Origin and evolution of metazoa, Biology

Assignment Help:

Origin and Evolution of Metazoa

Most of the early metazoans were soft bodied and so their fossils are rare. The extremely fragmented fossil record does not shed any specific light on their origin. Therefore, 'most of the explanations on their origin are based on their embryology and -comparative morphology. A series of theories have been put forward to explain the origin of multicellular metazoans from unicellular organisms. Of these, three principal theories could be considered.

1) Syncytial Theory: That the ancestral metazoans have arisen from a multinucleate. ciliate by compartmentalization or cellularization.

2) Colonial Theory: That the ancestral metazoans have arisen from colonial flagellates by cellular specialisation and interdependency.

3) Polyphyletic Theory: That the metazoans have arisen from more than one group of organisms.


Related Discussions:- Origin and evolution of metazoa

Intermediate filaments - role of cytoskeleton structures, Intermediate fila...

Intermediate filaments - Role of Cytoskeleton Structures These filaments are intermediate in size among microtubules and microfilaments and are 10 nm in diameter. Five classes

Glands and its types, Glands A cell, tissue or organ which secretes ...

Glands A cell, tissue or organ which secretes specific chemical secretion is known as a gland. The glands develop from the epithelium tissues. The glands are classifi

Etiological factor of diverticular disease, Q. Etiological factor of divert...

Q. Etiological factor of diverticular disease? The causes of diverticular disease are not certain, but several factors may contribute to changes in the wall of the colon. These

Abnormal violent contractions of skeletal muscles, Person Z swallowed a lar...

Person Z swallowed a large amount of substance X and, as a result, has convulsions (abnormal violent contractions of skeletal muscles).  Swallowing which of the following substance

How is the ovulation date estimated, How is the ovulation date estimated wi...

How is the ovulation date estimated with the control of the woman's body temperature? One method to estimate the exact ovulation day is daily control of the body temperature ta

Food and diet, 3 main ways in which the body uses food

3 main ways in which the body uses food

Spastic and obstructive constipation, Q. Spastic and Obstructive constipati...

Q. Spastic and Obstructive constipation? Spastic constipation: It results from excessive tone of the colonic muscle. Obstructive constipation: It occurs usually due to obstr

What is biogenetic law and define bilateral symmetry, What is Biogenetic La...

What is Biogenetic Law and define Bilateral symmetry? In brief, ontogeny recapitulates phylogeny. Or, developmental or embryological sequence of an animal repeats the evolution

What will the responses look like expain, You have a neuron with a resting ...

You have a neuron with a resting potential of -55 mV, EK of -70 mV, and ENa of 50 mV. You decide to voltage clamp the neuron. Now, draw the membrane current over time. What will th

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd