Exercise 08
To study the blastula stage of embryonic development in mammals, with the help of permanent slide, chart, model or photograph
To study the blastula stage of embryonic development in mammals, with the help of permanent slide, chart, model or photograph
Principle: The zygote undergoes a few cycles of mitotic divisions to form a solid ball of cells called morula. The cells continue to divide and at a later stage a cavity is formed within it. This stage is blastula. The internal structural details of blastula can be observed in its transverse section.
Requirement: Permanent slide, chart/model of T.S. of blastula, compound microscope, lens cleaning fluid and paper.
Procedure:
Observe the slide under lower magnification of the microscope. In case of chart/models/photographs, note the feature of blastula in your practical record and draw labelled diagram.
Observation:
In transverse section, the blastula appears as a sphere with a cavity, called blastocoel within it (Fig. 8.1). Notice an outer layer of blastomeres called trophoblasts. A cellular mass, adhered to the trophoblast is present on one end of the blastula. It is called inner cell mass.
Questions:
What are the differences between blastula and morula?
What are the main structures you observe in T.S. blastula?
Match the stages in column I with features in column II
Column I | Column II |
|---|---|
(a) Trophoblast | (i) Dividing cells of the morula |
(b) Morula | (ii) Outer layer of blastula |
(c) Blastocoel | (iii) Solid ball of cells |
(iv) Cavity |