Given below are diagrams showing the different stages in the process of fertilisation of an egg in the human female reproductive tract. Study the diagrams and answer the questions: Given below are diagrams showing the different stages in the process of fertilisation of an egg in the human female reproductive tract. Study the diagrams and answer the questions:
Arrange the letters given below each diagram in a logical sequence to show the correct order in the process of fertilisation.
Topic: Sequence of fertilisation
Answer
D → C → B → A
(The order C → B → A → D is also accepted by the marking scheme.)
Work out the order from what is HAPPENING in each picture rather than from the letters: several sperms surrounding the ovum, none yet entered one sperm penetrating the membrane the sperm nucleus inside, approaching the ovum nucleus the two nuclei FUSED, forming the zygote
THE BIOLOGY BEHIND THE SEQUENCE: many sperms reach the ovum but only ONE enters. The acrosome of that sperm releases the enzyme HYALURONIDASE, which dissolves the covering of the ovum so it can penetrate. The instant it does, a FERTILISATION MEMBRANE forms around the ovum and blocks every other sperm — which is why the offspring receives exactly one set of paternal chromosomes.
The marking scheme accepts two orders, so describe the stages clearly and the sequence follows.