February 18, 2014

10th Biology Photosynthesis - New Syllabus

Photosynthesis is the process by which all green plants contains the green pigment called chlorophyll, which build up complex organic molecules from relatively simple inorganic ones using light as an energy source. The process is very complex and there are several steps as well as intermediary compounds that are formed.

Scientists had tried to formulate a simple equation for photosynthesis over the past 200
years. An equation that was readily accepted and is still widely used is the one formulated and proposed by C.B. Van Neil in the year 1931 which is as follows. His opinion was, “for each molecule of carbohydrate formed, one molecule of water and one molecule oxygen is also produced”. This is a very simplified equation and does not reflect the complexity of the process of photosynthesis yet we shall use it for now.

What would be the reaction to show that glucose (C6H12O6) is being synthesized?

Write down a balanced equation to show this. It is known that plants synthesize carbohydrates, the smaller simpler ones first and from which the more complex ones like starch and cellulose are synthesized. 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 find out whether plants produce carbohydrates by the process of photosynthesis.

Boil the leaf in methylated spirit over a water bath till it becomes pale-white due to the removal of chlorophyll . Observe the leaf. Spread the leaf in a dish and add a few drops of tincture iodine/ betadine solution on it. Again observe the leaf.

What do you see?
The presence of starch will be indicated by a blue-black colour. Do you think solar energy transforms into chemical energy by the process of photosynthesis?
Materials essential for the process of Photosynthesis What are the materials that you think would be essential for the synthesis of carbohydrates in the process of photosynthesis? (Hint: Equation proposed by Van Neil)

Do you think the equation tells us about all the materials involved?
It took scientists over 300 years to find out about them and still there are several materials involved in the process that we don’t know about.

Let us study how scientists worked to find out about some of the materials required for the process of photosynthesis.

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