Facts About Photosynthesis

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Synthesis of complex organic material which uses carbon dioxide, inorganic salts, light energy and water, (from sunlight) captured through light-absorbing pigments, known as chlorophyll and other necessary pigments.

It is a process in which plants convert light energy that they take from the Sun, to chemical energy as carbohydrates. Carbohydrate “carbon plus water,” means literally, a clear term for the sugar formed by combination of carbon dioxide (CO2) with water. This process begins when plant pigments absorb with photons. As these photons reach some reaction center which are made up of chlorophylls, light energy excites electrons by splitting of water molecules. A part of the energy released during this by the energized electrons is utilized for the production of adenosine triphosphate (ATP). It is then used for the production of carbohydrates from water and CO2. During this process, water is the source of both electrons as well as the oxygen gas. Photosynthesis produce food for all the living organisms, indirectly or directly, in every ecosystem. In addition to this, it utilizes CO2 and releases oxygen and hence becomes an obligatory relation in the carbon cycle.

When numerous microscopic pores are opened by plants, called stomata, to allow CO2 for the process of photosynthesis, they are at a risk of losing water by evaporation, through these openings. Plants will, at times close stomata or these openings, in order to save water for survival. This delicate equilibrium between preserving water and allowing CO2 has led to evolution of three main types of photosynthesis. Plants that choose any of these three pathways not only show different anatomies but easily adapted to different climates too.

Few types of plants convert CO2 into three-carbon sugar and are called carbon 3 plants. They are typically good to temperate regions, where weather is not very dry or hot and water is not a limiting factor generally. Examples of carbon 3 plants are crops like peas, wheat, and barley.

Other type of plants convert CO2 into four-carbon sugar and are thus known as carbon 4 plants. They are equipped with CO2 pump that concentrates CO2 inside leaves. This enables such plants to function photosynthesis even when their stomata, partially or temporarily close, to conserve water on a hot and sunny day. Therefore, carbon 4 plants, well adapt intense sunlight and high daytime temperatures with periodic water deficits. So, when water becomes a limiting factor, due to this reason these carbon 4 crabgrass often outcompetes carbon 3 lawn grass in the summertime. More examples of carbon 4 plants are corn, sugarcane, and sorghum.

Carbon 4 plants generally perform better than carbon 3 plants in sunny and hot habitats. Because operation of their CO2 pumps needs energy, however, in a moist and cooler habitat where water isn’t the only limiting factor, carbon 3 plants have advantage over carbon 4 plants. When water is abundant, there is no need to close stomata to conserve water.

Thus, the energy spent on pumping of CO2 by carbon 4 plants becomes wasteful. Plants utilizing the third type of photosynthesis are uniquely adapted according to desert habitats. Because of the scarce water, these plants do not afford to open their stomata during day time, at all lest they will dehydrate. Desert plants engaged in crassulacean acid metabolism (CAM), open their stomata to allow CO2 at night, and convert it into acids, and store in their vacuoles. They release the CO2 which was stored inside the acids during day time for use in photosynthesis. CAM plants adapt well to high daytime temperatures, intense sunlight, and quite low soil moisture of desert biome. Some familiar CAM plants are cacti, sedums and pineapples.

Both CO2 and water serve as vital raw materials for photosynthesis. Therefore, any change in climate that affects the availability of either of these substance will affect photosynthesis process.

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