IGCSE Biology Paper-1: Specimen Questions with Answers 142 - 142 of 208

Question 142



The diagram shows a fetus attached by the placenta to the uterus wall of the mother.

Structure of Uterus Wall

Which of the following matched pair is Incorrect?


Choice (4)


Umbilical cord






Uterus wall




Structure of Uterus Wall
  • The outer cells of inner cell mass, close to trophoblast, differentiate into Amnion. The amnion secretes amniotic fluid which later acts as a shock absorber and prevents the embryo from mechanical injury and dehydration.
  • The trophoblast now differentiates into Chorion (another extra embryonic membrane, after amnion) . The chorion develops chorionic villi which penetrate uterine tissue and later branch to fuse with maternal tissue. The structure formed jointly by foetal tissue and maternal tissue is called Placenta. Later, during embryonic development, the Allantois (another extra embryonic membrane) arises as an outgrowth from the posterior part of gut, and its membrane gets fused with the chorionic membrane to form the Allantochorion membrane. Due to the participation of allantois with chorion, the placenta in human is called Allantochorion placenta. The chorionic villi penetrate deep into blood vessel of uterus and since, they come in direct contact of blood, the placenta in human is also known as Hemochorial placenta.
  • After differentiation of ectoderm from outer part of inner cell mass and endoderm from inner part of inner cell mass, and the mesoderm, between the two layers; the structure becomes triploblastic (3- layered) . All body structures develop from these three germ layers.