Question

Explain the use of radioactive isotopes in the study of mechanism of photosynthesis in plants and hydrolysis of esters.

Answer 1

Solution:-

Use of radioactive isotopes in study of mechanism of-

• Photosynthesis in plants $\to$

A small quantity of Radioactive $C{\stackrel{\ast }{O}}_2$ containing radioactive oxygen $O^{18}$ is mixed with ordinary carbondioxide and the process is carried out. It has been found that oxygen gas evolved along with sugar formation is non-radioactive.

$6C{\stackrel{\ast }{O}}_2+6H_{2}O\rightleftharpoons C_6{H}_{12}{O}_6+6{\stackrel{\ast }{O}}_2$

Thus $O_2$ produced comes from water and not from carbondioxide.

• Hydrolysis of esters $\to$

The mechanism of ester hydrolysis can be studied by using water labelled with $O^{18}$. The hydrolysis of an ester by water enriched with radioactive oxygen is indicated as :

$RCOOR+H\stackrel{\ast }{O}H\rightleftharpoons RCO\stackrel{\ast }{O}H+R-OH$

Thus it is the acid and not alcohol produced which is radioactive confirming the above mechanism.