NS 1011: Introduction to Biology: Cells and Organisms

Photosynthesis

INTRODUCTION:

Photosynthesis occurs in the chloroplast, an organelle in plant cells which contains the molecule chlorophyll. Chlorophyll absorbs the energy of sunlight. That light energy is converted to chemical energy through the steps of photosynthesis.

The reactions of photosynthesis can be divided into two major types: light-dependent reactions and light-independent reactions. The light-dependent reactions convert energy from the sun into a form which the chloroplast can then use to make sugar from carbon dioxide, in the process producing oxygen as a waste product. The light-independent reactions use that energy to make glucose from carbon dioxide and water.
 

Part 1: Measurement of photosynthesis

Materials:

• test tube
• stopper fitted with bent glass tubing
• Aquarium plant cuttings
• 3% sodium bicarbonate solution
• beaker with water
• lamp (60 watt)

Procedure:

1. Place a generous quantity of aquarium plants with the cut side up in a test tube with a rubber stopper fitted with a piece of bent glass tubing.
2. Add 3% sodium bicarbonate solution, enough so that when the stopper is fitted onto the tube the solution fills the tubing to about 1/4 of the length of the horizontal portion.  Mark the meniscus on the tube with a marker.
3. Place a beaker of plain water next to the plant tube to serve as a heat absorber.  Place a lamp next to the beaker.  The tube, beaker, and lamp should be as close to one another as possible.  See picture below.

 



4. Turn on the lamp.  As soon as the edge of the solution in the tubing begins to move, time the reaction for 10 minutes.  Be careful not to bump the tubing or to readjust the stopper, or your readings will be altered.
5. After 10 minutes, mark the new meniscus point, and measure in millimeters the distance the meniscus moved.
6. Calculate the net photosynthesis in mm/min.  (Divide the mm of movement by 10 minutes.)

1. With the members of your lab group brainstorm variables which may affect the rate of photosynthesis.
2. Form a hypothesis about your variable.
3. Design an experiment to test your hypothesis.  The instructor can provide information about available materials you may need.
4. After discussing your plan with the instructor, perform your experiment.
5. Record all data.
6. Does your data support or refute your hypothesis?

Lab Report:

• Title: A few words which give a sense of the purpose of the lab.
  Minus 1 point if no title
• An introduction to photosynthesis: What is it?  Why do plants do it?  What are the reactants and products?  Include the chemical equation. 
  3 point
• A brief summary of procedures followed. 
  1 point
• An explanation of your experiment in part 2, including your hypothesis and why you think your variable will change the rate.  Is this experiment well controlled
  3 points
• All data.
  2 points
• Conclusions drawn from the data. 
  3 points
• Questions:   
  1. Why did the solution in the bent tube move?
  2. What  is the purpose of the sodium bicarbonate solution?
  3. What variables might affect the rate of photosyntesis?  Include the variable you tested as well as others. You may discuss this with other lab groups.

  2 points

• Metacognitive analysis of the lab: what worked, what didn't work, and why.  Did this exercise fit with your learning style?  What would you change? 
  1 point