13. ANSWER : OPTION 2. The temperature receptors located in the skin detects the changes in the temperature and they send signals to the temperature regulator center which is located in the hypothalamus which further gives a to regulate the temperature. 14. ANSWER : OPTION B When G protein is activated,aplha subunit detaches by binding with GTP.Now, both aplha GTP unit and beta-gamma dimer,activate second messenger pathways.ie. they activte adenyl cyclase which is an enzyme present in the cell membrane. Activated G protien does not open calcium channels.so option A,C are wrong. Activated adenyl cyclase further convert cytoplasmic ATP into cyclicAMP OR cAMP.Hence,activation of G protein increases the level of cAMP.So, option D is wrong. 15. ANSWER : OPTION A G protien act as a link between the first messenger (the hormone) and the second messenger(cAMP).Hormone comes and binds to the G protein complex which is located in the cell membrane,and it produces cAMP by activating adenyl cyclase.