Science 46

Spectrophotometers are instruments that measure the absorbance of light of a certain wavelength by a liquid. Because color changes with wavelength of light, spectrophotometers can be used to note subtle changes in color. A standard spectrophotometer is shown in Figure 1.

Students were investigating the rate of cellular respiration (metabolism of sugar) in mitochondria of lima beans.

The students added DPIP, a blue chemical reagent, to each of their test tubes. As cellular respiration was carried out, this reagent changed from blue to colorless.

The students prepared three test tubes, as shown in Table 1. Each test tube was then inserted into the spectrophotometer and the absorbance was set to 600 nm, the wavelength best absorbed by DPIP. Every five minutes for twenty minutes, absorbances were measured for each tube.