" Given below is the diagram of a human ovum surrounded by a few sperms. Observe the diagram and answer the following questions: (a) Compare the fate of sperms shown in the diagram. (b) What is the role of zona pellucid in this process? (c) Analyze the changes occurring in the ovum during the process. (d) How is the entry of sperm into the ovum facilitated? (e) Specify the region of female reproductive system where the event represented in the diagram takes place. "
class 12th CBSE Biology sample paper
Answers
The diagram is of "a sperm is fusing an ovum" while the other sperm are blocked by zona pellucida membrane of ovum.
(a) The sperm which fuses ovum first will ferilise the ovum and rest of sperm will eventually degrade after some time.
(b)The Zona pellucida ensures the entry of only one sperm into the ovum.
The zona pellucida (ZP) is an important, integral structure for the egg both before and after fertilization.
The ZP is formed by protective secretions that come from the early egg, or oocyte, and 'helper' cells called follicle cells that surround the oocyte at its earliest stage. You can see it around the egg as a thick clear line surrounded by the other cells.
(c) Induces completion of meiotic division of the secondary oocyte, formation of second polar body and a haploid ovum.
(d)The entry of sperm is facillated by the Acrosomes into oovum
The acrosome is a vesicle positioned close to the plasma membrane at the tip of the sperm's head. This vesicle contains soluble proteolytic enzymes (depicted in the diagram as pink contents) and inner membrane proteins, such as bindin (depicted as cyan-colored dots). The nucleus (depicted in green) contains the genetic material that the sperm is trying to pass on, a haploid genome because it contains only one copy of each chromosome.
(e)Region of female reproductive track where fertilization take place is Ampullary - isthmic junction of the fallopian tube