Question

1. The chloroplasts for today’s experiment were in suspension. Suspensions tend to scatter light.

a. If light is scattered, it is not easily detected by the spectrophotometer. Would this result in a decrease in % transmittance, increase in % transmittance, or no change when compared to water without chloroplasts suspended in it. Why? (2 points)

b When the detergent sarkosyl is added to a suspension of chloroplasts, the %     transmittance increases even if everything else is the same in the tube. Why might this be? (2 points)

2 If you were performing these experiments alongside Robert Hill, how could you show that this process requires water but does not require carbon dioxide (a huge question to be answered at the time)? (4 points)

Answer 1

1 a. There is a decrease in % transmittance. The reason being, the chloroplast suspension scatter(deflect) the light and also pigments present in chloroplast absorb light to a certain extent which implies the light does not pass through it whereas water without chloroplast allows the light to pass through(i.e.do not scatter) hence there is a decrease in % transmittance in the former case.

b. Detergent sarkosyl causes the lysis of membranes of chloroplast which results in the release of all its contents. Hence it becomes denatured and scattering of light decreases increasing the % transmittance.

2. Robert hill demonstrated that plants produce oxygen by reducing water in the presence of light (light-dependent reaction) and not from water. This can be explained using the above experiments as follows:

Take two test tubes, add an equal amount of chlorophyll suspension(isolated chlorophyll in water) to each of them

add KOH(absorbs CO2) to one of the test tubes in order to remove CO2.

Subject both of them to light. the transmittance is the same in both of them showing that chlorophyll pigment absorbs light and helps reducing water to oxygen and this function is independent of presence or absence of CO2.