-Second messengers are molecules that relay signals received at receptors on the cell surface; such as the arrival of protein hormones, growth factors, etc., to target molecules in the cytosol and/or nucleus.
-Many of the chemical messengers such as hormones, that transmit messages from one cell to another never enter the target cell, these molecules are known as first messengers which work by binding to a specific receptor on the cell surface. The receptor then stimulates or inhibits the production of a so-called second messenger within the cell.
-The second messenger are small molecules such as Cyclic AMP, which activate an effector within a cell.
Warm because land gains heat faster than water when heated by the sun. The heated land then transfers the heat to the atmosphere. The air mass is dry becasue a continent is mainly land and very little water (unlike oceans). There is, therefore, very little moisture in the continental tropical air mass.
It is the basic unit of energy for all functions of the cell without ATP the ions wouldn't be able to transport across the cell membrane. I hope this helps!
