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?

(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.

Option A is not possible because a 75 kDa protein is too large to diffuse through the plasma membrane.

Option B also cannot be assumed without more information. Even though the addition of QGF does not affect the cell division or survival of glial cells, there may be other signaling pathways that are triggered.

Option D is also not possible because the same receptor would give rise to the same signaling cascade.

Option C is correct - QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.

Assuming it was the same cascading pathway, the same responses would be observed. However, this is not the case (heart muscle cells - cell contraction; fibroblasts - cell division; nerve cells - death; glial cells - no effect). Therefore, the different responses are due to different pathways.

Final answer:

Given the diverse effects of QGF on different cell types, the correct statement is that QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells, due to the specificity of cell surface receptors and the signaling cascades they initiate.

Explanation:

The observation that a previously unidentified extracellular signal molecule, QGF, has different effects on various cell types (increasing contraction in heart muscle cells, inducing division in fibroblasts, causing death in nerve cells, and having no effect on glial cells), suggests specificity in the way cells respond to QGF. The most accurate statement considering these observations is that QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. This specificity is likely because cells have protein receptors on their plasma membranes that, upon binding to a signal molecule like QGF, initiate a cascade of intracellular signals that result in diverse cellular responses. This complexity underscores the concept that the same extracellular signal can lead to vastly different outcomes depending on the cell type, due to the presence of specific receptors and the unique signaling pathways activated within each cell type.

Option (c), "QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed" is the correct option. This option best explains the varied effects of QGF based on established principles of cell signaling involving receptor-ligand interactions and the activation of specific intracellular pathways. Such specificity in response mechanisms highlights the role of cell surface receptors and the tailored intracellular signaling cascades that they initiate, which can lead to a range of cellular outcomes including division, death, or functional modulation.

what is operant behaviour​

When mosquitoes are abundant, purple martins flock to the area and feed exclusively on them. When mosquito populations are not large, purple martins are similarly scarce and feed on other insects. This is an example of A) density-independent regulation. B) density-dependent regulation. C) ecosystem carrying capacity. D) community carrying capacity.