Tag: oviparous and viviparous

In amphibians, the metamorphosis of tadpoles occurs after a variable period of from one or two weeks upto several years, depending upon species. The process involves numerous physiological and morphological changes. Thyroxine hormone produced by thyroid gland plays a very important role in the metamorphosis of frog. 

• Complete metamorphosis consists of four stages i.e. egg, larva, pupa and adult.
• Incomplete metamorphosis consists of three stages i.e. egg, nymph and adult.
• Examples of organisms having incomplete metamorphosis in their life cycle are termites, praying mantis and cockroaches.

Metabolism is the sum of the physical and chemical processes in an organism by which its material substance is produced, maintained,
and destroyed, and by which energy is made available.
Metamorphosis is a profound change in form from one stage to the next in the
life history of an organism, as from the caterpillar to the pupa and from the pupa to the adult butterfly.
Metastasis the transference of disease-producing organisms to other parts of the body by way of the blood or lymphatic vessels or membranous surfaces Morphology is the branch of biology dealing with the form and structure of organisms

• Complete metamorphosis consists of four stages i.e. egg, larva, pupa and adult. 
• Incomplete metamorphosis consists of three stages i.e. egg, nymph and adult.
• Complete metamorphosis occurs in wasps, ants and butterflies while incomplete metamorphosis occurs in termites, praying mantis and cockroaches.

Moulting is the process of casting off the dead rigid outer covering or the exoskeleton or skin of the animal body during its growth. The young larvae casts off its skin in order to allow the growth of the larvae to from the adult. This process is also known as ecdysis.

Extraembryonic membranes are formed outside the embryo from the trophoblast only in amniotes (reptiles, birds and mammals) and perform specific functions.

Periblastula is the blastula of a centrolecithal egg, which is formed by superficial segmentation. This kind blastula occurs in insects.
Centrolecithal eggs develop to superficial blastula, which consists of a single layer of epithelial cells surrounding the centrally placed yolk and there is no blastocoele.
Thus, the correct answer is option (B).

• Metamorphosis refers to the way that organisms develop, grow, and change form.
  
• Metamorphosis majorly occurs in insects.
• metamorphosis has four stages i.e egg, larva, pupa and adult. The female lays eggs then the larva hatch from the eggs. Then the larva makes cocoons around themselves this stage is called a pupa. Inside the cocoon, the larvae change into the adult.
• Hence Changes that convert larva into adult constitute metamorphosis

Tadpole is one of the developmental stages in the life cycle of frogs. The larvae are free-swimming forms which are found in the water. The larvae get metamorphosed to form the adult frog. The thyroid hormones are required for the control and regulation of the events which take place during metamorphosis. 

Thyroxine, the principal hormone, of thyroid gland, is required for tissue differentiation and metamorphosis (the rapid transformation from the larval to the adult form) in amphibians. So in the presence of antithyroid substance, (that inhibits the synthesis of thyroid hormone) e.g., thiourea, tadpoles remain in the larval stage indefinitely. Thiourea is an organic compound of carbon, nitrogen, sulphur and hydrogen. It is similar to urea, except that oxygen atom is replaced by a sulphur atom.