What is a key characteristic of totipotent cells?

Totipotent cells are characterized by their ability to differentiate into all possible cell types, including both the embryonic cells that will form the organism itself and the extraembryonic tissues such as the placenta. This unique capability is pivotal during the earliest stages of development, particularly in the context of fertilization and early embryogenesis.

In the context of embryonic development, totipotent cells, such as the zygote and the first few divisions after fertilization, have the potential to develop into a complete organism. This includes contributing to both the inner cell mass that ultimately develops into the embryo and the trophoblast, which becomes part of the placenta. This versatility is what distinguishes totipotent cells from other types of stem cells, such as pluripotent cells, which can give rise to nearly all cell types but cannot form an organism on their own as they cannot develop into extraembryonic tissues.

This understanding underscores why the option noting that totipotent cells can give rise to both the placenta and the embryo accurately captures the essence of their role in development.