In active transport,

Match the following columns regarding membrane transport mechanisms:

Column-$I$	Column-$II$
$P$. Uniport	$I$. $A$ molecule moves across the membrane independent of other molecules.
$Q$. Symport	$II$. Two molecules move in opposite directions.
$R$. Antiport	$III$. Two molecules cross the membrane in the same direction.

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.

Match the following columns:

Column-$I$	Column-$II$
$P$. Diffusion	$I$. Along the gradient, with protein
$Q$. Facilitated transport	$II$. Against the gradient
$R$. Active transport	$III$. Along the gradient, without protein

Read carefully the given table and choose the option that correctly fills the blanks in it.

Property	Simple Diffusion	Facilitated Transport	Active Transport
Requires special membrane proteins	No	$a$	Yes
Transport saturates	No	Yes	$b$
Uphill transport	$c$	No	Yes
Requires $ATP$ energy	No	No	$d$

Identify the values for $a, b, c, d$.

Diffusion occurring along the concentration gradient and mediated by carrier molecules is known as: