We have seen tree leaves many times, but we seldom think about how complex they are.
Highly complex leaf chemistry uses sunlight and common chemicals to make complex compounds that allow the tree to grow. The physical makeup and shape of leaves are also carefully engineered. Leaves are arranged on the tree so that there is an efficient interception of the Sun’s rays. Stand under a tree on a sunny day, and you can see by its shadow that the leaves are wasting very little sunlight.
Tree leaves also have to endure physical abuse. Leaf stems must resist bending vertically to catch the sunlight. At the same time, they must be able to twist or bend horizontally reducing wind drag to prevent toppling the tree. That means the shape of the leaf and stem are critical. Leaf stems are designed to allow the leaf to twist in the wind with little torsional stiffness. At the same time, the stems provide stiffness against vertical flexing which would reduce sunlight exposure. Leaves can also roll-up or take on a cone-shape in the wind to reduce resistance. Sometimes groups of leaves can also fold into a communal cone, to minimize drag.
There are many engineering problems involved in catching maximum sunlight, having enough surface to carry on photosynthesis, and avoiding enough surface area to allow the wind to push the tree over. Tree leaves are another example of the design of living things by a Master Engineer.
© Roland Earnst
Picture Credit: © bigstockphoto.com/jadimages