notes on complete development stages of frog
Answers
When sperm fertilize the egg, streaming movements are set up in the egg and these results in distribution of materials. So that three regions can be seen, the upper animal hemisphere (pole) which is pigmented and lower white vegetal pole. Between the two hemispheres, there is a small are with no pigment called grey crescent.
Explanation:
2-3 hours after fertilization, the zygote begins to divide. The repeated division in the successive fashion is known as cleavage or segmentation.
Division is mitotic
The cleavage begins as a small depression at animal pole and gradually extends surrounding the zygote, dividing into two cell.
The divisions are holoblastic and complete
First cleavage is vertical; two celled stage
Second cleavage is also vertical but right angle to the first one; forms 4 celled stage
The cells are known as blastomere
Third cleavage is horizontal but above the equatorial line forming unequal size cells. The upper 4 cells toward animal pole are small and pigmented known as micromeres or epiblast. The lower 4 large yolk laden cells are known as megameres or hypoblat.
Fourth and fifth cleavage are also vertical forming 16 celled zygote. These division is followed by two horizontal cleacage, one toward animal pole and other toward vegetal pole, resulting in 32 celled stage.
Morula (mulberry shape stage):
As the result of repeated and irregular cleavage, ball of cells is formed known as morula stage.
One hemisphere of morula is composed of large number of small black and yolkless cells known as micromeres and other hemisphere is composed of fewer number of large white and yolk laden cells known as megameres.
Blastula stage:
The micromeres dives more rapidly than megameres which results in formation of small fluid filled cavity known as Blastocoel or segmentation cavity.
Blastocoel bearing stage is called Blastula
The floor of blastocoel is composed of layer of yolk laden megameres while the roof is composed of micromeres.
In this stage early Presumptive areas can be differentiated by staining technique.
The entire animal pole of blastula represents the presumptive ectoderm, which is further divided into presumptive epidermis and presumptive neural plate
A small area near vegetal pole is presumptive notocord
Close to presumptive norocord there is a grey crescent region which is the presumptive mesoderm
The remaining vegetal region is presumptive endoderm
Answer:
It includes three stages: Egg, larva, and adult
The life cycle of a frog consists of three stages: egg, larva, and adult. As the froggrows, it moves through these stages in a process known as metamorphosis.