Photosynthesis

Photosynthesis- is a chemical reaction that uses light energy and chlorophyll to trap energy in the bonds of glucose.

Formula:

                                                                    Reactants:                                                 Products:

The formula is read as:

Carbon dioxide and water in the presence of light and chlorophyll yields glucose, oxygen, and water.

Count the number of each of the following atoms on the reactant and product sides.

                    Reactants Side:                     Product Side:

                    Carbon: _______                     Carbon: _______

                    Oxygen: ______                     Oxygen: ______

                    Hydrogen: _____                     Hydrogen: _____
 
 
 
 

It was found that the Oxygen produced in photosynthesis came from the water in the reaction, not from the Carbon dioxide. Also, the Oxygen contained in the Carbon dioxide are used to make the glucose and water. Look at the chart below and trace the path of the Oxygen from the reactants to the products.

Challenge: Use the Internet to find out how this was discovered and who discovered it (5 pts. Extra Credit). ___________________________________________________________________________

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Photosynthesis is not really one singe reaction; it is two, the light reaction and the dark reaction.

Light Reaction:

In the light reaction, the energy of sunlight is used to split the bonds of the water molecules and Oxygen is released.

Dark Reaction:

In the dark reaction, the 12 molecules of Hydrogen help to make 18 ATP (adenosine triphosphate) which provides energy for the reaction. Carbon dioxide and the Hydrogen are used to make the glucose and water. The dark reaction does not require light.





Although it would be difficult to observe photosynthesis in its entirety, we can explore various aspects in the laboratory. Over the next several class period we will perform the following experiments:


 

Lab: Stomata in Leaves

Question: What structure in a plant regulates the passage of Carbon dioxide and water into and out of the leaf, and how is this accomplished?

Materials:

Plant leaves     coverslip     microscope slide     microscope

5% NaCl solution     tap water     eye droppers     (2) small beakers

(1) large beaker

Procedure:
1.  Make a wet mount of the plant leaf with the bottom of the leaf facing up
2.  On medium power, scan the field of view and count the number of stomata that are open. Record in data table.
3.  Position one of the stomata at the tip of the pointer and move the revolving nose piece to high power. In the data table, draw what is observed, labeling      the stomata and guard cells.
4.  Rotate the revolving nose piece back to low power.
5.  Place a small paper towel on the left side of the slide so that it just touches the edge of the cover slip. This will absorb and draw the tap water from between the slide and cover slip. At the same time, place one to two drops of 5% NaCl solution on the right side of the slide just at the edge of the cover slip. The salt solution will be drawn under the cover slip (You may remove the slide from the stage and make another wet mount using the 5% NaCl solution if you have difficulty).
6.  On medium power, scan the field of view and count the number of stomata that are open in the 5% NaCl solution. Record in data table.
7.  Position one of the closed stomata at the tip of the pointer and move the revolving nose piece to high power. In the data table, draw what is observed, labeling the stomata and guard cells.
 

Data:
 
  Tap Water 5% NaCl Solution
Number of Stomata Open    

Wet mount of leaf                                         Wet mount of leaf                             in Tap Water                                                 in 5% NaCl solution

                                                    
 
                           _______X                                                         ________X

Conclusions:

How would you expect to find stomata during a drought?

____________________________________________________________________________

What can you infer about the function of the stomata in a leaf?

____________________________________________________________________________

Hypothesize how a stomata opens and closes, using the information you learned from the lab on osmosis. ____________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

Diagram the osmotic effect of the guard cells in the 5% NaCl solution.
 
 
































































Lab: Reactants of Photosynthesis

Question:

Can it be shown that carbon dioxide is use in photosynthesis?

Background notes:

Bromothymol blue is an indicator of pH. It is blue in a base and yellow in an acid. When carbon dioxide is added to water it reacts to form carbonic acid. This turns the bromothymol blue yellow. If the carbon dioxide is removed, the solution becomes more basic and turns back to a blue color.

Materials:

Large flask Water Straw Cork

Bromothymol blue Elodea

Procedures:

  1. Add 300mL of water to the large flask.
  2. Add 30 drops of bromothymol blue to the flask. The water should turn blue.
  3. Using a straw, blow bubbles into the solution until it changes to a yellow color.
  4. Place one 8cm green sprig of Elodea into the flask and cork the flask.
  5. Place the flask in direct sunlight or under a grow light for approximately 60 minutes.
  6. After 60 minutes, record your observations.
Data:

Color of solution at the beginning of the experiment _____________________

Color of solution at the end of the experiment _____________________

Conclusions:

What were you adding to the water as you blew bubbles into it?

___________________________________________________________________________

What caused the bromothymol blue to turn yellow?

____________________________________________________________________________

What caused the color change at the end of the experiment?

____________________________________________________________________________

What happened to the carbon dioxide in the water by the end of the experiment?

____________________________________________________________________________
 
 


Lab: Reactants of Photosynthesis

Question:

Can it be shown that carbon dioxide is use in photosynthesis?

Background notes:

Bromothymol blue is an indicator of pH. It is blue in a base and yellow in an acid. When carbon dioxide is added to water it reacts to form carbonic acid. This turns the bromothymol blue yellow. If the carbon dioxide is removed, the solution becomes more basic and turns back to a blue color.

Materials:

test tube Water Straw Cork

Bromothymol blue Elodea test tube holder

Procedures:

  1. Place the test tube in the test tube rack and fill 2/3 with water.
  2. Add 5-10 drops of bromothymol blue to the test tube. The water should turn blue.
  3. Using a straw, blow bubbles into the solution until it changes to a yellow color.
  4. Place one green sprig of Elodea that is _ the length of the test tube into the test tube and cork it.
  5. Place the rack and test tube in direct sunlight or under a grow light for approximately 60 minutes.
  6. After 60 minutes, record your observations.
Data:

Color of solution at the beginning of the experiment _____________________

Color of solution at the end of the experiment _____________________

Conclusions:

What were you adding to the water as you blew bubbles into it?

___________________________________________________________________________

What caused the bromothymol blue to turn yellow?

____________________________________________________________________________

What caused the color change at the end of the experiment?

____________________________________________________________________________

What happened to the carbon dioxide in the water by the end of the experiment?

____________________________________________________________________________