The simple story of photosynthesis and food - Amanda Ooten

Transcriber: Andrea McDonough
Reviewer: Bedirhan Cinar

Ever wonder where most of the food you eat every day comes from? Well, about 60% of the food you eat is carbohydrates. As you can probably tell from its name, carbohydrates contain carbon, hydrogen, and oxygen. But where do these atoms originally come from, and how do they join together to make delicious foods like fruits and pasta? It actually all starts with the air you are exhaling this very minute, specifically the carbon dioxide molecules.

Plants are going to breathe in this very same carbon dioxide through pores in their skin, called stomata. Plants drink in water from their roots to get the needed oxygen and hydrogen atoms, and their electrons, in order to build carbohydrates. What is that thing? Well, that's a special plant organelle inside the leaves of plants called a chloroplast. It's green because of a special light-absorbing pigment called chlorophyll. Each leaf has about 44,000 cells, and every cell can have anywhere between 20 to 100 chloroplasts. That's up to 4,400,000 chloroplasts!

By now, you've probably guessed that we're talking about the process of photosynthesis, and you might be wondering when the sun is going to make its entrance. Let's go back to that original molecule of water. The plant has to split this molecule of water so it can get electrons from it. But the plant can't pull that water apart by itself. It needs help from the high-energy rays of the sun.

So now that the chloroplast has all the building blocks - carbon, hydrogen, oxygen, and electrons - it can use them to go through the rest of the steps of photosynthesis to transform that original carbon dioxide gas into a simple carbohydrate called glucose, C-6-H-12-O-6. That little glucose molecule then helps to build bigger and better carbohydrates like cellulose. Cellulose is a type of carbohydrate found in plants that our body cannot break down. We call it fiber, and we eat it in vegetables like lettuce, broccoli, and celery.

Plants use cellulose to keep themselves strong. The plant could also turn that glucose into starch, a large molecule that stores energy for the plant. We love eating starch from plants like potatoes, corn, and rice. So you see, when you eat plants, we're actually benefiting from photosynthesis. The plant makes things like starch, which we eat and then break back down into glucose, the first form the plant made.

Then, the mitochondria in our cells, powered by the oxygen we breathe, can turn glucose into pure energy molecules called ATP. ATP powers all work done by each and every one of your cells, things like communication, movement, and transport. But why do we have to turn that glucose into ATP? Well, think of it like this. You're excited to start your summer job at the local ice cream stand, but your boss has just told you that she is going to pay you in ice cream cones. What are you going to be able to do with those ice cream cones? Nothing, which is why you kindly asked to be paid in dollars.

ATP is just like dollars. It is the currency that all cells of life use, while glucose is, well, kind of like ice cream. Even plants have mitochondria in their cells to break down the glucose they make into ATP. So as you can see, humans and plants are intricately connected. The air we breathe out is used by plants to make the carbohydrates we enjoy so much. And, in the process, they are releasing the very same oxygen molecules we need to breathe in, in order that our mitochondria can break down our delicious carbohydrate meal.