Science Project

Photosynthesi s

PHOTOSYNTHE SIS The process of synthesis or preparation of food by plants is called photosynthesis. The green leaves produce food in the presence of sunlight. For this , they use carbon dioxide from the air, water and minerals from the soil.

EQUATION

 The process takes place inside the cell in green plastids called chloroplasts.

The overall equation for photosynthesis is.  6CO2 +12H2 O Sunlight Chlorophyll  C6 H12 O6 +6H2O +6O2  Carbon dioxide+ water Sunlight Food +

During this process

 The light energy is converted into

stable chemical energy, carbohydrate.  This chemical energy is the energy available for the rest of heterotrophic organisms.  Also during this process oxygen is liberated and this oxygen is used for respiration by all aerobic organisms oxygen constitutes 21% of our present day atmosphere.  This process helps in maintenance of balance of CO2 and oxygen concentration in the atmosphere.

site of photosynthesis 

Chlorophyll pigments are mainly present in cell organelles, called plastid. In a crosssection of a leaf, plastids can be seen just below the upper epidermis in a tissue, called the palisade. Chloroplasts can be seen easily under a light microscope. But the finer details of the organelle surrounds the chloroplast.

 The synthesis of

carbohydrates requires two substances. These are carbon dioxide and water. Carbon dioxide is a gas, which is released into the atmosphere during respiration. The autotrophic plants utilize carbon dioxide, which enters the leaf through the stomata present on its surface. The aquatic plants use carbon dioxide dissolved in water.

photosynthesis

Mechanism of photosynthesis  The entire process of photosynthesis can be divided into two main stages. One is light dependent and called light reaction, while the other is not dependent on light and is called dark reaction.  The released hydrogen ions reduce the NADP molecule into NADPH, which is also used during dark reaction. It is important to note that oxygen released during photosynthesis comes

factors affecting photosynthesis A number of factors effect the process of photosynthesis, as a result of which productivity is effected. These areLight Carbon dioxide Temperature Water

light  Plants use a very small portion of the incoming solar radiation their pigment. The chlorophylls absorb mostly the blue and red regions of the spectrum. Experimentally, it has been demonstrated the rate of photosynthesis increases at the lower intensities.

temperature  Photosynthesis involves the activities of a number of enzymes. The enzymes function with in an optimum range of temperature. Low temperature has an inhibitory effect on the rate of photosynthesis because the activity of the enzymes is lowered. Increase in temperature initially accelerates the rate, but high temperature inhibits photosynthesis.

water Though the requirement of water for photosynthesis by a plants is very little, yet it is an important factor. It has been observed that the rate of photosynthesis is slow in water deficient conditions under water deficient conditions stomata remain closed to reduce transpiration. This restricts or stops the entry of Co2 into the leaves.

Carbon dioxide The rate of photosynthesis increases with an increases in carbon dioxide concentration up to a certain level. Beyond that, CO 2 concentration has no effect on the rate of photosynthesis. On the contrary, it may prove inhibitory.

PHOTOSYNTHESIS IN PLANTS Plants are autotrophy and capable of trapping solar energy and convert into chemical energy stored in carbohydrates. Leaves are the photosynthetic organs in plants. Chloroplast are more localized in leaves.

References • •

Microsoft Encarta encyclopedia deluxe 2005 Science Text Book for 10th class

SUB. TEACHER  Mrs. Jasmeet kaur Science Mistress  Mrs. Kiranjeet kaur Science Mistress