lesson
Updated 6 days ago · 2 views
Every bite of food you have ever eaten is made of captured sunlight. How does a leaf reach out into thin air and lock radiant light into solid sugar?
To understand how plants pull off this trick, let's look at where the energy enters and where it ends up.
Trapping Light into Chemical Stores
During photosynthesis, green plant cells use the green pigment chlorophyll to absorb light from their surroundings. That light energy is used to react carbon dioxide and water to produce glucose and oxygen.
In 1779, Dutch physician Jan Ingenhousz discovered that submerged plants only produced gas bubbles when placed in bright sunlight, proving that light is the essential energy input driving the reaction.
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Why do chemists classify this process as endothermic rather than exothermic?
Why Photosynthesis Is Endothermic
An endothermic reaction is a chemical reaction that takes in more energy from the surroundings than it releases back out.
Breaking the strong chemical bonds in carbon dioxide and water requires a large amount of energy. When the new bonds in glucose and oxygen form, less energy is released than was absorbed, resulting in a net transfer of energy into the chemical energy store of glucose.
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Does this mean plants create brand-new energy out of nothing?