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The walls of plant cells

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Understandig the complexity of only the walls of plant cells would certainly lead to the next step, there must be an intelligent creator!

 

<table align="center" border="0" cellspacing="6" width="90%" height="1568"><tbody><tr><td colspan="2" height="8">The walls of plant cells</td> </tr> <tr align="left"> <td colspan="2" valign="top" height="24">by Harm Geert Muller</td> </tr> <tr align="left"> <td colspan="2" valign="top" height="1215"> We developed a mathematical description of the process of growth of a cell wall around a long elongated plant cell. Many of the layered structures known to occur in real cells can be generated with this single mechanism.

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This figure schematically shows how cellulose fibers wind around the cylindrical plant cell, layer upon layer (three layers shown), each layer continually changing the angle of its fibers with respect to the cell axis.

 

Wood is an amazing material, that has performed a key-role in human technology ever since we came out of the trees. Its popularity as a building material stems from a combination of stiffness, toughness and low weight that is amazing for a material this light.

Wood basically consists of the cell walls of dead cells, the space that was formerly occupied by the living protoplasm of the cells now filled with air. The cells from which the wood is formed are extremely elongated, which makes the wood look like a miniaturized bundle of straws. In a growing tree new cells quickly grow to such an elongated shape, and then start to secrete tough materials on their surface that give them their strength.

The cells that make the wood of tree trunks are extreme cases, and all plant cells have walls made of a strong material, just less thick. This distinguishes them from animal cells, in which the living protoplasm is separated from the outside world is just a (soap-bubble like) membrane. The plant cell walls derive their high strength from long fibrous molecules called cellulose, which are embedded in a glue-like substance and are wound around the cell in layers. It is thus a naturally occurring composite.

Cell walls have a layered structure, and in each layer the cellulose fibers all run in the same direction, nicely put down next to each other like the way a piece of rope is wound when you buy it in the store. From layer to layer the direction in which the cellulose fibers are wound around the cell can be different. Sometimes it alternates from layer to layer, in other cells each layer is rotated a bit compared to the one below.

That is about all that is known about the structure of these walls. It is not known if each layer really has its fibers in the same direction over the entire cell wall, or even if the layers do extend over the entire cell, or just part of it. It is not known how the cell decides in which direction to put down the fibers when it is building the wall.

At AMOLF we developed a theory about how a cell could do this, based on fairly simple means (after all, single cells can not be very intelligent!) It is known that the fibers grow by being extended at one of their ends by tiny bodies ('rosettes') floating in the cell membrane. The theory assumes that the direction in which these bodies move (and lay down the fibers) is determined by their number: If there is just a single one the fiber has to wrap around the cell like the thread of a screw, but if the whole circumference of the cell is crammed with rosettes, they have no room to move anywhere but straight along the axis.

The exact result then is controlled by how rosettes are inserted and retired from the membrane, and the assumption that the insertion occurs in 'waves' that ripple along the cell can explain many of the patterns of cell walls found in nature. The exact pattern one gets is determined by some simple parameters, like the length and repetition frequencies of the waves.<back to main> <back to top>

Protoplasm

The contents of a living cell is known as protoplasm. In very simple organisms like bacteria it is an unstructured fluid in which all molecules needed to sustain life just float around and randomly bump into each other to do their thing (which, in the end, leads to production of more protoplasm). Cells of higher organisms, such as animals or plants, are so large that they have to be highly organized to run their business, and to this end have all kind of specialized compartments. The cell nucleus, containing the genetic material (the DNA 'master tape'), is the best known of these so called 'organelles'.<back to main> <back to top>

Cellulose

A cellulose molecule is a nearly endless repetition of sugar molecules, all chained together. This chaining can be done in two different ways; one way of doing it produces cellulose, the other starch. Almost any living organism can digest starch, i.e. split the chain back into sugar molecules. Only few organisms can break down cellulose; humans have to rely on cooking their vegetables to break open the cell walls and get at the nourishing stuff inside it, and cows rely on certain microbes living in their stomachs. It seems unbelievable, but if you cook wood long enough in acid, you will get sugar (amongst a lot of other crap, so don't try to eat it!)

All plant cell walls are based on cellulose fibers; the material in which the cellulose is embedded can vary. Cells in wood uses the very tough substance lignin, but softer plant parts use other materials.<back to main> <back to top>

Composite

Composite materials consist of fibers of very rigid and strong material, embedded in soft glue-like stuff (called the matrix). A popular man-made composite is glass-fiber reinforced polyester, and the space-shuttle is made of carbon-fiber reinforced carbon.

A very stiff material, such as glass, is superb at resisting deformation, but shatters in a catastrophic way when overloaded. Soft materials, like chewing gum, do not break when overloaded but just flow into a different shape. The reason that glass breaks so easily is that at the tip of a crack the strong material acts as a lever to enhance the stress on the still intact material, overloading that as well and making the crack grow. (Tearing a piece of paper in two uses the same principle.)

Composites are nice because a crack in the hard material can not propagate very far before it reaches the end of the fiber (which is then broken). The soft material around it 'smothers' the stress, by flowing in such a way that is distributes the stress around the break in one fiber over a large part of the neighboring fibers, rather than concentrating it. This way composites can be tough (able to sustain a lot of damage) as well as stiff.<back to main> <back to top>

Illustration by Bela M. Mulder

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Understandig the complexity of only the walls of plant cells wouldcertainly lead to the next step, there must be an intelligent creator!

 

 

Yes indeed. The cosmos is filled with these complexities and complexity is the reason that finally won over the world's leading atheist, Antony Flew, to embrace theism. He wrote a book published last year entitled 'There Is a God',

http://www.harpercollins.com/books/9780061548673/There_Is_a_God/index.aspx

 

For one with eyes wide open the proof of God is literally everywhere before us. For those who refuse to open there eyes no proof can be seen.

 

Flew is rare. He campaigned his whole adult life against the acceptance of a God only to won over at last by the complexity argument. Actually it was the grace of Supersoul that allowed him to see Him at last through the complexity argument.

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Getting a solid glimpse of Krishna's creative shakti in the universe must stun us as it did Arjuna and inspire awe and reverence.

 

Of course one who has established a relationship with Krishna of friendship may not be overwhelmed by awe and reverence and instead simply feel emmense pride in his friend Krishna for being so clever.

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