Metamorphosis in Frogs and Insects - Class VIII

Metamorphosis includes the developmental changes during the life span of an organism. The thyroxine hormone released from the thyroid gland brings the developmental changes during the metamorphosis. Thyroxine regulates the metabolism of an organism.

a) Paurometabolous metamorphosis is characterized by gradual development from the immature stage i.e nymph to the adult stage. Eg- grasshopper.

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Caterpillar is the common name for the larvae of members of the order Lepidoptera (the insect order comprising butterflies and moths). A maggot is the larva of a fly (order Diptera). 

The nervous system undergoes least changes during metamorphosis of frog's tadpole. Frog's nervous system once differentiated remains as such throughout life. However, the brain acquires its normal shape and size. 

In each stage of complete metamorphosis, the animal looks different than at all other stages. This is different from incomplete metamorphosis where the early stages of development look like tiny versions of the adult. Butterflies are an example of an insect that goes through all the stages of complete metamorphosis.

Xenopus laevis tadpoles that arrest development and remain as larvae for several years sometimes occur spontaneously in laboratory populations. These tadpoles cease development at an early hindlimb stage, but continue to grow and develop into grossly deformed giants. Giant tadpoles lack thyroid glands, and differ in morphology and behaviour from normal larvae. Tadpoles of frog can be made to grow as giant sized tadpoles, if they are administered large amounts of thryoxine.

• Typically, insects including butterflies have 4 stages in their life cycle.
• The first stage is egg. when the eggs hatch the new insect is called a larva (second stage).
• The third stage i.e. pupa represents the transition between larva and adult ( fourth stage).

The larva is that stage in metamorphosis following which the adult stage is reached. The larvae consume a lot of food in order to fuel their transition into the adult form. Hence, during the larva stage the creature eats a lot of food which acts as the source of nutrition and energy, required for its transformation into an adult.

• Amphibian metamorphosis depends upon the amount of iodine secured by larvae; the greater the quantity the more rapid the differentiation.
  
• Also, thyroxine initiates the numerous morphological and biochemical components of amphibian metabolism.
  

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.

• 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. 

The remarkable axolotl or Ambystoma mexicanum is part of the family of 'mole salamanders', but exhibits an unusual and extreme trait known as neoteny, or paedomorphosis. This is the retention of larval stage characteristics throughout life, so axolotls usually never fully resemble an adult salamander. It is a urochordate.

So, the correct option is ‘i and ii correct’.

• Morphogenesis is the process of the development of shape and structure of an organism when they get mature.
  
• Epimorphosis is the development of the cells and tissues through the dedifferentiation of adult or pre-existing cells. Here the tissues and organs that are lost are replaced by the existing ones. The new organs are originated according to the shape and size required and are also dependent upon surrounding factors.
• Morphallaxis is the formation of tissues and organ due to loss or transformation of an existing organ.
  

A. Cell necrosis - is a form of cell injury which results in the premature death of cells in living tissue by autolysis.

 B. Pinocytic activity - is a mode of endocytosis in which small particles suspended in extracellular fluid are brought into the cell through an invagination of the cell membrane, resulting in a suspension of the particles within a small vesicle

C. Programmed cell death is the death of a cell in any form, mediated by an intracellular program. PCD is carried out in a biological process, which usually confers advantage during an organism's life-cycle.

D. Cell senescence- is a phenomenon by which normal cells cease to divide

So, the correct option is ‘Programmed
cell death’.

Gudernatsch discovered that metamorphosis in frog's tadpole begins only when adequate amount of thyroxine is secreted by the thyroid of the tadpole. It was also found that hyposecretion of thyroxine retards and hypersecretion enhances the rate of metamorphosis. In the hilly tracts of North America from whose soil all iodine has been washed away by rainwater, the tadpoles of Ambystoma probably never metamorphose. Therefore, these tadpoles grow to a large size and attain sexual maturity,i.e., these become paedogenetic larvae. This phenomenon is called paedogenesis. The paedogenetic larvae of Ambystoma are called Axolotl larvae. Addition of thyroxine or iodine in pond water naturally induces and enhances metamorphosis in the tadpoles.

