Growth at the cellular level is the increase in the amount of:

$A$ leaf of $20 \; cm^{2}$ grows $5 \; cm^{2}$ per hour and a leaf of $25 \; cm^{2}$ grows $5 \; cm^{2}$ per hour. The relative growth rate of leaf $A$ and $B$ respectively is:

Nastic movements differ from tropic movements in being

When certain tomato plants are kept in a dark room for a few days,they develop an albinism-like color. What is this phenomenon called?

'Both growth and differentiation in higher plants are open'. Comment.

Plant growth is unique because