Monday, July 30, 2012
Every autumn across the Northern Hemisphere, diminishing daylight hours and falling temperatures induce trees to prepare for winter. In these preparations, they shed billions of tons of leaves. In certain regions, the shedding of leaves is preceded by a spectacular color show. Formerly green leaves turn to brilliant shades of yellow, orange, and red. These color changes are the result of transformations in leaf pigments.
The green pigment in leaves is chlorophyll. Chlorophyll absorbs red and blue light from the sunlight that falls on leaves. Therefore, the light reflected by the leaves is diminished in red and blue and appears green. The molecules of chlorophyll are large. They are not soluble in the aqueous solution that fills plant cells. Instead, they are attached to the membranes of disc-like structures, called chloroplasts, inside the cells. Chloroplasts are the site of photosynthesis, the process in which light energy is converted to chemical energy. In chloroplasts, the light absorbed by chlorophyll supplies the energy used by plants to transform carbon dioxide and water into oxygen and carbohydrates.
In this endothermic transformation, the energy of the light absorbed by chlorophyll is converted into chemical energy stored in carbohydrates (sugars and starches). This chemical energy drives the biochemical reactions that cause plants to grow, flower, and produce seed.
Chlorophyll is not a very stable compound; bright sunlight causes it to decompose. To maintain the amount of chlorophyll in their leaves, plants continuously synthesize it. The synthesis of chlorophyll in plants requires sunlight and warm temperatures. Therefore, during summer chlorophyll is continuously broken down and regenerated in the leaves of trees.
There is a part of me sure I am misplaced here on the planet. There's another part of me sure I am in a direct line of descent from the very first living thing that led to the current line of descent. It is one of the advantages of accepting evolution, to understand that fundamental connection, unbroken because it has to be, with every form of dna based life on the planet absolutely and unequivocally related one to the other. It cannot be otherwise...well. Perhaps there are five ancestors, five lines of descent, but the incredible sameness of dna coding suggests only one. All the others and they may have been myriad seem to have all died out. Of course the division of life into plants and animals is breathtakingly ancient. Among other things it marked the divergence of the usage of magnesium in chlorophyll (photosynthesis and self sufficiency but generic absence of all motion but simple tropisms) and the usage of iron in hemoglobin (efficient oxygen transport and varieties of motive strategies, but generic absence of true self sufficiency). Self sufficiency means taking sunlight and totally raw materials to form food. Its loss means relying on other living things such as plants and other animals as food sources.
Plants know more than me,
More than you too. They love green
More than anything.
First plants are tiny,
Still tiny after aeons
And birthing giants.
First plants know the way.
Low murmurings from first plants
Tell my ancestry.
Written November 24, 2008
Last saved 7:25 AM on that day
First published February 23, 2009