15. Which of the following are considered sources of "Chemical Pollutants?"
A. man made fertilizers
B. insecticides
C. pesticides
D. All the above

its probably

D. all the above

Explanation:

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The sequence of answer is: 3. > 1. > 5. > 2. > 4.

Explanation:

Signal Transduction is the process by which impulses or information about the external environment are transferred from the exterior of the cell to the interior of the cell so that the cell can give the appropriate response.The sequence of signal transduction involves the following steps:The signal molecule that carries the information of the external environment of the cell binds to its cognate receptor molecule, usually present on cell surface, or inside the cell.This binding causes a change in the conformation of the signal-receptor complex molecule which in turn activates an enzyme, associated with the receptor molecule.This  causes the release of secondary messenger molecules like calcium ions, etc, from the endoplasmic reticulum or mitochondria or formation of cyclic AMP (adenosine monophosphate).They causes the activation of protein kinase by binding to them.The activated protein kinase phosphorylates target proteins that may give different responses like transmission of the signal to the nucleus for the transcription of genes or can bring about alternation of cell structure by causing change in the cytoskeletal arrangement in the cells.