I listened to a lecture by Richard Dawkins some time ago in which he claimed that all intelligent men must accept that they have descended from turnips. I was surprised to hear Dawkins come right out and say this. Is Dawkins somehow implying that turnips are a lower life form just because they do not belong to his phyla? Then I submit that the opposite is true, that turnips are really superior to the human race, as can easily be shown.
The turnip harvests light energy from the sun and uses this energy to split one of the most stable molecules in existence… water. It accomplishes this tricky and dangerous task with the help of a complex molecular machine called the chloroplast. Even the authors of my biology textbook, who rarely display any emotion, cannot help but raise their beakers with a toast to the chloroplast.
“…the splitting of water is the most thermodynamically challenging reaction known to occur in living organisms. Splitting water in a laboratory requires the use of a strong electric current or temperatures approaching 2000 deg Celsius. Yet a plant cell can accomplish this feat on a snowy mountainside using only the energy of visible light.” 1
By splitting water, the turnip plant takes what it needs from water (the 2H+ ions and 4e-) and releases what is left over… oxygen. And by absorbing CO2 and releasing O2 the turnip does a great service to those of us who need O2 and release CO2. But the turnip plant does much more than scrub the air. It uses the energy harvested from the sun and the carbon absorbed from the air to make turnips!
It is good that the turnip plant makes turnips because human beings have not yet evolved the ability to photosynthesize. We need to get our energy from a different source than the sun and it so happens that a turnip contains a lot of energy… if we can get at it. But reducing a turnip back into usable energy is not easy. It requires another kind of cellular power plant… the mitochondria.
The mitochondria is a close counterpart to the chloroplast and uses a similar series of chemical reactions, except in reverse. Rather than splitting water and releasing oxygen, it uses oxygen to reassemble a molecule of water. In the process it releases CO2. Just as it was tricky for the chloroplast to split water, it is also tricky for the mitochondria to put the water molecule back together again. Here are the authors of my textbook again, now completely hammered,
“A major challenge for investigators is to explain how [oxygen is transformed back into water]. Most importantly, the process must occur very efficiently because the cell is dealing with very dangerous substances; the “accidental” release of partially reduced oxygen species has the potential to damage virtually every macromolecule in the cell.” 2
These two little power plants, the mitochondria and the chloroplast, use each others waste products and final products. One splits water and releases oxygen, the other uses oxygen and re-assembles water. One uses CO2 to create a sugar or starch, the other uses sugar or starch and releases CO2. The complementary nature of the mitochondria and the chloroplast and the way they are both designed to make use of water, carbon and oxygen reveals a hi level of interdependence between turnips and men. It is, perhaps, not fitting to say that one descended from the other lest we slight the humble nobility of the wonderful turnip!
An Ode to the Turnip
with leafy green top
and pale yellow root.
You are very nutritious
although you taste