Re: advantages and disadvantages of the multicellular state

Dear Tracy,

A general biology textbook will offer you a lot of information and 
examples of unicellular and muiltcellular organims. For your question, I 
consulted "Biology," by Helena Curtis and N. Sue Barnes and here's what 
they have to say about the subject:

The first unicellular cells were distinguished by three different criteria: 
1) the capacity to replicate itself, generation after generation; 2) the 
presences of complex proteins that are essential for chemical reactions on 
which life depends; 3) a membrane that separates the cell from its 
surrounding environment and enables it to maintain a distinct chemical 
identity. The first appearance of multicellular organisms in the fossil 
records was approximately 750 million years ago. The major groups of 
multicellular organism - such as fungi, the plants, and the animals  - are 
thought to have evolved from different types of unicellular organisms. The 
cells of multicellular organisms differ from single cell organisms in that 
each cell type is speacialized to carry out a relative limited function in 
the life of the organism. 
 

Let's compare the differences between  unicellular and multicellular 
organisms. Algae is a good example of an organism that have familiy members 
that are either unicellular or exists multicellular algae. Unicellular 
algae are adapted to living in shallow waters and along the shores. 
Here the waters are usually rich in nutrients, washed down from the land or 
swept up in the currents from deeper water.Each cell is a totally self-
sufficient individual, dependent only on light from the sun and carbon 
dioxide and minerals from the water surrounding it. These cells do not have 
to work hard to receive nourishment since they are constantly being bathed 
in nutrients all hours of the day.  

Multicellular algaea live in a very different environment compared to the 
unicellular algae.The multicellular algae are found in shallow waters and 
along the shores. Thus, they are subjected to huge changes in the 
environment such as the salt concetration, humidity, temperature, light as 
well as abrasive pounding of the surf and the abrasive action of the sand. 
In order to live, the mulitcellular algae have developed mechanisms and 
specialized cells that help it survive such harsh conditions. In other 
words, the multicellular algae has  an advantage by its the ability to 
adapt to its environment.  The specialized cells will have directed 
functions that may make proteins  or establish defense mechanisms that help  
protect the cell from the outside world.  The unicellular organism, who 
lives in a fairly calm and less harsh environment does not have to work 
hard for nutrients. However, it  does not have the ability to adapt to its 
environment quickly and it's inability to adapt may result in danage or 
death to the cell. 

If you are interested in reading more about unicellular and/or  
multicellular organisms, please consult a basic biology textbook.

Have fun with science!
Elsa