Joshua Rule, of Ardgowan School, asks :-

How do apples change from green to red?

Carolyn Lister, a biochemist at Crop and Food Research, Lincoln, responded.

The green colour of apples is due to a pigment called chlorophyll. Chlorophyll is also present in leaves and helps the plant convert sunlight into energy so it can grow.

As an apple ripens the chlorophyll starts to break down and the green colour disappears. At the same time the fruit makes another group of pigments, called anthocyanins, which are red. The apple needs light to produce the red colour and if you place a bag over an apple on the tree it will stay green.

In some apples, such as Gala, only some of the cells can produce the red pigments and they end up with little red stripes all over them. Other varieties of apples, such as Granny Smith, do not produce red pigments at all and they stay green because the chlorophyll is much slower to break down.

In Golden Delicious apples the chlorophyll does break down and they turn yellow, because of another group of pigments called carotenoids. This also happens in the leaves of many trees in autumn.

Bright colours attract animals and birds to eat fruit and disperse the seeds. The red pigment is produced only when the fruit ripens and the seeds are developed properly and are able to grow. Humans and animals also get nutritional benefits from eating apples. The pigments in apples are antioxidants and if we eat them they may help protect us from cancer and other diseases. There may be some truth to the old saying "an apple a day keeps the doctor away".