Rather than paraphrase an answer from texts, there are a few readable?
excerpts from textbooks to which I will give you links at the end of
this comment.
The problem is that they assume at least a couple of years of college
biology/cell biology.
Basically the short answer they give is that the genes in the cells of
apples are differentially expressed during development and this
determines the shape of all organisms. Unfortunately, these terms
don't mean much without some serious studying.
All cells within the same organism (a fruit tree, an eagle, a
goldfish) have the same set of genes (with the exception of gametes).
What "turns" one cell into a root cell, another cell into a leaf cell,
and another cell into an apple is that some genes within a cell are
activated (turned on and make proteins ) but others are not turned on.
So, for example, that's why hair doesn't grow out of our eyes. Eye
cells have the same genes as skin cells and if those genes were turned
on, eye cells would be able to produce the proteins that make hair,
but those genes are not turned on and so we don't have hairy eyes.
And that same mechanism (differential expression) that turns on and
off given genes based on whether one cell is a root cell and another
is a leaf cell, coupled with feedback from the cell's surroundings
(i.e. cells communicate with one another using chemicals), is what
gives any organism its shape, from apples to starfish to lions.
But notice I do not say precisely why an apple is roughly a round
sphere or a carrot a long tube or how a sea shell has such wonderful
geometric patterns. How do genes encode for specific features and
shapes? How does a cell know that it is part of an eye and not part
of a heart? How does a cell know its supposed to be a leaf? Or
become an apple? And how do tens of thousands of cells communicate
with one another and "know" how to become an roughly spherical apple?
We still do not know for sure *exactly* how. We know some genes are
turned on and off. We know how to turn genes on and off. We know
cells communicate with one another using chemicals. We know that the
concentration of certain chemicals within embryos vary from front to
back, side to side (chemical gradients). But the exact details are
still being discovered. Scientists are still conducting experiments
in the area of developmental biology.
That leaves room for pseudo-scientists and charlatans to say, "Even
scientists can't tell you why an apple is round! So my theory, that
I present to you with *no proof* whatsoever, is obviously right."
A second major disadvantage science always has versus pseudoscience -
science is often difficult to explain. Isaac Asimov (deceased) used
to be brilliant at explaining scientific concepts so that bright kids
(and their parents) could understand difficult concepts.
Unfortunately, I do not have his skills. I hope the links to the
textbooks below will be useful.
----------------------------
I also found a web site that promotes the idea that magnetic fields
give apples their shape.
http://www.championtrees.org/yarrow/newton.htm
Personal opinion - the sheer scientific ignorance of this site is
stunning. For example, modern physicists and theorists do not say
that salmon use anti-gravity to swim upstream past waterfalls.
However, the writing is very readable.
The basic argument from the site is that apples are donut shaped,
magnetic fields are donut shaped, so magnetic fields determine the
shape of apples. (The argument from the web site is slightly more
complicated - plants are antennas, etc, but not by much).
"All apples share a basic shape: curved and circular, but not
like sphere or bubble. Rather, apples are dimpled top and bottom for
stem and sepals to attach. Apples are really donuts without a hole at
center. Instead, apple has five ovaries in its core.
One physical force with this donut shape is magnetism.
...
As flower, seed turns inside out; expanding energy contracts to
condense as fruit whose geometry reveals in compact form this
formative force"
As you can tell, I was not convinced by the brilliant logic given
above.
-----------------------------------------------------------
An introduction as to how the shape of plants is determined.
Molecular Biology of the Cell, 3rd edn.
Part IV. Cells in Their Social Context
Chapter 21. Cellular Mechanisms of Development
Plant Development
Introduction
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?query_key=61&db=books&dopt=&page=0&dispmax=20&WebEnv=0Xe7po9RxNymTWLV2mGxkMxxO3hy_-Oa3R0XpUek1So-e-XYvLZ85X&WebEnvRq=1&rid=cell.section.5697#5714
Plants and animals are separated by about a billion years of
evolutionary history. They have evolved their multicellular
organization independently but using the same initial tool kit - the
set of genes inherited from their common unicellular eucaryotic
ancestor. Most of the contrasts in their developmental strategies
spring from two basic peculiarities of plants. First, they get their
energy from sunlight, not by ingesting other organisms. This dictates
a different body plan. Second, their cells are encased in semirigid
cell walls that are cemented together, preventing them from moving as
animal cells do. This dictates a different set of mechanisms for
shaping the body and different developmental mechanisms to cope with a
changeable environment.
And from the same textbook - what shapes the body plan of animals.
---------------------------------------------------------------------
Molecular Biology of the Cell, 3rd edn.
Part IV. Cells in Their Social Context
Chapter 21. Cellular Mechanisms of Development
Morphogenetic Movements and the Shaping of the Body Plan
Introduction
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?query_key=63&db=Books&dopt=&page=0&dispmax=20&WebEnv=0TNiFq4po53He8Bn8RicKQt_P0p81agM19E48GsSnCPeWc3uBdel5k&WebEnvRq=1&rid=cell.section.5539#5540
------------------------------------------
Developmental Biology, 6th edition,
Vegetative Growth
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?query_key=67&db=Books&dopt=&page=0&dispmax=20&WebEnv=0d9qk2ailcO6M7SbAooBZVqH257iy1KPZIa7Rhh3grnX8cP6tgo55o&WebEnvRq=1&rid=dbio.section.4989 |
