What does chlorophyll do? Why this molecule is vital to life on earth – and how it makes plants appear green

What does chlorophyll do? Why this molecule is vital to life on earth – and how it makes plants appear green

We all know it's essential to the carbon cycle, but what exactly is chlorophyll and why is it so important? Stuart Blackman explains more

Published: January 2, 2025 at 12:30 pm

The function of chlorophyll is likely something we've all been taught in school biology classes, but some facts stay in our brains longer than others.

For example, most of us remember that the mitochondria is the powerhouse of the cell. But can you remember what chlorophyll is, and why it's so essential to the carbon cycle? We take a look at this brilliant molecule...

What is chlorophyll?

This influential molecule is built of carbon, hydrogen, nitrogen and magnesium atoms and plays a fundamental role in the planet’s ecology.

What does chlorophyll do?

Packaged into tiny structures, called chloroplasts, inside plants’ cells, chlorophyll absorbs light energy from the sun and kick-starts the process of photosynthesis, which converts it into the chemical energy that powers biological systems.

Microscopic footage of chloroplasts, which contain chlorophyll. Credit: BBC Universal, Getty

The sunlight energises electrons in the chlorophyll, which drive a chemical reaction between carbon dioxide (from the atmosphere) and water (from the soil) to produce energy-rich sugars and, as a by-product, oxygen.

Most of the oxygen is expelled into the atmosphere ready for inhalation by animals, which require it for respiration. A by-product of respiration is carbon dioxide, and as part of the ecological circular economy, this is exhaled by animals and taken up by plants as fodder for photosynthesis.

Why are plants green?

Chlorophyll is most absorbent of red/orange and blue/violet parts of the light spectrum. Green light, though, is reflected rather than absorbed, which gives vegetation its default colour.

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