Re: What makes veggies get softer as they cook?

Is does have to do with starch and also with cell walls. However, it is 
important to say that starch IS NOT part of the plant cell wall. Starch is 
inside the cell, while the wall surrounds the cell.
A lot of things happens when you boil the tissue. The cell dies, the 
citoplasm leaks to the water, and a many components solubilizes in the hot 
water. Since you are interested in the consistency of the veggies, let's 
focus on the elements that are important to the texture: the cell wall and 
(to some extent) starch. 
Althought cellulose does not dissolve in hot water, many other wall 
componentes do. Polymers like pectins and hemicellulose (it really does not 
mather what they are exactly) may leak out to the wall under the usual 
cooking conditions. Without these elements, the cell wall simply does not 
work properly: the cellulose changes it's distribuition, the wall gets too 
porous and the cellular content leaks. Part of the starch (called 
amylopectin) solubilizes and the starch grains get "soft".
Together, all these changes make the tissues softer, but, as you can see, 
many elements are involved in the process.
Hugs,
Marco.