In active transport,

$A-$ In an antiport,both molecules move in opposite directions.
$R -$ In symport,only one molecule crosses the membrane in the same direction.

The $Na^+/K^+$ pump is an example of ..........

By what mechanism does water move through the vessels and tracheids of roots, stems, and leaves?

Read the following statements regarding porins and select the correct option given below:
$I$. Porins are transport proteins.
$II$. Channel proteins are a type of transport protein,which are usually gated.
$III$. Carrier protein binds the particular solute to be transported.
$IV$. Particular solute is delivered to the other side of the membrane by carrier proteins.

In the light of the carrier concept,the transport of ions across the membrane is: