Death is not an obligate part of such cycles. Differentiation can be defined as display of different phenotypes by cells of the same genotype. Examples range from bacterial spore formation to the formation of different cell types in animal development. Sexual reproduction involves an alternation of haploid and diploid phases, involving fusion of haploid cells to form diploid cells, which can undergo genetic recombination and give rise to haploid cells with new combinations of genes. Germ cells are those that will undergo meiosis to form haploid gametes and give rise to the next generation.
Somatic cells are all the rest.
The germ cells are part of the immortal chain of life that passes from generation to generation. The fate of the somatic cells is aging and death. In a sense, we, the somatic organisms, exist only to nurture and protect our germ cells and to bring them together under circumstances that will allow them to fuse and pass life to the next generation. All but the simplest metazoans begin their development as embryos, formed from fertilized eggs. For all animals, embryonic development shows common features.