Life Science Lab (sec. 801)
March 11, 2011
Introduction Page 3
Procedure and Results Page 4
Data Results Page 6
Explanations and Conclusions Page 7
References Page 8
Photosynthesis Questions and Answers Page 9
Why do we care about photosynthesis?
Photosynthesis is not only important to the survival of plants, but to the existence of most of life on Earth. Green plants are a vital part of the circle of life because they ultimately provide food for consumers (organisms that rely on eating other ...view middle of the document...
Note: In the fall season, when there is less sunlight to produce chloroplasts, the leaves absorb all colors but yellow and orange.
Chloroplasts contain stroma, which is the fluid within the membranes, and thylakoids, which are flattened sacs. Within the thylakoids membrane are chlorophyll and carotenoids. The job of chlorophyll is to absorb solar energy. The absorption of solar energy for photosynthesis is called a “light” reaction. Complexes in the thylakoid membranes convert the solar energy from the sun into a chemical form useable in the stroma. Stroma is an enzyme-rich solution that takes an organic compound and carbon dioxide, and then reduces it to a carbohydrate using the chemical energy produced by the thylakoid membranes. ATP is also produced in the thylakoid membrane and is a source of energy for the plant to grow.
The carbohydrate produced by the stroma is the only energy source for most organisms on Earth. When consumers metabolize this carbohydrate, it is converted and released as carbon dioxide back into the atmosphere. Plants take in the carbon dioxide through stomata, which will be converted into a carbohydrate again. This relationship between producers (and photosynthesis) and consumers (and respiration) is a vital part of Earth’s life cycle.
In addition, it is important to note that photosynthesis is made up of two separate reactions. The first is “light” reactions, which were discussed above, and also “dark” reactions (Calvin Cycle). “Dark” reactions are light independent, which means they can happen during either sunlight or at night. The Calvin Cycle (“dark” reactions) uses the energy produced by the “light” reaction to reduce carbon dioxide with hydrogen and carbohydrate.
In this laboratory, we performed experiments that explored the importance of light, oxygen, chlorophyll, carbon dioxide, and stomata in photosynthetic reactions.
II. Procedure & Results
Necessity of Light for Photosynthesis
For this experiment, Geranium plants were kept in either light or dark for 48 hours prior to the laboratory. A leaf from each plant was tested for the presence or absence of starch by the following procedures:
I. First, we removed a leaf from a plant that had been kept in the dark for 48 hours and a leaf which had been exposed to sunlight for 48 hours. To distinguish the “dark” leaf from the “light” leaf, we cut the leaves into different shapes to tell them apart.
II. Next, we boiled both leaves in water for 10 minutes. This loosened up the cell walls in the leaf.
III. Then, we replaced the boiling water with alcohol and heated the leaves for 1 minute. The alcohol helped to pull out sugars from the leaf.
IV. Lastly, we placed the two leaves in a petri dish added an iodine solution. The iodine will turn the leaf bluish-black if starch is present, which will indicate the presence of sugars.
Release of Oxygen
Oxygen release may be used as a measure of the effect of light...