G RI???.4 89%0 10:11 PM Announcements environments? 22) What benefit would being
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G RI???.4 89%0 10:11 PM Announcements environments? 22) What benefit would being a hermaphrodite confer on a parasitic specie? 23) What are the defining characteristics of the chordates? Discuss the evolutionary relationships of chordates to other taxa 24) Give some examples of non vertebrate chordates and discuss their characteristics 25) What are the differences between lancelets and tunicates? How do they differ from vertebrates? 26) What are the differences between vertebrates and other chordates? Explain how cartilage and bone contributed to increased size in vertebrates 27) What are the major groups of fishes? What is the lateral line system in fishes? How does it function? 28) What limits the ability of amphibians to occupy the full range of terrestrial habitats and allows other terrestrial vertebrates to occupy them successfully? 29) List some of the advantages that the early birds, in which flight was not nearly as efficient as it is in most of their modern descendants, might have had as a result of the presence of feathers 30) Discuss the characteristics and major groups of reptiles Explain the significance of the evolution of the amniotic egg 31) List the key characteristics of birds. Why do some consider birds to be one type of reptile? What traits do birds share with reptiles? 32) What are the characteristics of mammals? What are the three groups of mammals? Compare and contrast the groups of mammals 33) How similar is the placenta to the egg of a reptile or bird?Explanation / Answer
22] Hermaphrodites are those organisms which have both the male and female sex organs i.e they can produce both male and female gametes. During the reproductive phase, one individual behaves as a male and while the other behaves as a female. This gives the organisms more area for manipulation and a greater chance of reproduction even if the conditions are adverse.
23] The defining charactersistics of Chordates are--
* presence of a notochord at any stage of life
* a dorsal hollow nerve cord
* pharyngeal gill slits
* presence of a post anal tail
Phylum chordata is an extremely diverse phylum . Vertebrates have originated from chordates. This is clear from the fact that almost all the characteristics of chordates are seen in the embryo of higher vertebrates and at some stage in the life cycle of lower vertebrates.
Hemichordates and protochordates further lend strength to this belief. In fact, these provide a link between chordates and non-chordates. They lack a vertebral column but have a notochord at any stage of their life, either larval or adult . Examples are balanoglossus and amphioxus.
24] Non-vertebrate chordates are called protochordates. They have a bilaterally symmetrical, triploblastic and coelomate body.
The notochord, a hollow flexible rod like structure , makes its appearance for the first time. The notocord separates the nervous tissue from the gut and gives support to the body. It provides a place for muscles to attach for ease of movement. They are marine animals.
However, notochord might not be pesent at all stages of the protochordate's life , or for the entire length of the animal .
In balanoglossus, notochord is present in the larval stage but is not seen in the adult [ larva is considered more developed than the adult] .
Herdmania and balanoglossus are other examples of non - vertebrate chordates.
25] Lancelets and tunicates are two groups of chordates.
Tunicates belong to the sub- phylum Urochordata.. They are sessile marine chordates and lack a backbone .
They represent an early stage in chordate evolution.
They showed paedomorphosis , that is, their larvae were sexually mature.
Lancelets belong to the sub-phylum Cephalochordata.
They are also marine and lack a backbone and are small , blade shaped in structure.
The anterior end of their dorsal nerve cord is slightly swollen. They do not have a proper brain.However, researchers have isolated the same 'Hox' genes that organises the major regions of the brain in vertebrates, in small clusters of cells in the lancelet nerve cord. This has led to the belief that the vertebrate brain might have evolved from the tiny swollen tip of the lancelet's nerve cord.
They differ from vertebrates in that they do not have a backbone or a cranium. They do not have a brain.
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