Question

Describe in detail the development changes of frog? 

Answer 1

The development of frog consists of following four processes: -

Cleavage: -

i) 1st Cleavage: After a period of 2-3 hours the fertilized egg starts dividing into two cells. Each cell is called blastomere.

ii) 2nd Cleavage: It takes place after 1 hour of 1st cleavage. It give rise to 4 blastomere.

iii) 3rd Cleavage: - It starts after half an hour slightly above the equator.

The embryo has now 8 blastomere.

iv) 4th Cleavage: - It starts after 20 minutes and divides the cell vertically.

 This cleavage or segmentation results in the formation of a solid ball of cells which is called morula.

Blastulation: -

i) A series of changes starts after the formation of morula that leads to Blastulation.

ii) A cavity appears in upper half, called bastocoel. 

iii) The embryo at this stage is called blastula and is a hollow ball of cells.

Now the cells move to occupy their new position according to the function.

Gastrulation: -

i) The smaller pigmented cells spread over the large yold cells, except a small circular area called yolk plug. This is the area where a circular depression called blastopore starts appearing.

ii) The cell along the margin of the blastpore move inward to form germinal layers i.e. mesoderm, ectoderm and endoderm.

iii) A cavity called archenteron appears, enlarges and becomes lined with the endoderm.

iv) At this stage the embryo is called gastrula and all these changes collectively called Gastrulation.

Neurula: -

i) The dorsal ectoderm differentiates into neural tube to form nervous system, through a process called neurulation.

ii) At this stage, embryo becomes elongated, develops celia, swims freely and is called Neurula.

iii) Rapid changes occur in the different cellular layers to form different organs of body that converts the embryo in tadpole.

iv) Tadpole is fish like in shape having external gills and long tail.

v) Tadpole larva consumes the food stored in the form of yolk.

vi) After many rapid changes tadpole changes into tailless adult frog.

vii) The process involving changes that transform larva into adult is known as metamorphosis.

viii) The average duration of development is 70-90 days.