Question

The stage when all the body parts can be identified is known as
A. Zygote
B. Foetus
C. Embryo
D. Infant

Answer 1

The first step in the process of sexual reproduction is the process of fusion of a sperm and an ovum. When the sperm comes in contact with an egg, one of the sperm fuses with the egg. Such fusion of the egg and the sperm is called fertilization. Fertilization that takes place inside the body of the female is called internal fertilization.

Complete answer:
In human beings, a single matured egg is being released into the oviduct by one of the ovaries every month. Uterus is the part where the development of the baby occurs.
A zygote is a eukaryotic cell which is formed when an egg cell is fertilized by a sperm cell. The zygote is the earliest developmental stage. Hence, all the body parts cannot be identified in this stage.
A foetus is the unborn offspring that later develops from an embryo. Fetal development takes place from the ninth week after fertilisation and then goes on until birth. A fetus is characterized by the presence of all the major body organs, but they will not be fully developed and functional.
An embryo is considered to be the early stage of development of a multicellular organism. Embryonic development starts just after fertilization and continues through the formation of body structures, like tissues and organs. Each embryo starts developing as a zygote, which is a single cell resulting from the fusion of gametes.
An infant means a very young offspring of human beings. The term is also used to refer to juveniles of other organisms. An infant is only hours, days, or even up to one month old. A newborn or neonate refers to an infant in the first twenty-eight days after birth.

Thus, the correct answer is option B.

Note:
The placenta acts as a maternal-fetal barrier against the transmission of microbes which can cause infections. When this barrier is insufficient, mother-to-child transmission of infectious diseases takes place. A developing fetus is highly susceptible to anomalies during its growth and metabolism, thereby increasing the risk of birth defects.