Question

Study the graph which shows results of three different experiments P, Q and R.

Which factor was varied in all these experiments?

• A. Light intensity
• B. Rate of photosynthesis
• C. Both A and B
• D. None of the above

Answer 1

The correct option is A Light intensity

An optimum temperature ranging from 25${}^o$C to 35${}^o$C is required for a good rate. At temperatures around 0${}^o$C the enzymes stop working and at very high temperatures the enzymes are denatured. Since both the stages of photosynthesis require enzyme activity, the temperature has an effect on the rate of photosynthesis. In the atmosphere, the concentration of carbon dioxide ranges from 0.3 to 0.4 %. However, it is found that 0.1% of carbon dioxide in the atmosphere increases the rate of photosynthesis significantly. Low light intensity lowers the rate of photosynthesis. As the intensity is increased the rate also increases. However, after reaching an intensity of 10,000 lux (lux is the unit for measuring light intensity) there is no effect on the rate. Very high intensity may, in fact, slow down the rate as it bleaches the chlorophyll. Normal sunlight (usually with an intensity of about 100,000 lux) is quite sufficient for a normal rate of photosynthesis. If we compare curve P, Q, and R-curves, the CO${}_2$ concentration in curve P and Q are same which is less compared to curve R. Temperature in both curves Q and R is optimum which is more compared to curve P. The light intensity is different in all the three curves and optimum in curve R, very less in curve P and less in curve Q. So, the factor varied in all the three experiments is light intensity.

So, the correct answer is option A.