Van Neil first worked on purple sulphur bacteria and found light plays a specific role in photosynthesis. Instead of H2 O they used H2 S as a starting material. Here no oxygen is liberated during photosynthesis instead, elemental sulphur is evolved. Later he envisioned a similar process of photosynthesis in plants and proposed the above mentioned equation. Later Robert Hill showed that O2 is released from water during this reaction. Then the equation was modified as follows.

6CO₂  + 12H₂O  Light/Chlorophyll C₆ H₁₂O₆   + 6H₂ O + 6O₂

It is known that plants synthesize carbohydrates, the smaller simpler ones first and from them, the more complex ones like starch and cellulose.

Plants are also capable of synthesizing all other compounds like proteins, fats etc.

Animals are not capable of synthesizing carbohydrates and they have to depend on plants for the same. Can we state that photosynthesis is the basic energy source for most of the living world? Why, why not? Let us study how the plants prepare carbohydrates through photosynthesis.

Activity 3

Presence of starch (a type of carbohydrate) in leaves