Biology▶▶Nutrition▶ Top Factors Affecting Photosynthesis Low light intensity lowers the rate of photosynthesis. As the intensity is increased the rate also increases. However, after reaching an intensity of 10,000 lux (lux is the unit for measuring light intensity) there is no effect on the rate. Very high intensity may, in fact, slow down the rate as it bleaches the chlorophyll. Normal sunlight (usually with an intensity of about 100,000 lux) is quite sufficient for a normal rate of photosynthesis.  Open and Closed Stomata Sub Topics 1. Carbon Dioxide Concentration 2. Temperature 3. Chlorophyll Concentration 4. Water 5. Pollution 6. Application 7. Compensation Point  Back to Top In the atmosphere, the concentration of carbon dioxide ranges from .03 to .04 %. However, it is found that 0.1% of carbon dioxide in the atmosphere increases the rate of photosynthesis significantly. This is achieved in the greenhouses which are enclosed chambers where plants are grown under controlled conditions. The concentration is increased by installing gas burners which liberate carbon dioxide as the gas burns. Crops like tomatoes, lettuce are successfully grown in the greenhouses. These greenhouse crops are found to be bigger and better-yielding than their counterparts growing in natural conditions. The following graph shows how different concentrations affect the rate of photosynthesis.  Light Intensity  Back to Top An optimum temperature ranging from 25oC to 35oC is required for a good rate. At temperatures around 0oC the enzymes stop working and at very high temperatures the enzymes are denatured. Since both the stages of photosynthesis require enzyme activity, the temperature has an affect on the rate of photosynthesis.  Graph Showing Effect of Temperature on Rate of Photosynthesis  Back to Top The concentration of chlorophyll affects the rate of reaction as they absorb the light energy without which the reactions cannot proceed. Lack of chlorophyll or deficiency of chlorophyll results in chlorosis or yellowing of leaves. It can occur due to disease, mineral deficiency or the natural process of aging (senescence). Lack of iron, magnesium, nitrogen and light affect the formation of chlorophyll and thereby causes chlorosis.  Back to Top Water is an essential factor in photosynthesis. The effect of water can be understood by studying the yield of crops which is the direct result of photosynthetic activity. It is found that even slight deficiency of water results in significant reduction in the crop yield. The lack of water not only limits the amount of water but also the quantity of carbon dioxide. This is because in response to drying the leaves close their stomata in order to conserve water being lost as water vapour through them. Pollution Back to Top Pollution of the atmosphere with industrial gases has been found to result in as much as 15% loss. Soot can block stomata and reduce the transparency of the leaves. Some of the other pollutants are ozone and sulphur dioxide. In fact, lichens are very sensitive to sulphur dioxide in the atmosphere. Pollution of water affects the hydrophytes. The capacity of water to dissolve gases like carbon dioxide and oxygen is greatly affected.  Back to Top Study of photosynthesis and the factors affecting it helps us understand the most important biochemical life sustaining processes. All plants and animals are dependent on the sun for energy. This energy is made available to them by the process of photosynthesis. Man, like other animals, is dependent on the plants for his food. Scientists are constantly working towards developing new varieties of crops which give better yield of crops. With the population explosion and resulting pressure on land resources, the percentage of land available for cultivation is reducing at an alarming rate. This means that in the restricted space, the crops have to yield more. All this has been possible so far with the understanding of the photosynthesis. Greenhouse plants and crops in unfriendly freezing conditions have been possible due to the study of the factors affecting photosynthesis. Studies have shown that there are a group of plants called the C4 plants which are more efficient in harnessing carbon dioxide from the atmosphere. Since the atmospheric level of the gas is only 0.3 to 0.4% and maximum crop yield is reported at 1% level, these plants are ideal for cultivation as they can draw maximum carbon dioxide from the atmosphere, greatly increasing the yield. One of the areas of current focus is the better understanding of the mechanism of C4 plants. Back to Top The rate of photosynthesis is not constant throughout the day. Its rate is affected by the intensity of light. The actual requirement of the light intensity for maximum photosynthesis in a plant depends on the type of plant and also on its habitat. Generally, average sunlight intensity is sufficient for photosynthesis except on rainy or cloudy days. The rate of photosynthesis increases with increasing intensity of light and decreases with decreasing intensity of light. During early morning or late evenings when the rate of photosynthesis becomes equal to the rate of respiration, there will not be any net exchange of gases (CO2 and O2) between the plant and the surrounding environment. The light intensity, at which the photosynthetic intake of carbon dioxide is equal to the respiratory output of carbon dioxide is called the compensation point
Posted on: Wed, 15 Oct 2014 10:30:34 +0000
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