Which factor determines the direction of movement of the main root and stem?

The phase of maturation is characterised by:
$I.$ Cells attaining their maximal size
$II.$ Proper wall thickening and protoplasmic modification
$III.$ Rapid cell division
Select the correct option.

Assertion $(S)$: Growth occurs when anabolic processes exceed catabolic processes.
Reason $(R)$: Growth is the result of metabolism.
$(A)$ Both $S$ and $R$ are true,and $R$ is the correct explanation of $S$.
$(B)$ Both $S$ and $R$ are true,but $R$ is not the correct explanation of $S$.
$(C)$ $S$ is true and $R$ is false.
$(D)$ $S$ is false and $R$ is true.

Growth in plant organs is:

Given below are two statements about plant growth.
Statement $I$: Curve for arithmetic growth is linear.
Statement $II$: Curve for geometric growth is exponential.
In the light of the above two statements,choose the most appropriate answer from the options given below.

Clinostat is employed in the study of