The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true? And why? (5points)(a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells.(b) Glial cells do not have a receptor for QGF.(c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.(d) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.

Part (A)  

It isn't Possible. A seventy five kDa super molecule is just too giant to diffuse through the cell membrane.

Part (B)  

It cannot be assumed without information. Although, the addition of QGF doesn't have an effect on the cellular division or survival of glial cells, there is also different signaling pathways that are triggered.

Part (C)  

QGF activates completely different intra-cellular sign pathways in cardiac muscle cells, fibro-blasts, and nerve cells to provide the various responses ascertained.

If it had been identical cascading pathway, you'd get identical responses. However, this is often not the case (heart muscle cells - cell contraction; fibro-blasts - cell division; nerve cells - death; interstitial tissue cells - no effect). Therefore, the various responses are because of different pathways.

Part (D)  

It is additionally impossible. Identical receptor would end in the same communication cascade.

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the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.