Read the passage and answer any of the four  questions from (a) to (e).  


Some experiments were carried out using Croton sp. plants to understand the process of  photosynthesis. It was observed that the leaves  of the plant exposed to light for longer duration  accumulated more starch. However, due to  presence of preformed starch in the leaves, it  was difficult to find the net productivity on a  fixed exposure to light source. Therefore, it was  necessary to obtain starch free leaves in the plant  before starting the experiment.  


(a) Which of the following would help obtain starch  free leaves in the plant?  

(i) Expose the leaves to blue light for 48 hours  before starting the experiment.  

(ii) Keep the plant in dark for about 48 hours  before starting the experiment.  

(iii) Remove starch from the leaves by exosmosis,  48 hours before starting the experiment.  

(iv) Keep the leaves to the red light for 48 hours before  starting the experiment. 



Croton sp. Plants are plants with leaves that appear to be not green due to higher concentration of other colour pigments in the leaves. But since chlorophyll is also present , they carry out photosynthesis normal ly. 

  • The food prepared by the plants in the presence of sunlight by the process of photosynthesis is stored in the form of starch .
  • Therefore, in order to obtain starch-free leaves , we can place the plant in the dark for 48hours 
  • Photosynthesis does not occur and no new starch is produced. 
  • The starch already present in the leaf will be utilized within these 48 hours to carry out various life processes of the plant.

Croton sp. plant has green as well as other color pigments-01.jpg

So, the correct answer is (ii) 

(b) After a period of illumination, the leaves were  boiled in alcohol to make them colourless. Which  of the following could be used to test the end  product stored in the leaves?  

(i) Cobalt chloride paper  

(ii) Litmus paper  

(iii) Iodine solution  

(iv) Copper sulphate solution  



When the leaves are boiled in alcohol, they lose chlorophyll, which is a green colored pigment, and become colorless.

  • The end product after photosynthesis is starch.
  • Starch is stored in the leaves 
  • It can be tested by adding iodine solution which gives a bluish black colour indicating the presence of starch in the leaf.


So, the correct option is (iii) Iodine solution 

Carbon dioxide is necessary for photosynthesis-01.jpg


(c) Some of the starch free leaves were coated with wax  on both the surfaces. The plant was maintained  under normal environmental conditions. At the  end of the experiment, the wax coated leaves are  likely to show  _____.  

(i) Accumulation of more water.  

(ii) Wilting of the wax coated leaves.  

(iii) Increase in sucrose accumulation.  

(iv) Decrease in number of chloroplasts  



Due to the presence of wax, the stomata are blocked and therefore, 

  • the exchange of gases 
  • transpiration is inhibited

This means, there is no exchange of gases or loss of water.


As a result, wilting of leaves takes place.

wax blocks stomata and inhibits exchange of gases and transpiration-01.jpg                      

So, the correct option is (ii) Wilting of the wax coated leaves.


(d) During the morning hours, using a fine blade,  an incision was made to the leaves such that the  phloem tissue was cut open. Analysis of the liquid  oozing out was found to contain high amount of:   

(i) Xylose 

(ii) Ribose  

(iii) Sucrose 

(iv) Galactose  



The transport of glucose occurs in phloem in the form of sucrose , therefore, the cell sap that oozes out contains sucrose.  


Thus, the correct answer is (iii)

(e) Why do plants coated with vaseline or wax do not  remain healthy for a long time? Give any two  reasons.  



Covering a plant in vaseline/wax blocks the stomata in the leaves/stem of the plant.  

These plants will not remain healthy for a long  time because:  

(i) They will not get oxygen for respiration.  

(ii) They will not get carbon dioxide for photosynthesis.  

(iii) Upward movement of water and minerals  would be hampered due to lack of  transpiration. 


wax blocks stomata and inhibits exchange of gases and transpiration-01.jpg

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo