Re: Why is the algal part of lichen considered alive, while mitochondria isn't?

Hi Roopa,

 Thanks for your question. The difference between the two situations you 
described it that the lichen represents a form of symbiosis called 
mutualism where both organisms benefit from the interaction. With respect 
to the algae you studied, this association represents an *obligate* 
mutualistic relationship, since the algae cannot reproduce without the 
interaction. Mitochondria actually form part of individual cells; they're 
not a species that could on its own form a symbiosis with another 
species. The cell has been designated 'the fundamental unit of life,' so 
a part of the cellular machinery wouldn't generally be considered 'alive'.

Hope this helps,
Chris Reigstad