Moving water from roots to leaves is a problem that the terrestrial plants have had to overcome. But, there is an advantage for the plant that grows its leaves on stems in high branches. Light can reach the leaves more easily which is important for Photosynthesis.
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Photosynthesis is an energy storing process that is important to animals, as well as plant.
Free energy from sunlight is captured and stores the sugars and starches in plant tissues.
The way the leaves are arranged in stem ensures that the plant takes maximum advantage of the available light.
The key to Photosynthesis is the Chloroplast. There are large numbers of Chloroplasts found in the middle tissue of the leaf. In lowlight, they are distributed fairly, evenly. But, bright light causes them to move to a less exposed position.
The most noticeable characteristic of Chloroplast is their green color. The color comes from a pigment called Chlorophyll which is concentrated in the greener.
We can show that without the Chlorophyll, Photosynthesis does not take place.
First, we boil the leaf to fix it. Then, we put it in the alcohol. Boiling the leaf in an alcohol removes the Chlorophyll.
A few drops of iodine soon reveals a blue black color which indicates where starch is present in leaf. We can see the starch only produced in the parts of the leaf that were green, that is, where chlorophyll was present.
Chemical analysis of Chloroplasts shows that Chlorophyll in the series of other compounds are organized in the Thylakoid membranes in a systematic way.
When light strikes the Thylakoid membranes, Chlorophyll and other associated pigments are oxidized which causes the release of electrons.
The electron flow initiated by this input of light energy is coupled with the formation of adenosine triphosphate or ATP. The reaction is known as the light reaction of Photosynthesis.
Because electrons are being lost form the Chlorophyll, they have to be replaced. The plant does this by splitting water molecules in using electrons from hydrogen, leaving oxygen as a waste product.
When water plants like Elodea are Photosynthesizing, it is easy to see the bubbles of waste oxygen being released.
ATP molecules are energy storing molecules. They provide the energy that enables the plant to combine carbon dioxide with other compounds to make sugars.
This activity occurs in the stomata of the Chloroplasts and does not require lot a light. It is therefore known as the dark reaction of Photosynthesis.
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