Question

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

What does this experiment tell you about the factors limiting the rate of photosynthesis in the regions A-B and B-C of curve R?

• A. A- B was light intensity and B- C was some other factor (cannot find from available data)
• B. A- B was temperature and B- C was light intensity
  
• C. A- B was some other factor (cannot find from available data) and B- C was light intensity
  
• D. None of the above

Answer 1

The correct option is A A- B was light intensity and B- C was some other factor (cannot find from available data)

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. Along with light intensity, other factors affecting the rate of photosynthesis are temperature, CO${}_2$ concentration etc. 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. But after certain point rate of photosynthesis is constant with increase in CO${}_2$ concentration. 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 above graph, the factors limiting the rate of photosynthesis in the regions A-B is the light intensity and B-C are other factors such as temperature and CO${}_2$ concentration.

So, the correct answer is option A.