Question

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

Which factor has been changed to produce the difference(s) you can see between curves P and Q?

• A. Temperature is higher in P
• B. Temperature is lower in Q
• C. Temperature is higher in Q
• D. Temperature is lower in P

Answer 1

The correct option is C Temperature is higher in Q

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 affect on the rate of photosynthesis. In the atmosphere, the concentration of carbon dioxide ranges from .03 to .04 %. 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 and Q, both light intensity and CO${}_2$ concentrations are less in curve P and Q which acts as limiting factors. But, the temperature in curve Q is 25${}^o$C which is more than curve P which made the rate of photosynthesis in curve Q a bit higher than curve P. So, temperature also acts as limiting factor in curve P.
So, the correct answer is option C.