldofteaching.com
 is home to over a
thousand powerpoints submitted by teachers. This is a
completely free site and requires no registration. Please
visit and I hope it will help in your teaching.
Slide Note
Embed
Share

In the process of photosynthesis, light energy is converted into chemical energy stored in sugar molecules through multiple energy transformations. Chlorophyll plays a key role in capturing light energy. By separating chlorophyll from leaf tissue and analyzing its absorbance at various wavelengths using a spectrophotometer, we can determine the wavelengths of light absorbed by the chlorophyll extract. This experiment helps in understanding the absorption spectrum of chlorophyll and how plants utilize light energy for photosynthesis.


Uploaded on Sep 07, 2024 | 0 Views


Download Presentation

Please find below an Image/Link to download the presentation.

The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author. Download presentation by click this link. If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.

E N D

Presentation Transcript


  1. Exercise #6 PHOTOSYNTHESIS In the process of photosynthesis, several energy transformations take place. -Light energy is captured by plant cells and is converted into electrical energy in the form of high energy electrons. -The kinetic energy of the electron is transformed into chemical energy in the bonds of ATP. -The ATP, in turn, transfers the energy to the chemical bonds of a glucose molecule. Through this process, light energy from the sun is captured and stored in the chemical bonds of sugar molecules.

  2. Exercise #6 PHOTOSYNTHESIS PHOTOSYNTHETIC PIGMENTS The initial step of photosynthesis involves the capture of light energy by the photosynthetic pigment, chlorophyll. However, the plant does not absorb all of the light energy in the visible portion of the electromagnetic spectrum. -Figure 6.1 of your lab manual represents the visible portion of the electromagnetic spectrum. In this exercise, you will use the spectrophotometer to determine which wavelengths of light are absorbed and which ones are reflected by the chlorophyll molecule.

  3. Exercise #6 PHOTOSYNTHESIS PROCEDURE In order to study the absorbance of various wavelengths of light by chlorophyll, you must first separate the pigment from the leaf tissue. This is accomplished by following the procedure below: 1) Place a large spinach leaf into a 50 ml beaker and add 30 ml of ethanol. 2) Place the beaker with ethanol on a hot plate and slowly heat the solution taking care not to crush the leaf or boil the ethanol solution. 3) As the chlorophyll exits the leaf tissue it will enter the ethanol solution and turn the color green. 4) Fill the cuvette approximately 2/3 full will the chlorophyll extract. Refer to the diagrams on the right for a representation of the chlorophyll extract.

  4. Exercise #6 PHOTOSYNTHESIS At this point, we wish to determine which wavelengths of light are absorbed by the chlorophyll extract. However, we must first ensure that the concentration of chlorophyll in the solution is appropriate for the experiment. To do this, follow the procedure below: 1) Set the spectrophotometer at 550 nm and depress the %T button. 2) Place a cuvette filled 2/3 full of ethanol into the sample compartment and calibrate to 100 %T. 3) In order to continue on with the absorption experiment you must obtain a reading between 65% - 85%. -If you have a reading below 65%, your experimental solution is too concentrated--what should you do to change its concentration. Once you have reached an appropriate %T reading you are ready to continue with the experiment.

  5. Exercise #6 PHOTOSYNTHESIS Use your chlorophyll extract along with an ethanol blank and determine the absorbance of the chlorophyll solution at various wavelengths. NOTE: the procedure employed here is identical to that used in the determination of the absorption spectrum for methylene blue (Exercise #3) -remember to zero the machine after you change each wavelength. In order to clearly visualize the actual absorbance characteristics of your chlorophyll extract, you will plot your data using graphic analysis. Remember that wavelength is the independent variable and that absorbance is the dependent variable. Indicate with arrows on the x-axis the wavelengths of light most strongly absorbed by the chlorophyll extract.

  6. Exercise #6 PHOTOSYNTHESIS LIGHT INTENSITY AND PHOTOSYNTHESIS In general, as the intensity of light increases, the rate of photosynthesis increases. How does one measure the rate of photosynthesis? As you should recall, oxygen is a by-product of photosynthesis. Therefore, the photosynthetic rate can be determined by measuring the rate of oxygen production by the plant. During this portion of the laboratory you will observe the effect of light intensity on oxygen production and then make a generalization on plant survival based upon the data you have collected.

  7. Exercise #6 PHOTOSYNTHESIS PROCEDURE To determine the effect of light intensity upon photosynthetic rate, you will conduct the following experiment: 1) Obtain a piece of Elodea 5 to 6 inches in length and place it in a test tube with the cut end up. 2) Fill the test tube with NaHCO3 (serves as a source of CO2) and plug with the rubber stopper containing the bent glass pipette an a syringe.---AVOID AIR BUBBLES! 3) The position of the fluid in the pipette can be adjusted by raising or lowering the plunger in the syringe 4) Prepare a second tube filled with NaHCO3 without Elodea to act as a control for temperature and pressure fluctuations. 5) Place both tubes in a beaker filled with room temperature water. 6) Place a lamp 75 cm from the experimental beaker and set up a heat filter (additional beaker) filled with tap water placed half way between the light source and the experimental beaker. Refer to the picture on the following slide for reference.

  8. Exercise #6 PHOTOSYNTHESIS The following movie represents the experimental setup for the light intensity experiment.

  9. Exercise #6 PHOTOSYNTHESIS PROCEDURE (continued) 75 cm - Move the lamp so it is 75 cm away from the experimental tubes and place the heat filter half way between the lamp and tubes. Wait 5 minutes for equilibration. Adjust the fluids in the pipettes so that they are at the 0.2 ml mark and recalibrate only when changing the distance to the light source. Record the position of the fluid in the pipettes at 2 minute intervals for 10 minutes. 50 cm - Move the lamp forward so it is 50 cm away from the experimental tubes and again place the heat filter half way between the lamp and experimental tubes. Wait 5 minutes for equilibration and adjust the fluid in the pipettes to 0.2 ml. Repeat the experiment and record your data in table 6.4. 25 cm - Repeat the equilibration, adjustments and measurements at the 25 cm mark. Record your data in Table 6.4.

  10. Exercise #6 PHOTOSYNTHESIS The changes observed in the tube containing Elodea are the result of two simultaneous happenings: 1) the production of oxygen by Elodea which will always result in an increase in volume, and 2) fluctuations in temperature and pressure, which is why the pipette is set at the 0.2 ml mark. To obtain a true reading of oxygen production, you must subtract the control reading from the Elodea reading.

  11. Exercise #6 PHOTOSYNTHESIS Graphic Analysis Plot all three cumulative movements of fluid as a function of time on a sheet of graph paper. It is suggested that different plotting symbols be used for each distance from the light source (e.g. * for 75 cm; + for 50 cm; and - for 25 cm). Using a clear plastic ruler, draw a straight line that best fits all points for each distance. Your lines should indicate that the greater the light intensity, the greater the rate of oxygen production by the plant.

  12. Exercise #6 PHOTOSYNTHESIS CONCLUSIONS 1) You have seen that plants contain photosynthetic pigments. 2) Such pigments (chlorophyll) absorb only specific wavelengths of light. 3) The amount of light that the plant is exposed to has an influence on photosynthetic rate.

  13. This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.

Related


More Related Content

giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#