Biology Reference
In-Depth Information
FIGURE 22.1
Growth and proliferation during development. Growth is commonly achieved through cell
proliferation, particularly in the development of 'higher' animals. The two processes do not have to be linked,
however, as cleavage can take place without growth, as it does in embryos, growth can take place with no cell
division, and growth of the whole embryo can take place by fluid uptake with no change in cell volume.
Mechanisms of cell expansion, particularly the anisotropic expansion that is so important
in plant morphogenesis, have been discussed in Chapter 6. For this reason, this section of the
topic will focus mainly on the role of cell proliferation in driving tissue growth and on
the role of cell death in limiting the size of cell populations. This chapter will introduce
the control of cell proliferation itself. Chapter 23 will discuss how spatial control of cell divi-
sion can be used to drive morphogenesis directly, while Chapter 24 will discuss the role of
cell death in morphogenesis.
FIGURE 22.2
The size regulation system of organs can compensate for changes in either cell size (volume) or
cell number by altering the other one, in order to achieve a set final organ size. In this diagram, cell volume is
expressed in an arbitrary scale in which 1.0 happens to be 1/20 final organ volume.
