Outside of the U.S., many cruise lines do not have automatic tipping policies, says McDaniel, as other countriesâ tipping customs are different than ours (and thus their staff is paid differently), so it may pay to look at cruises leaving from other countries and then look at their âsuggestedâ tipping options.
Best Answer: Active transport is the mediated process of moving particles across a biological membrane against a concentration gradient. If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient.
Active Transport. Only a small number of materials can pass through the plasma membrane by passive diffusion -- if it were open to everything, it wouldn't be a barrier. Yet cells need to control the movement of a variety of other molecules in and out of their membranes to maintain homeostasis.To do this, cells have devised a variety of transport systems. These are proteins embedded in the lipid bilayer that act as gates, which the cell can open and close.et cells need to control the movement of a variety of other molecules in and out of their membranes to maintain homeostasis. To do this, cells have devised a variety of transport systems. These are proteins embedded in the lipid bilayer that act as gates, which the cell can open and close.