The acorn is an oak acorn. It is the species of it's parents, although it does not demostrate all the characteristics of the seedling, sapling or full grown tree stages of development of the oak. It is not necessary for members of the species to demonstrate all of the characteristics of the species at any one time or even at any time in the life span in order to qualify as a member of the species. For most purposes it is only necessary to be of the species by parentage (usually sufficeint for classification) and/or to demonstrate the appropriate characteristics of that stage.
The embryo utilizes nutrients from the environment in the fallopian tube and in the uterus, even before gastrulation and implantation. (The zygote is appropriate nomenclature only at the one cell stage of the embryo.)
Is an acorn, or an appleseen, or any other type of seed generally considered to be "alive", in common terminology, before it germinates? Prior to germination, it's possible, in the right environment, for a seed to exist without changing or growing for a substantial length of time. Once a seed has germinated, however, it must from thenceforth either grow or perish.
I would liken a plant seed to a gasoline engine with a fuel pump, magneto-based ignition, a weak battery, and no alternator. As built, the motor contains everything necessary for operation except fuel; if fuel is present soon enough after the starter is activated, the motor will be run for a long time. If fuel is not supplied soon enough after starting, or if the fuel supply is ever discontinued, the motor will die and not be restartable. As shipped from the factory, the motor's static state contains everything necessary to allow the motor to operate once given fuel and activated. Once the motor is started, however, the kinetic energy of various parts of the motor becomes an essential part of its operation. If that kinetic energy is removed, even if no physical part of the motor is damaged, the motor will become useless. I would posit that a human zygote/embryo is somewhat similar. Initially upon fertilization, the static state of the embryo holds everything necessary to 'start it up'. Even if one removes the dynamic aspects of its state by freezing it in liquid nitrogen, the static aspects of its state will allow it to restart when it's thawed. Once the embryo has implanted, however, then the dynamic aspects of its state become critical and if they are ever lost, the embryo will die.