What is the middle lamella composed of?

Each of the following terms has some anatomical significance. What do these terms mean? Explain with the help of line diagrams.
$(A)$ Plasmodesmata
$(B)$ Middle lamella
$(C)$ Secondary wall

Which one of the following is present outside the plasma membrane but inside the cell wall?

How many micelles combine to form a microfibril?

$P -$ Statement: The middle lamella is composed of cellulose plates.
$Q -$ Statement: During the formation of gametes,cell division occurs by mitosis.

What is the remaining part of a cell called after the cell wall is removed?