Question

Choose the correct option with respect to the assertion and reason given.

Assertion [A]: Blastocyst burying itself within the uterine wall is known as implantation.

Reason [R]: Zona pellucida prevents the embryo from attaching to the wall of fallopian tube.

• A. [A] is true and [R] is false.
• B. [A] is false and [R] is true .
• C. Both [A] and [R] are true and [R] is a correct explanation to [A].
• D. Both [A] and [R] are true but [R] is not a correct explanation to [A].

Answer 1

The correct option is C

Both [A] and [R] are true and [R] is a correct explanation to [A].

The zona pellucida surrounds the developing embryo during its entire journey down the fallopian tube and prevents the embryo from attaching prematurely to the wall of the fallopian tube. Once the blastocyst reaches the uterus, it uses a protease, to penetrate the zona pellucida. It then squeezes through the hole moving out of the zona pellucida. Proteins on the outer surface of the blastocyst bind to the extracellular matrix of the uterine wall and allow the blastocyst to attach to it. Once attached, the blastocyst secretes a number of different proteases that digest the extracellular matrix of the uterus and allow the blastocyst to bury itself in the uterine wall. This process by which the blastocyst binds to and then buries itself within the uterine wall is known as implantation.