Many cells function properly and divide mitotically even though they do not have

The number of chloroplasts in a mesophyll cell is:

In the given figure,what do $a$ and $b$ represent respectively?

What are $P$ and $Q$ in the given organelle?

The thylakoids in chloroplasts are arranged as

$A$: Chromoplasts are coloured plastids found in the corolla and ripened fruits.
$R$: They contain water-soluble chlorophyll and carotenoid pigments.