Test: Fertilisation, Embryonic Development & Parturition - NEET MCQ

• The process of implantation is followed by the rapid differentiation of the inner mass of cells of the blastocyst.
• These cells differentiate into the outer layer of ectoderm and the inner layer of endoderm.
• Mesoderm arises later.

The mesoderm germ layer forms in the embryos of triploblastic animals. During gastrulation, some of the cells migrating inward contribute to the mesoderm, an additional layer between the endoderm and the ectoderm.The formation of a mesoderm leads to the development of a coelom. 

In humans, ovum is released from the ovary in the secondary oocyte stage. The wall of the ovary gets ruptured to release the oocyte. In humans ovulation occurs about 14 days before the onset of the next menstruation. Ovulation is induced by LH.

A single-celled zygote will undergo multiple rounds of cleavage, or cell division, in order to produced a ball of cells, called a blastula, with a fluid-filled cavity in its center, called a blastocoel.

A graafian follicle can be defined structurally as a heterogeneous family of relatively large follicles (0.4 to 23 mm) characterized by a cavity or antrum containing a fluid called follicular fluid or liquor folliculi. The characteristic structural unit of all graafian follicle is the antrum. For this reason, the term antral follicle is used correctly as a synonym for graafian follicle. 

The embryo with 8 to 16 blastomeres is called a morula. Morula is the solid mass of cells and is mulberry like. Morula is a developmental stage between the zygote and blastocyst.

• Ectoderm and endoderm are the first layers that arise as a result of the differentiation of the implanted blastocyst.
• Eventually, a third layer separating ectoderm from the endoderm arises.
• This layer is called mesoderm.

HCG (Human chorionic gonadotropic hormone) is the basis for pregnancy test. It is seen in the urine.

Internal fertilization is a type of fertilization in which there is union of an egg and sperm inside the body of a parent. Examples include reptiles, mammals, birds. Colostrum is the first form of milk that is produced by the mammary glands of mammals. It contains large numbers of IgA antibodies and lymphocytes that help protect the mucous membranes of the infant. Polyspermy is a condition in which egg has been fertilized by more than one sperm. It is prevented by depolarization of the egg plasma membrane after the entry of first sperm. This depolarization prevents the entry of additional sperms. The fertilized ovum enters the uterine cavity 3-4 days later. Implantation occurs almost 7 to 10 days after fertilization and 5 to 6 days after it has entered the uterine cavity.

Thus, the correct answer is 'Polyspermy is prevented by the chemical changes on the egg surface..'

The stem cells are a population of cells within the inner cell mass that possess the ability to give rise to an entire organism. They have a property called stemness, which gives them this ability.