Why do leaves change colour in the fall?
Answer Leaves change colour due to biochemical processes within them that are triggered by diminishing amounts of daylight, longer nights, and weather factors. Leaves contain three types of natural substances called pigments which determine leaf colour both during the growing season and in the fall. Chlorophyll is the dominant pigment in most leaves and it gives them their green colour in spring and summer. As autumn approaches and the nights get longer, chlorophyll disappears revealing the pigments called carotenoids which give some leaves their yellow, orange, and brown fall colours. In some species, such as the red and sugar maples, bright sunny days and lower evening temperatures combine to cause an excess of sugars produced in the leaves which then create a red pigment called anthocyanin, turning these leaves striking shades of red and purple.
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