Transport occurs along the concentration gradient.

Select the incorrect statement with respect to facilitated diffusion.

In a $X$, both molecules cross the membrane in the same direction; in an $Y$, they move in opposite directions.

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

Read carefully the following statements and choose the right answer from the options given below.
$I$. Diffusion is a slow process and it does not depend upon the living system.
$II$. Usually,the process of diffusion does not need energy.
$III$. Diffusion can occur from one part of a cell to another part of the same cell,or from one cell to another,and from one tissue to another tissue.
$IV$. Diffusion is a rapid process over short distances,but extremely slow over long distances.

In mass flow,various substances move independently according to their