It’s funny how Autumn comes around every year and I realise
how much I love this time of year.... it’s as though I seem to forget I like it
all throughout the other seasons. Of
course we have had a particularly nice Autumn this year in the West of Ireland
and maybe that has re-enforced my happy memories of the season. The days have been bright and crisp showing
off all the beautiful colours in all their glory and splendour.
I grew up in Co. Wicklow surrounded by some beautiful
deciduous woods and forests and this Autumn has really brought my childhood
memories flooding back. My mother
brought us often to the woods as children and we would hunt around for hidden
treasures and delights to bring home and turn into some “masterful” collage in
homage to the season. There was also the
foraging, a distinctive primordial instinct in us all, there is nothing as
pleasing as returning home with your bounty... be it blackberries or sweet
horse chestnuts- to be turned into jams and tarts or painstakingly peeled of
all nasty layers to reveal the divinely
sweet, fruity, nutty delight beneath. In
fact the joy that came with eating the nut always made it suddenly worth your
while to start the arduous task of peeling all over again!
...and I hope that I will never outgrow the delight of
running, kicking, shuffling through a crisp new crop of fallen leaves!
But did you ever wonder about the science behind those
wonderful colours? I did... why the green
suddenly disappears, where does it go and how do the other colours get there in
its place? So, if like me, you ever wondered about these things... here is some
insight into the why and what of Autumn!
As many people know, the lovely green of most leaves is caused
by the pigment chlorophyll... green in colour (obviously) and capable of using
sunlight to convert water and carbon dioxide into energy (sugar) for the plant. However, when the sunlight hours fade coming
into winter so too does the chlorophyll in the leaves of trees, or, to be more
precise, the pigment begins to degrade and is not replaced. Once the green colour is gone other pigments
that are often present in the leaf come into view... carotenoids are pigments
responsible for the yellow/orange colour of leaves, anthocyanins are
responsible for the redder colour of leaves and tannins are responsible for the
brown colour of leaves. There is, within
this pigmented system, a sense of hierarchy, at least in part.
Carotenoids are the pigments responsible for the orange colour of carrots. If carotenoids are present their colour tends
to dominate leaving the leaves yellowy and orange.
In the absence of carotenoid, anthocyanin is the dominant pigment. Anthocyanin (the same pigment found in red
onions, red grapes, red apples and red cabbage) is a natural pH indicator,
meaning that it can change colour depending on the levels of acids or
bases/alkali in its environment. In fact
one of my favourite experiments that I often do with children is to demonstrate
this colour changing using anthocyanin extracted from red cabbage (but that’s a
whole other blog in itself). Anyway, at
the beginning of Autumn the levels of sugar in the leaves tends to be quite
high, increasing the acid levels in the leaves, this strengthens the red colour
of Anthocyanin if it is present in the leaves.
At the end of Autumn the leaves die off and the levels of carotenoids
and anthocynins die off too, leaving another pigment to dominate... and this is
the brown pigment of tannin!
So there you have it... next time you are crunching through
those leaves you may wonder why you are suddenly thinking of carrots and cabbages
and cups of tea!!!
Labels: anthocyanin, autumn, brown, carbon dioxide, chlorophyl, colour, energy, green, indicator, leaves, nature, orange, pH, photosynthesis, pigments, red, science, sunlight, tannins, yellow
