Light Wavelength & Photosynthesis

Background Information: Light is a form of energy referred to as electromagnetic radiation. It is both matter (photons) and energy. Visible light is actually a combination of different wavelengths. Passing light through a prism can separate these wavelengths and make them all become visible. Colors that we see represent what is reflected and transmitted. What we do not see is what is absorbed. A red shirt is red because of a chemical makeup that causes red wavelengths of light to be reflected and all other wavelengths to be absorbed. (A white shirt reflects all wavelengths and a black shirt absorbs all wavelengths.) In photosynthesis light acts as the required energy source needed to support a series of chemical reactions that ultimately leads to the manufacture of sugar. Light trapping photosynthetic pigments act like solar collectors and capture some of the light energy that strikes it. The energy captured is channeled to chemicals that support the chemical reactions needed for the formation of sugar.

Reactants Products light energy + chlorophyll + H2O + CO2 ---- Sugar + O2

There are several different pigments found in organisms capable of photosynthesis. In plants the most important photosynthetic pigment is chlorophyll. Chlorophyll is responsible for the green color of plants. Betacarotene is the orange pigment in plants and xanthophyll is the yellow pigment in plants.

Purpose: In this lab activity we will explore the impact of different wavelengths of light on the growth pattern of raddish seedlings. Plants tend to grow toward favorable conditions and away from less favorable conditions. Procedure : 1. Puncture 3 small holes into your film canister. Cover each hole with a different color of cellophane (red, blue, green). The color of the cellophane represents what will pass through and be reflected, and all other colors are absorbed by the cellophane. 2. Take a piece of paper towel and fold it several times into a small square that is about the same diameter as the cap of the film canister. (the thicker the folded paper the more water it will hold and the better your results will be) 3. Soak the folded paper towel in water until it is completely saturated 4. Force the paper towel into the open end of the cap 5. Get a single radish seed and place it in the middle of the paper towel and gently push the seed into the paper towel to create a depression that it can not roll out of. 6. Take the canister and place it over the cap that is resting on the lab bench. Push downward to snap the cap into place. Adjust the paper towel as needed to insure a tight seal. 7. Turn the cap so that there is a marker lined up with each hole in the side of the canister. (ie: single mark-red, double mark-green, triple mark-blue). The marks will enable you to identify which color was lined up after you remove the canister. Add marks to the cap if needed. 8. Put a small piece of masking tape on the bottom of the canister with the names of your team for identification. 9. Carefully put the film canister into the designated tray making sure you have not dislodged the seed from the depression.

PRELAB: Using a text book or the Internet, define the following terms: Autotroph, Heterotroph, Photosynthesis, Chloroplast, Thylakoids, Pigment, Chlorphyll, Betacarotene, Xanthophyll, ATP (adenosine tri-phosphate)

PROBLEM: What color of light will radish seed grow towards (green, blue, red)?

HYPOTHESIS: Based on your understanding of what visible light is and why we see what we see, make a hypothesis about how your radish plant will respond to the different wavelengths of light. WRITE THIS IN IF..THEN..BECAUSE..format.

CONCLUSION (ANSWER IN COMPLETE SENTENCES) 1. Explain the result you got, and explain why the plant grew towards that color light. 2. What makes plants appear green? 3. Why do leaves change color in fall? 4. What is photosynthesis, and how is it demonstrated in this lab?