Why are leaves green?

When we look at plants there are many features that might stand out to us such as flowers and bark on trees. One of the most common features in plants is green leaves. But why do so many plants have green leaves? 

All leaves contain a pigment called chlorophyll. A pigment is a type of chemical that gives things their colour. They control the colour of your eyes and the colour of an animal’s fur. 

Chlorophyll is a special type of pigment. It plays an important role in the plant’s survival and also gives it its green colour.

WHAT DOES CHLOROPHYLL DO?

Chlorophyll absorbs light from the sun. It uses the energy from the light to power a process called photosynthesis. 

Photosynthesis is how a plant produces the chemicals it needs to grow and survive. It requires energy, water and a chemical called carbon dioxide. 

Photosynthesis also releases oxygen. Animals and humans need oxygen to survive. When we breath we are taking in oxygen produced from plants from the air surrounding us.

WHY IS CHLOROPHYLL GREEN?

Light from the sun contains all visible colours. The combination of all these colours makes the light appear white. Chlorophyll is able to absorb all of these colours except for green. Green light reflects (bounces off) the leaf. This light is what we see when we look at a leaf, and why it looks green.

WHY ARE SOME PLANTS OTHER COLOURS?

Many plants have colourful flowers. Flowers can be many colours like orchids that can be red, yellow, blue or many other colours. 

The colour of flowers is also decided by the pigment molecules that they contain. Flowers are brightly coloured for a reason – it’s not just to look pretty! Flowers have bright colours to attract bees, birds and insects to them. These creatures pollinate the plants. Pollination is a process which allows plants to reproduce by carrying a substance called pollen between them.

WHY DO LEAVES CHANGE COLOUR?

Some leaves change colour to yellow or brown and fall off trees. When this happens, it means the leaf has died. 

The leaf changes colour because the chlorophyll in the leaf has broken down. This means the plant can no longer photosynthesise to produce the chemicals needed for its survival. 

The yellow or brown colour remaining comes from other pigment molecules that are within the leaf. These pigments do not absorb sunlight as effectively as chlorophyll.

A leaf’s colour can also be used to determine if a plant is diseased or dying. If we can identify this, we can provide the plant with what it needs to recover. For example, Yam leaves may turn yellow or brown if they are not receiving enough water. This is a sign that the plant needs to be watered more.

Marwin Ramos

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