Differentiate between Foetus and Zygote

A zygote is a single-celled structure formed when a sperm fertilises an egg. It marks the beginning of a new organism and undergoes multiple divisions to develop into an embryo. A foetus, on the other hand, is the stage of development in the womb after the embryonic stage, typically starting from the 9th week of pregnancy. The primary difference is that a zygote is a single cell, while a foetus is a multicellular, more developed stage of the organism.

Complete Answer:

To differentiate between foetus and zygote, it is important to learn the stages of zygote to foetus formation. Here are the different stages:

• Zygote Formation: The zygote is formed when a sperm cell fertilises an egg cell. This single-celled structure contains the complete genetic material (46 chromosomes) required for the organism’s development.
• Cleavage: The zygote undergoes rapid mitotic divisions, forming a multicellular structure called a morula (a solid ball of cells).
• Blastocyst Formation: The morula develops into a hollow structure called the blastocyst, which implants itself into the uterine wall around the 6th day after fertilisation.
• Embryonic Stage: From implantation to the 8th week, the cells differentiate into tissues and organs. This stage is marked by the formation of the heart, brain, and spinal cord.
• Foetal Stage: Beginning from the 9th week of development, the embryo is now called a foetus. During this stage, organs mature, bones develop, and the foetus grows in size until birth.

Differentiate between foetus and zygote:

Here are the key differences between foetus and zygote:

Foetus	Zygote
A foetus is the developmental stage in the womb starting from the 9th week of pregnancy until birth.	A zygote is a single-celled structure formed by the fusion of a sperm and an egg during fertilisation.
It is the final stage of prenatal development, following the embryonic stage.	It is the first stage of development after fertilisation.
A foetus is large and visibly shaped. It resembles a human form with defined features and organs.	A zygote is microscopic and consists of just one cell.
A foetus is a multicellular organism with specialised cells, tissues, and organ systems.	A zygote is a single-celled organism that divides rapidly through mitosis.
In a foetus, there are fully formed organs and systems that are present and continue to grow and mature.	In a zygote, no organs or tissues are formed; it is primarily genetic material preparing for cell division.
A foetus exists from the 9th week of pregnancy until birth (approximately 38–40 weeks of gestation).	A zygote exists for the first 24–30 hours after fertilisation.

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