Chlorophyll & Photosynthesis Reactions

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

What is photosynthesis? And how is chlorophyll vital to that process? Learn all about chlorophyll's role, and then take a quiz to see what you've learned.

What is Photosynthesis?

You put a seed in the ground, sprinkle a little water, and from that grows a gigantic tree. Trees grow over time in the same way as humans do, but unlike humans they don't eat food. They don't have jaws, or stomachs, or intestines. So how do trees create the energy they need to live?

They do it by a process called photosynthesis. Photosynthesis is a process where plants convert light energy from the Sun into sugar (glucose) that the plant can use for energy. For a plant to photosynthesize, it needs several things: light, carbon dioxide, and water. It gets light from the Sun, absorbing it through its leaves. It gets carbon dioxide gas from the air around it, breathing it in through tiny stomata, which are holes on the underside of each leaf. And it gets water from its roots, which is why you only have to water the soil to get a plant to grow.

The underside of leaves contain stomata
The underside of leaves contain stomata

Photosynthesis is a chemical reaction, and so like all chemical reactions, it has a chemical equation to describe it. That chemical equation looks like this:

Equation for photosynthesis
Equation for Photosynthesis

One thing you might notice about this is that it takes a lot of stuff to produce a single sugar molecule: it takes six carbon dioxide molecules and six water molecules. But you might also notice there is a byproduct: oxygen. Where as humans breathe in oxygen and give out carbon dioxide, plants do the opposite: they take in carbon dioxide and give out oxygen. That's why trees are sometimes described as the lungs of the Earth. Without them, humans wouldn't be able to breathe.

The Role of Chlorophyll

Plants that photosynthesize tend to be the same color: they tend to be green. The reason they're green is that the leaves contain a substance called chlorophyll. As we'll discover, chlorophyll is vital for photosynthesis.

While different plants perform photosynthesis slightly differently, the need for chlorophyll is the same. That's because it's chlorophyll that does the job of absorbing the Sun's light in the first place. Light contains tiny particles called photons. When one of those photons hits one of the molecules contained inside chlorophyll, it gives energy to the electrons orbiting the atoms that make it up. It gives those electrons so much energy they're able to escape their atoms completely.

This electron passes to a different chlorophyll molecule, and then to another molecule, and then another in a process called the electron transport chain. The steps that follow are super complex, but eventually glucose is produced. And this reaction was all fueled by the energy provided by the photons of light.

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