Erin Norriss, of Ilam School, asks :-
James Rogers, at Borough School, asked:-
Why do leaves on some trees change colour in autumn?
Warwick Harris, a botanist at Landcare Research, Lincoln, responded.
We usually see changes of leaf colour from green to yellow, orange, and red as something that happens to trees that lose leaves in winter. These are deciduous trees, and those that have leaves all year round are evergreen. But some evergreen trees have leaves that are never green, and others change from having green leaves in summer to other colours in winter.
Chlorophyll, the green pigment of leaves, traps energy from sunlight. Plants use this energy to combine water and carbon dioxide to make sugars which provide food for the life of all plants and animals.
Pigments that give other colours to leaves, flowers and fruit are complex compounds called carotenoids and flavonoids. We know plants use fruit and flower colours to attract animals to help set and spread seed, but it is not certain why these pigments are formed in leaves.
One idea is that pigments protect leaves from rays in sunlight that damage plant cells. Frosted leaves are especially sensitive to these rays. So it is possible that the autumn and winter leaf colours are screening plants from damaging sun rays during cold times of the year.
Like plants, people also produce pigments to protect their skin from sun rays that can burn and initiate skin cancer. But if we are wise we also put on hats and apply sun screen products to protect ourselves from the dangerous rays of sunshine.