Metamorphosis is the process of transformation from an immature form to an adult form in two or more distinct stages. metamorphosis generally takes place in insects or amphibians and some molluscs, crustaceans, cnidarians, echinoderms and tunicates.
Metamorphosis is seen in frogs which are developed form of the larval stage called the tadpoles. Also, metamorphosis is seen in insects where the adult forms develop from the larva and which also includes the pupal or resting stages as in silkworms.
So, the correct answer is option D.

A tadpole (also called a pollywog) is the larval stage in the life cycle of an amphibian, particularly that of a frog or toad. They are usually wholly aquatic, though some species have tadpoles that are terrestrial. When first hatched from the egg they have a more or less globular body, a laterally compressed tail and internal or external gills. As they grow they undergo metamorphosis, during which process they grow limbs, develop lungs and reabsorb the tail. Most tadpoles are herbivorous. 

Metamorphosis is the sequential developmental stages which are characterized by the process of cell division, differentiation, and maturation. It includes morphological and genetical changes.

Incomplete metamorphosis involves three stages: egg, nymph, and adult. The nymph resembles a small adult and undergoes gradual development through molts. Complete metamorphosis has four stages: egg, larva, pupa, and adult. Three-stage development is characteristic of insects like grasshoppers and true bugs.

Metamorphosis is the biological process where a larva transforms into an adult through drastic changes in body structure and physiology. This process is common in insects, amphibians, and other organisms. Fertilization is the fusion of gametes, cloning creates genetic copies, and metamorphosis is the correct term for this transformation.

Both amphibians and insects have larval forms. They also undergo a process called metamorphosis to come out of the larval stage. In addition to that both use DNA, RNA, ATP, the basic metabolic processes are the same. They are  multicellular organisms. they have a bilateral symmetry, they are both eukaryotes. They have  specializations of cells in regard to sensory, reproductive and metabolic systems. 

Insects shed their exoskeleton in order to grow which is known as moulting. Moulting allows the body of insects to expand under protected conditions. An instar is a developmental stage of insects, between each moult until sexual maturity is reached.

• Molting hormone or Ecdysone is produced by the prothoracic glands which regulates metamorphosis.
  
• It's principle function is to stimulate a series of physiological events (collectively known as apolysis) that lead to synthesis of a new exoskeleton.
• During this process, the new exoskeleton forms as a soft, wrinkled layer underneath the hard parts (exocuticle plus epicuticle) of the old exoskeleton.
  

Grasshoppers, cockroaches, and lice undergo incomplete metamorphosis (nymph stage), whereas mosquitoes undergo complete metamorphosis (egg, larva, pupa, adult).

Winged adults lay eggs on the food plant on which their larvae, known as caterpillars, will feed. The caterpillars grow, sometimes very rapidly, and when fully developed pupate in a chrysalis. When metamorphosis is complete, the pupal skin splits, the adult insect climbs out and, after its wings have expanded and dried, it flies off. Some butterflies, especially in the tropics, have several generations in a year, while others have a single generation, and a few in cold locations may take several years to pass through their whole life cycle.

Complete metamorphosis consists of four distinct stages: egg, larva, pupa, and adult.

• The process of growth and metamorphosis in insects is controlled by secretions of prothoracic glands and corpora allata which are ecdysone and juvenile hormone respectively.
  
• Ecdysone stimu­lates growth and shedding of the old cuticle of the larva and the new cuticle is formed beneath the old cuticle.
  
• The juvenile hormone keeps the larval cells active and also controls the qualitative changes in the body during metamorphosis.
  

Metamorphosis is a biological process by which there is a profound change in form from one stage to the next in the life history of an organism, as from the caterpillar to pupa and from the pupa to adult. Some insects, fishes, amphibians, molluscs, crustaceans, cnidarians, echinoderms and tunicates undergo metamorphosis. Humans do not undergo metamorphosis.
So, the correct answer is 'Both B and C'

Neurology is the study of structure and function of neurons.