Why are plants green?

It’s summer, the plants are in full sap – the world shines a lush green. This color is almost a symbol for nature, even political parties underline their ecological sentiment with it. But why are plants green at all and not black, white or even purple? In this article we explain why plants are green.

The answer is not that complicated: “It has to do with one of the foundations of life: photosynthesis, through which plants convert light into chemical energy such as sugar”. The color of an object always determines the color of light that it reflects. In the case of plants, it is light with a wavelength of green. “The plants only need the blue and red light for photosynthesis, the green light does not help them and they simply reflect it back,” explains Kleine. That is why plants are green in color.

Pigments with a “green gap”

In this context, one even speaks of the “green gap” – it describes the area between 490 and 620 nanometers of sunlight, which is outside the absorption spectrum of the plants. Specifically, it is the so-called chlorophylls that give plants their green color. With the help of these pigments they can absorb the light energy. They use the leaves like solar cells, which they stretch into the light to generate energy. However, they do not generate electricity, but chemical energy: Plants convert the low-energy compounds carbon dioxide and water into energy-rich substances – the carbohydrates. They also form the basis of human existence, because the energy that we ingest through food was ultimately generated from sunlight by a plant at the beginning of the food chain.

Chlorophyll as a light catcher

The chlorophyll is vital for plants. With this dye, the plant can capture the energy of sunlight and convert it, together with water and carbon dioxide, into glucose. Since this process also creates the oxygen that we need to breathe, plants are vital for us. By the way, this process is called photosynthesis.

The glucose produced by photosynthesis is rich in energy and is transported as fuel to all parts of a plant. There the grape sugar is used to build wood, bark and leaves.

Chlorophyll is green

To understand why the chlorophyll and thus the leaves are green and not blue, for example, one must first know one thing: Sunlight is composed of several colors. You can see that impressively in a rainbow. There the water droplets split the light into its colors.

The green chlorophyll in the green leaf absorbs the red, purple, blue and yellow rays of the sun and uses the energy from this light to photosynthesize. Only the leaf does not need the green color. This color is simply thrown back from the leaf and is the only color that arrives in our eye. That’s why leaves look green!

Rest in winter

Many plants take a break from growing during the cold, dry winter months. In most native deciduous trees, the chlorophyll regresses and is slowly broken down. The leaves on the trees first change color and then fall off.

Why some leaves are colorful anyway

But how is it that some plants do not have green leaves at all, but red ones, such as the copper beeches or some ornamental plants? “These plants are actually green too,” explains Kleine, “the green is only covered by other dyes, the so-called anthocyanins”. Some plants form these red pigments as protection against too strong UV light, similar to how a person gets brown skin. The green chlorophylls are also hidden under this red dress and collect the energy of the sunlight.

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