Leaves

Fall (or autumn if you prefer) has been here for quite some time already, and with it the changing of the leaves.  I realized that I don't actually know why the leaves on some trees change colours, though I felt like I should.

Most people can remember from school that leaves have their green colour because of chlorophyll which is used for photosynthesis.  However as summer ends the days begin to get shorter, so the trees don't have as much sunlight and they begin to start storing more nutrients in their roots.  As the chlorophyll leaves the leaves (hah) other pigments (yellow, orange, red) become much more prominent.

The yellow colours of leaves are always there, however they're normally overpowered by the green chlorophyll in the summer.  It's only when the chlorophyll is receding that the yellow colours start to become visible on the leaves.  So yellow is always there, but what about red?  Well not all trees produce red leaves, and the weather can have an effect on their brightness.

It turns out that some trees are able to tolerate direct sunlight better than others.  When nutrients are being transferred away from the leaves the trees are more susceptible to sunlight.  The red pigments in leaves help to protect the leaves and give the trees more time to absorb nutrients.