Light is an essential factor in the process of photosynthesis, since it is light that triggers the reaction mechanism. Photosynthesis can be broadly divided into two sections, the light dependent reactions and the light-independent reactions. All the light dependent reactions are carried out before the light-independent reactions. The first step of the light dependent reaction of the absorption of light. The absorption of photons of light causes electrons within the chlorophyll molecules to jump to higher energy state, these 'excited' electrons are then transported through the phtosystems i.e. groups of hundreds of molecules of chlorophyll to a special chlorophyll molecule at the center of the photosystem. There are two kinds of photosystems, photosystem I (PS I) and photosystem II (PS II). This molecule is responsible for passing these 'excited' electrons to a chain of electron carriers. The process that follows this is the production of ATP. 'Excited' electrons are passed through a series of electron carriers; these electrons lose some energy every time they pass from one carrier to the next. Eventually, enough energy is released to produce one molecule of ATP. After releasing the energy required to make one ATP molecule, the electrons are accepted by PS I. At this stage PS I also absorbs light and the electrons are once again elevated to the 'excited' state. These high-energy electrons now pass through a series of electron carriers to NADP+ present in the stroma. The NADP+ ion accepts two of these 'excited' electrons as well as one H+ ion from the stroma in order to form NADPH. The next process that occurs is photolysis i.e. the splitting of water due to light. As a result of this process oxygen is produced as a byproduct and is hence excreted out of the plant through the stomata.
The process that follow are all part of the light independent reaction, these processes include the Calvin cycle, a process through which a five-carbon sugar is formed, namely ribulose bisphosphate (RuBP). This sugar reacts with carbon dioxide that enters the stroma of the chloroplast by diffusion to form a six-carbon compound called glycerate 3-phosphate. This is followed by a reduction reaction that causes the glycerate 3-phosphate to be converted to a carbohydrate triose phosphate. The linking together of two Triose phosphate molecules produces glucose phosphate. The condensation of many molecules of glucose phosphate forms starch, the main end product of photosynthesis.
It is the production of starch within the chloroplasts of the plant that facilitates the growth and development of plants. Hence a relation can be drawn between the growth of plants and the nature of the light to which the plant is exposed.
A schematic diagram showing the different processes involved in photosynthesis.
Hypothesis- The rate of photosynthesis will be greater if a plant is exposed to violet light (400-450 nm) or red light (630-700nm) as compared to green light (510-550nm). This is so because the
Light Spectrum
Apparatus List-
1. X Plant
2.7 Water Troughs
3.pH meter
4.Digital Balance
5.Thermometer
6.100 cm3 measuring cylinder
7. 6 large boxes
8.60 W colored bulbs (Violet, Blue, Green, Yellow, Orange and Red)
9. 6 Lamps
10.Measuring Cylinder
11.Lap Pro
12.Scissors
13.Water
www.gamonline.com/catalog/ colortheory/visible.php, 05/12/2004
