Optometry Admission Test (OAT) Practice

What occurs during the implantation stage of embryonic development?

1. The embryo implants during gastrulation

2. The embryo implants during ovulation

3. The embryo implants during blastulation

4. The embryo implants during the fetal stage

The correct answer is: The embryo implants during blastulation

During the implantation stage of embryonic development, the correct process is associated with blastulation. After fertilization, the zygote undergoes cell divisions to form a multicellular structure known as the blastocyst. This blastocyst is what eventually implants into the uterine wall. The implantation occurs when the blastocyst attaches itself to the endometrium, which is the lining of the uterus, marking a critical point in pregnancy as it allows the developing embryo to receive nutrients and support from the mother. This stage is vital for establishing the connection necessary for continued development and growth of the embryo. Other options refer to stages when implantation does not occur. Gastrulation is a later stage where the blastocyst is already implanted and begins to form the three germ layers. Ovulation is the process where an egg is released from the ovary and does not involve implantation at all. The fetal stage is a much later phase after the embryo has fully developed and is no longer in the implantation stage.