Harvesting light was the breakthrough, nothing we have achieved since
can compare to the green miracle, the transformation of sunbeams
into carbohydrates. . . from my poem ‘Past & Future’
We owe our life to leaves. When bacteria first harnessed the sun’s energy in photosynthesis oxygen was a byproduct. Released in tiny amounts by untold numbers of bacteria over billions of years, oxygen levels gradually built up in the atmosphere.
A textbook leaf has an upper and lower epidermis, coated with a waxy hydrophobic cuticle protecting the mesophyll vertical palisade cells packed with chloroplasts that power photosynthesis, with more loosely packed cells through which water and gases diffuse between the plant tissues and the surrounding air. Stomata open or close according to the weather and the availability of water and a vascular system connects them to the stem and ultimately the roots, cycles water, waste and nutrients.
But leaves ain’t leaves – there are enourmous variations in colour, shape size distribution and life cycles (evergreen/deciduous) why/ And why are the outermost layers of cells mostly colourless and unable to photosynthesise? You find out in Steven Vogel’s ‘The Life of a Leaf’, Chicago, 2012.
Even just colour variations are astonishing: