Explain how paper chromatography is used to separate the light-absorbing pigments in a leaf. Prepare and interpret a chromatogram.
Lab 4 – Photosynthesis 9
Almost all life on earth depends directly or indirectly on photosynthesis: the ability of certain organisms (notably green plants) to capture and store the energy of sunlight. Photosynthesis in green plants involves a complex series of reactions, but the overall process uses carbon dioxide and water to make glucose (a simple sugar) and other carbohydrates, with oxygen as a by-product. sunlight
6 CO2 + 12 H20 —————-> C6H12O6 + 6 O2 + 6 H2O
The sun’s energy is stored in the bonds that hold the glucose molecule together. Photosynthesis occurs inside the green, chlorophyll-rich cell organelles called chloroplasts. Inside the chloroplasts are stacks of “thylakoids” (flattened sacs), aligned to keep the light-absorbing chlorophyll exposed to sunlight. The energy stored in the glucose can later be released by a process called respiration. Respiration involves another complex series of steps, but the overall reaction is roughly the reverse of photosynthesis:
C6H12O6 + 6 O2 —————–> 6 CO2 + 6 H2O + Energy
During respiration, glucose is broken down into carbon dioxide and water. The energy stored in the glucose is released gradually, a little at each step, and stored in small ATP molecules. The ATP’s then carry the energy to wherever it is needed inside the cell. Respiration occurs inside mitochondria, which are cell organelles packed with internal membranes in which the enzymes of respiration are embedded. This minicourse focuses on photosynthesis the effects of environmental factors on the rate of this enzyme-catalyzed reaction.
Lab learning objectives
You will have mastered the content of this minicourse when you are able to:
1. Explain how paper chromatography is used to separate the light-absorbing pigments in a leaf. Prepare and interpret a chromatogram.
2. Given a leaf cross section, identify the major cell layers and explain in what way(s) each layer aids photosynthesis by the chloroplasts.
3. Analyze and discuss the results of experiments concerning the effects of the environment and osmosis on guard cells and stomata.
4. From your own experiments and data from others, describe how the rate of photosynthesis is affected by the following factors: the availability of carbon dioxide, light intensity, light quality, temperature and/or pH.
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5. Given what you know about the molecular properties of enzymes, explain why the rate of photosynthesis should be affected by each of the environmental factors listed above.
PLAN AHEAD! You will need to work with a partner for lab #4. A lab report is NOT required this lab.