What Is Chlorophyll?
Chlorophyll is a green pigment found inside chloroplasts in plant cells. A pigment is any substance that absorbs certain wavelengths of light. Chlorophyll is the most important pigment in plants because it captures the light energy needed to drive photosynthesis.
The word chlorophyll comes from two Greek words: chloros (green) and phyllon (leaf). It accounts for the green colour of leaves, stems, and other plant parts that are exposed to sunlight.
Which Light Does Chlorophyll Absorb?
Sunlight appears white but is actually a mixture of all colours of the visible spectrum. Chlorophyll absorbs light most strongly in the red and blue wavelengths. It reflects green light, which is why we see leaves as green.
Red light has a longer wavelength; blue light has a shorter wavelength. The energy absorbed from these wavelengths is used to power the light-dependent reactions of photosynthesis.
If leaves only used chlorophyll for photosynthesis, they would waste all the green and yellow light hitting them. Other pigments make up for this by absorbing different wavelengths.
Other Photosynthetic Pigments
Plants contain more than just chlorophyll. A group of accessory pigments work alongside it:
Carotenoids — Yellow and orange pigments (e.g., carotene and xanthophyll). They absorb blue-green light and pass the energy to chlorophyll. They also protect chlorophyll from being damaged by very bright light.
Anthocyanins — Red and purple pigments found in some leaves, flowers, and fruits. They are not directly involved in photosynthesis but may protect cells from UV light and deter pests.
In autumn, as chlorophyll breaks down, the yellow and orange carotenoids (which were present all along but hidden) become visible — giving leaves their beautiful autumn colours.
Types of Chlorophyll
There are two main types used in plants:
Chlorophyll a — The primary pigment, directly involved in the light reactions. It absorbs mainly blue-violet and red-orange light and reflects green-blue light.
Chlorophyll b — An accessory pigment that absorbs blue light slightly differently and passes energy to chlorophyll a. It appears yellow-green.
You can separate plant pigments using a technique called paper chromatography. When a leaf extract is placed on special paper and a solvent travels up the paper, different pigments travel at different speeds and separate into visible coloured bands.
Why Multiple Pigments?
Having a range of pigments means plants can absorb a wider range of light wavelengths. This makes photosynthesis more efficient, especially in shaded environments where only certain wavelengths of light are available (for example, under the canopy of a forest where blue-green light dominates).
Real world: Autumn leaf colour
Every autumn, deciduous trees break down their chlorophyll as days shorten and temperatures fall. As the green pigment disappears, the yellow and orange carotenoids that were always present but masked by chlorophyll are revealed. Some trees also produce red anthocyanins as they break down leaf sugars. The specific mix of pigments in each species — maple, oak, birch — produces the characteristic autumn display. This is why New England and parts of central Europe are famous autumn tourism destinations.
Real world: Paper chromatography in food science
The same technique used to separate plant pigments — paper chromatography — is used in food science labs to test whether food dyes are genuine and properly labelled. A tiny spot of food colouring is placed on special paper and a solvent is allowed to travel up. Different dye molecules move at different speeds, producing a pattern of coloured dots. This lets inspectors verify that products contain only approved dyes and no undeclared additives.
Real world: Grow lights and the light spectrum
Growers using LED grow lights for indoor plants choose red and blue LEDs specifically because chlorophyll absorbs those wavelengths most efficiently. Green LEDs are largely wasted because chlorophyll reflects green light. Red LEDs (around 660 nm) promote flowering and fruiting; blue LEDs (around 450 nm) support leaf and stem growth. Understanding the absorption spectrum of chlorophyll directly informs which light wavelengths are worth paying for.
Where do you see this in real life? In autumn, look closely at a changing tree. The gradients of green fading to yellow and orange, and red appearing in some species, are all explained by which pigments break down first and which are synthesised as temperatures drop. You can see the result of chlorophyll, carotenoids, and anthocyanins all at work in a single leaf.
Practice Problems
Why do leaves appear green?
Show answer
Explain why leaves change colour in autumn.