According to the SRD:
A deity has one salient divine ability for each divine rank the deity has, plus additional salient divine abilities reflecting its status: Demigods receive one bonus ability, lesser deities receive two bonus abilities, intermediate deities receive three, and greater deities receive five.
Only if Life and Death is amongst the list of salient divine abilities, the deity can use this ability. In order for this ability to be amongst the salient abilities list, the deity must be of rank 6 or higher and Gift of Life or Hand of Death must also be amongst the salient abilities as well.
Suggested Portfolio elements are what the name implies: suggestions. Quoting:
The information is provided as guidance and should not be taken as a rule.
Note that Death portfolio is NOT needed to use the Life and Death ability; but its presence would make the ability more potent (the deity would not need to rest after using the ability).