Photosynthesis

Photosynthesis is defined as the production of complex organic materials, especially carbohydrates from carbon dioxide, water, and inorganic salts, using sunlight as the source of energy and with the aid of chlorophyll and associated pigments.

Photosynthesis occurs in leaves and in the green stems of plants. Each cell in a plant leaf has 40 or 50 chloroplasts, divided by thylokods which contain molecules of chlorophyll, the pigment that traps light for photosynthesis. The process of photosynthesis is divided into two stages: the light-depended reaction and the light-independent reaction. Melvin Calvin's work focused primarily on the light-independent reaction.

This process involves carbon dioxide entering plant through the pores in the leaves diffusing through the cell into the chloroplast, and scattering in the stroma. In the stroma, the light-independent reaction takes place. This reaction is also called the Calvin cycle in honour of the man who explained it. During the experiment, he found that when he removed the light source over the plants, some of the cells continued to be active. As a result of this discovery, he deduced that part of the process was not dependent on light. Using ion-exchange chratography, he found that the primary compound was the three-carbon compound.

Photosynthesis plays a very important role in evolution. One of the first organisms of earth was the cyanobacteria. It carried out photosynthesis and evolved into more complex organisms. In order for animals to develop, plants had to be established. Animals are unable to produce glucose for energy so they must obtain it from plants. A by-product of photosynthesis is the oxygen that animals breathe. Thus, without photosynthesis, life on earth would cease to exist. Virtually every organism on earth is dependent on photosynthesis in one way or another. Because of these vital uses, photosynthesis is one of the most important processes on the earth.

(Adapted from the Internet sites)

6.3 Read the text to know more about Antoine-Laurent Lavoisier.

Дата добавления: 2015-08-03