Photosynthesis

Photosynthesis is the process by which carbon dioxide is combined with water to form sugars and oxygen.  It is the process required for virtually all food chains and food webs in ecosystems.  In this process both light and chlorophyll are required.  Because photosynthetic organisms require light and use it to make their own food, they are termed photoautotrophs.

In this subject only the word equation need be remembered. In chemistry, the bottom equation is the one you need.



Photosynthesis takes place in the chloroplasts of plant leaves.  Photosynthesis is not a single reaction but a series of light and dark reactions involving many steps. A more detailed description can be found at 

http://biology.clc.uc.edu/courses/bio104/photosyn.htm

In the lab, we performed experiments to show the need of light and chlorophyll for photosynthesis to occur.  The plant we studied was the geranium, which stores the products of photosynthesis as starch. Plants were placed under a lamp overnight or left in a dark cupboard for a few days.Typical results we obtained are shown below.

The result for the leaf on the left is similar to what we obtained to the plant under the lamp, while the one on the right were similar to the one in the cupboard.  In the absence of light, the leaf draws on any reserves it has in storage and consumes the stach.  Hence it does not stain with iodine.  The plant on the left not only carried out photosynthesis during the day, but continued on doing so in the night under the lamp.  As a result, starch levels were high and easily stained with iodine after treatment.

We also had varigated (varying colour/yellow-green) leaves to test.  Because the green zones of the leaf contain chlorophyll and the yellow areas do not, you would expect the only the green zones to stain with iodine.  Here's a result similar to ours.