FOHS Photosynthesis and Plant Physiology Name ________________________________ 1 Pre-lab Homework: Photosynthesis and Plant Physiology Read the lab carefully and complete the questions below before coming to lab! 1. This week's lab covers photosynthesis and basic plant physiology. Read the lab, find the summary equation for photosynthesis and write it below. Photosynthesis summary equation: 2. During the first part of the lab you will be testing for starch in plant leaves. Why are we testing for starch? 3. In our first experiment, we have placed black paper on some of the leaves. Why would we put on paper that we think blocks all of the light? 4. In the second experiment we are separating pigments by paper chromatography. Other than chlorophyll, what pigments might we find in the spinach leaves? 5. In the third experiment we are examining gas exchange in plant leaves. What differences do you predict you’ll see between the plant kept in the light versus the plant kept in the dark?FOHS Photosynthesis and Plant Physiology Name ________________________________ 2 Photosynthesis and Plant Physiology GOALS: After successfully completing this lab, a student will be able to: • List some of the factors that affect photosynthetic rate. • Explain the connection between light and energy storage in plants. • Examine gas exchange in plant leaves • Use the scientific method to investigate biological processes. • Calculate the Student’s t-test to compare two data sets OVERVIEW: During this lab you will perform experiments to help you understand two of the basic processes that convert energy from one form to another in biological systems. Your investigations will begin with experiments on photosynthesis. Photosynthesis is the process that plants use to convert the energy of light into the stored chemical energy of sugars. Photosynthesis can be summarized with an equation that looks like this: 6CO2 + 6H2O ————>C6H12O6 + 6O2 Light Looking at this summary equation, you can probably guess that many factors affect the rate of photosynthesis. As with any reaction, changing the concentration of the reactants (carbon dioxide and water) or the products (glucose and oxygen) can alter the rate of the reactions. In this lab, we will investigate the role of light in controlling the amount of photosynthesis. As in any scientific experiment, we will try to isolate one variable, in this case the wavelengths of light, and see what effect these have on the amounts of photosynthesis in leaves. The wavelengths of light correspond to different colors. EXERCISE 1: Photosynthesis and light Plant cells convert carbon dioxide into carbohydrates in a process called photosynthesis. Recall that the equation looks like this: 6CO2 + 6H2O ————>C6H12O6 + 6O2 Light To investigate this process we need to have some way to measure the amount of the sugar glucose produced by a plant. We will use a closely related compound, starch, which is produced by plant leaves as an energy storage product when they have excess sugars. To see the starch, we will use an indicator called Lugol's solution. This solution, which contains potassium and iodine, stains starch a darkFOHS Photosynthesis and Plant Physiology Name ________________________________ 3 purple/black color, but does not stain sugars such as glucose. To look for the presence of photosynthesis, we will test for the presence of starch using Lugol's solution. Any part of the leaf that stains a dark color indicates the presence of starch and therefore that photosynthesis has been happening at such a rate that excess sugars are produced. Using the Lugol's solution starch test, we will examine the effects of different wavelengths of light on the ability of plants to perform photosynthesis. A week ago, four filters of different colors were placed on the leaves of geranium plants. One filter is just black construction paper and should block all of the light to the leaf underneath it. The other three filters are colored translucent plastic films that let through only certain colors of light. For example, the red filters let only red light through to the leaf, the blue only blue light, and the green only green light. By using these filters we are able to alter the independent variable, in this case the color (or wavelengths) of the light, and see how it affects the dependent variable, in this case the amount of starch produced. The black construction paper absorbs all of the light and so appears black. Your jeans appear blue because they absorb all light except for blue. Your jeans reflect blue light. The plastic filters reflect and transmit the colors they appear and they absorb all the rest. These wavelengths do have energy, which is why the filters breakdown and dyed fabrics fade over time. Questions: What is your hypothesis regarding the effect of different wavelengths on photosynthesis? What are some other variables that you can think of that could affect the amount of photosynthesis in these plants? Brainstorm as many as you can think of! Pick two of these variables from the previous question and explain how we controlled for them.FOHS Photosynthesis and Plant Physiology Name ________________________________ 4 This procedure involves heating a highly flammable liquid. You need to be very careful and follow instructions carefully! PROCEDURE FOR STAINING STARCH IN LEAVES: 1. Set up a beaker of boiling water for your alcohol bath. To do this, add 200 ml of tap water to a 600 ml beaker and place it on your hot plate as shown in Diagram A. Turn the hot plate to high. The hot plate will get HHOOTT - please be careful! 2. Now place approximately 100 ml of 80% ethanol in a 250-ml beaker and carefully set this beaker into the water beaker before the water boils (see Diagram B). When the water begins to boil, turn down the hot plate until the water maintains a slight boil. 3. While the alcohol is warming up, remove the leaf (or leaves) assigned to your group and take them back to your desk. Do not remove the filters! A B C From Explorations in Basic Biology, tenth edition by Stanley E. Gunstream, 2005, page 79, Courtesy of Prentice-Hall, Inc. 4. Before you remove any of the filters, sketch your leaf face up so that after you boil