The purpose of this lab was to isolate the chloroplast from spinach and measure its size while determining if weed killers would inhibit electron transport. This was done by centrifuging homogenized spinach. After re-suspending the pellet in ice-cold 100 mM Tris (pH 8.0), 0.4 M NaCl, some solution was removed to use for examination under a microscope to estimate the number of chloroplasts in the homogenate and the size of the chloroplast. A series of solutions, some with DCIP, some with Diuron, and some with Atrazine were made with the homogenized spinach and kept under various light intensity, some in the dark, and some in normal light. Every 5 minutes the absorbance was taken for each of these solutions. The estimated size of the chloroplast we extracted was 1.8 nm. We had about 400,000,000 chloroplasts in our homogenate. And every cuvette except the blank, 1 and 2, had 400,000,000 chloroplasts. Cuvettes 1, 2, and the blank had 0 chloroplasts. Cuvettes that were places in the light generally had a higher absorbance in the light because the are undergoing photosynthesis at a faster rate. However, some of the cuvettes went down in absorbance that were placed in the light because they had herbicides in them. This would cause the plants that were under going photosynthesis faster to completely stop because the herbicide has more to inhibit. But, the plants in the dark did not have that same problem because they were not undergoing photosynthesis as much as the plants in the light so the herbicides did not have as much to inhibit. By adding these specific herbicides, the rate of electron did decrease. These herbicides induced electron transport and therefore cause the absorbance of the solutions to go down.

References
Biol 230w Laboratory Exercise #3: Isolation of Chloroplasts:
Salisbury, F.B., and Ross, C.W. (1985). Plant Physiology (Belmont, CA: Wadsworth