Re: Why are seeds alive?

Seeds may seem dry, but they typically contain about 10% water.  Think 
about popcorn.  The conversion of the water into steam in the seed is what 
makes it POP!  It is enough water to kee alive, although not metabolically 
very active.  The uptake of additional water starts the germination 
process, essentially signalling that there is plenty of water available. 

A seed contains an embryo and stored food for the emerging plant, all 
enclosed in a seed coat.  This is a survival mechanism which allowed for 
the dispersal of plants away from the aquatic environment, a major key to 
angiosperm ("fruiting plant") success.  The seed does not have to start a 
new plant immediately, but can wait for suitable conditions.  Germination 
of the seed is the resumption of growth and development which was 
suspended while the seed matured.  The embryo is dormant (hibernating) 
until suitable conditions arrive.  

The conditions which are suitable depend on the plant.  All need 
sufficient water, oxygen, and temperature.  Some may germinate immediately 
if these conditions are met.  Others need a specific environmental cue 
before germinating, such as a period of cold (so a plant will not start in 
November with a long cold period ahead, but will germinate when the spring 
season starts).  Some seeds also need light for germination, ensuring that 
they are close enough to the surface. The manzanita of the California 
chaparral does not germinate until a fire burns through.

The first step in germination is uptake of water which expands the seed 
and ruptures the seed coat.  The uptake of water (called imbibition) also 
activates digestive enzymes which release the food reserves of the seed 
for the embryo, to sustain it until the its photosynthetic capabilities 
can take over.

You can find out more about seeds and germination in a Botany textbook, 
such as   Biology of Plants by Raven, Evert, and Eichhorn.
  
For advanced study, try: Seeds-Physiology of Development and Germination 
by J. Bewley and M. Black.

To find some of the latest research on seeds and germination, search the 
American Society of Plant Physiologists site at: 
http://www.sheridan.com/search