Introduction
When we talk about the most important chemical reaction in the world, some may think it has something to do with nuclear bombs. For some, it might be the ageing of wine, and some romantic people might call love the most important chemical reaction in the world, whether they mean it literally or figuratively, but there is another chemical reaction that is actually more important than all of those I just mentioned, and that is Photosynthesis. Photosynthesis is indeed the most important chemical reaction in the world because it’s hard to imagine life without it, and photosynthesis is our topic for today in a new Word Power episode from English Plus Podcast.
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The Most Important Chemical Reaction in the World
After the cold gray of winter, spring brings a sense of freshness and renewal. The salutary effect of the new season has been celebrated in festivals and ceremonies for centuries. Perhaps more than anything else, the green sprouts that burst from the soil and gradually elongate upward reflect this annual renewal. After witnessing this phenomenon year after year, one might begin to take this rebirth of plant life for granted, In reality, however, it is quite amazing. A little sunny warmth, some water, soil, and seeds can endow a field with explosions of flowers and a dense green cover in just a few weeks. How can a field that was frozen in lifeless ice and snow in February produce such grandeur in April and May? How can an orchard that was bleak and bare in March produce bushels of fruit in September? And how does the harvest of this growth sustain almost all other life on earth year around?
These questions address the very core of life itself. Almost all life on earth is powered by energy imparted by the sun. Living things that make their own food, such as plants, are called autotrophs. These autotrophs capture energy from the sun and use it directly or store it for future use, Other organisms, called heterotrophs, eat autotrophs and extract the energy and nutrients stored in their cells. Thus, directly or indirectly, the energy that powers almost all life is derived from the sun. But what allows plants to change sunlight into the stuff of life?
Within the cells of plants are chemicals that cause reactions to take place. In this case, the key chemical is chlorophyll. It is critical to the most important chemical reaction in the living world—photosynthesis. During this seemingly simple reaction, solar energy and chlorophyll cause the carbon dioxide and water in the atmosphere to combine and form sugar and oxygen. But the reaction is not really as simple as it seems, for there are a number of steps. First a series of steps called the light reactions bind the energy of light into molecules that are later used to build sugar molecules. The solar energy is absorbed by chlorophyll and converted into chemical energy stored in the bonds of an intermediate compound. During this phase, water is decomposed, ultimately giving off oxygen and leaving hydrogen ions behind. This oxygen is then accessible to you and other living things.
Other steps in this process of photosynthesis do not require light energy and are therefore called the dark reactions. During this stage the energy from the intermediate chemical, the hydrogen ions, and carbon dioxide combine into simple sugars. These simple sugars and the atoms they contain are the building blocks from which almost all other living tissue is built. Photosynthesis is the pivotal chemical reaction of human existence. So long as we have it, we have the means to survive.
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